Because Mom Said So: The Infection Myths We Grew Up With

Summary

Don’t go outside with wet hair. Put on a coat or you’ll catch a cold. Green mucus means you need antibiotics. Once the fever breaks, you’re not contagious anymore. And whatever you do, don’t sit on that toilet seat.

Generations of parents have passed down rules about how we get sick—but were they actually wrong? In this episode, we revisit the infection myths many of us grew up with and follow the science behind them, from cold weather and respiratory viruses to fever, mucus, toilet seats, lice, and the five-second rule. Along the way, we discover that Mom often noticed something real. She just didn’t always have the mechanism quite right.

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Full Episode

“You’re Going to Catch Your Death”

I don't know about you, but my mom always said things like: Don’t go outside with wet hair. You’ll catch a cold. And for the love of God, put some shoes on. Don’t sit on that toilet seat. Don’t swim yet—you just ate. Green snot? You need antibiotics. If one kid in the class has lice, disinfect everything. Sheets, towels, stuffed animals, coats. Possibly the child. And once the fever breaks, you’re fine. Back to school.

If you grew up with parents—or grandparents, teachers, coaches, camp counselors, or really any adult who felt personally responsible for keeping you alive—you probably heard some version of these. And depending on where and when you grew up, there were probably a few extras. Don’t sleep with the window open. Don’t go outside barefoot. Don’t sit too close to the air conditioner. And, of course, the wonderfully ominous: “You’re going to catch your death.” Which, as childhood public-health messaging goes, is certainly memorable.

But here’s the thing. Most of these rules came from people noticing real things.

As I've mentioned before, humans are very good at spotting patterns. We are slightly less reliable at figuring out what they mean. Add a few generations of parental anxiety, and suddenly wet hair causes pneumonia, green mucus requires antibiotics, and somewhere there is a bacterium patiently staring at a French fry on the floor and counting to five.

So today, we’re doing some parent myth busting. Which of the things we were told growing up are completely wrong? Which contain a surprising kernel of truth? And which ones actually matter?

This is Because Mom Said So: The Infection Myths We Grew Up With

And we’re starting with perhaps the most enduring parental warning of them all. Put on a coat. Because apparently… you’ll catch a cold. And did I mention I feel compelled to say this to my son for no reason other than it was drilled into me and it feels like I must say it. Fighting the indoctrination can be hard.

Can Being Cold Give You a Cold?

So, let’s begin with the easy answer. No. Going outside without a coat does not magically generate a rhinovirus in your respiratory tract. Neither does having wet hair, walking around barefoot, or sitting next to a drafty window. To get a viral respiratory infection, you have to encounter the virus.

So if you walk outside on a freezing January morning immediately after washing your hair, you may feel cold and be uncomfortable. Your hair may actually freeze, which is its own unpleasant experience. But the cold air cannot create a cold virus that wasn’t there before. And yet… this is exactly the kind of myth where saying “FALSE!” and moving on misses the interesting part.

Because the truth hiding in here is that we do get more respiratory infections when it’s cold. There really is seasonality to many respiratory infections. So if cold weather doesn’t cause colds, why do colds seem to arrive with cold weather?

Well, there isn’t one single answer. First, cold weather changes what we do. When it’s cold outside, we tend to spend more time indoors with the windows closed. Unless you're like me and open those babies up to let the cold air in. But nevermind me. In general, people gather in enclosed spaces in cold weather. Kids spend hours together in classrooms. Holiday gatherings bring multiple households together. And if someone in that room is shedding a respiratory virus, being indoors together with poor ventilation can make transmission easier.

But the environment itself changes too. Temperature and humidity can affect respiratory viruses and the particles that carry them through the air. Different viruses respond differently, but cooler, drier conditions can favor the transmission of some respiratory viruses in ways that have nothing to do with whether you remembered your scarf.

And we also have to consider that cold air may affect us. Your nose isn’t just a convenient opening through which viruses enter your body. The tissues lining your nasal passages are part of your immune defenses. They’re constantly encountering particles, microbes, and viruses and responding to them. Experimental studies suggest that cooler temperatures in the upper airway can weaken some local antiviral defenses, although exactly how much that contributes to everyday cold transmission in people is still being worked out. My point is cooler air can affect those defenses.

So does being cold give you a cold? No. You still need the virus. But could colder conditions help create circumstances in which respiratory viruses transmit more effectively and potentially make the tissues they first encounter a little less effective at defending against them? Yes.

So we can see why the myth developed. Every winter, the temperature drops. People get cold. People get sick. Children run outside without coats and, at some point during a season when respiratory viruses are circulating everywhere, some of those children come home sniffling. You don’t need to be irrational to connect those dots. You just need to be missing a few dots in between.

And that brings us to the more dramatic version of the warning: “Put on a coat or you’ll catch pneumonia.” Pneumonia is not something produced by insufficient outerwear. Although pneumonia can occasionally be noninfectious, most of the time it refers to infection and inflammation in the lungs, and it can be caused by a range of pathogens, including viruses, bacteria, and fungi. Cold exposure itself is not a pneumonia pathogen. There isn’t a temperature at which your lungs simply decide, “Well, she forgot her coat. Time for pneumococcus.”

But once again, the association isn’t completely detached from reality. Some respiratory infections that can lead to pneumonia circulate more during colder parts of the year. The same seasonal factors that affect respiratory-virus transmission can therefore affect when we see illnesses that sometimes progress to pneumonia. The mistake is confusing the conditions associated with transmission with the cause of the infection.

And that distinction is going to come up again and again in this episode. Because a lot of infection myths work exactly this way. We notice that two things happen together, then build a causal story around the pattern. Sometimes that story is close. Sometimes it’s wildly wrong. And sometimes there’s enough truth buried inside it to keep the myth alive for generations.

So here’s our verdict on the first one: No, going outside with wet hair will not give you a cold or pneumonia. You still need exposure to a respiratory virus. But that doesn’t mean cold exposure itself is harmless. If your body loses heat faster than it can produce it, prolonged or extreme cold exposure can lead to cold-related injuries like frostbite and hypothermia—which can become life-threatening. That’s a completely different process from catching an infection: cold can injure you, but it cannot supply the pathogen.

Which means Mom gets partial credit. She can keep the coat. We’re taking away her authority over the wet hair. And while we’re overturning generations of parental diagnostic medicine, we should probably deal with another belief that just persists like the smell of burnt dog poop. Because if that runny nose eventually turns green… someone is going to just know you need antibiotics.

Does Green Snot Mean You Need Antibiotics?

There is a point in almost every respiratory infection when someone looks at a tissue and thinks: Well. That can’t be good. Credit where it's due...one of my first memories of a book that made me stop and think ...ewww...and also...he's not wrong...was in The Shining by Stephen King when one of the characters blew his nose then looked in the tissue to see if got anything interesting. 40 years since I read that book and that I remember. I looked it up to see if I was remembering correctly and sure enough that was in the book. I'm dying.

"He pulled a red-and-blue bandana from his back pocket, blew his nose with a decisive honk, and thrust it back out of sight after a short peek into it to see if he had gotten anything interesting." Watson, The Shining, by Stephen King.

OK, where were we? Oh yes, green snot. So, maybe your nose started running two days ago, and everything was relatively clear and watery. Then it got thicker. Then yellow. And now you've produced something sufficiently green that it seems less like a symptom and more like evidence. Surely that means something bacterial has moved in.

This is one of those beliefs that feels almost self-evident. Clear mucus? Probably allergies or the beginning of a cold. Yellow mucus? Something is brewing. Green mucus? Infection. Antibiotics. We have collectively been carrying around an unofficial mucus color chart for generations.

Except mucus color tells us much less than we think it does. Green or yellow mucus can occur during an infection, and if you’re several days into a cold, infection is an obvious explanation. But the color itself isn’t proof that an infection is present. What it mostly tells us is that the mucus contains the products of inflammation—including large numbers of immune cells. That can happen during an infection, but inflammation can have noninfectious causes too.

And even when an infection is causing the green mucus, color cannot reliably tell us what kind of infection it is. A viral respiratory infection can produce green mucus. So can a bacterial infection. Which means looking at the color cannot tell you whether antibiotics will help. To understand why, we need to talk briefly about what all that stuff actually is. Mucus is there when you’re healthy, too. The lining of your respiratory tract produces it continuously, and it performs some very useful housekeeping. It helps trap particles and microbes before they can travel farther into the respiratory tract, and tiny hair-like structures called cilia help move that material along so it can be cleared.

Then you get a respiratory infection, and things become considerably messier. Inflammation increases. Mucus production changes. Immune cells arrive at the scene. Cellular debris accumulates. And among the immune cells rushing in are neutrophils—some of the body’s rapid-response cells when something potentially dangerous shows up.

Now, mucus color reflects several components such as concentrated inflammatory cells/debris...but those neutrophils also contain an enzyme called myeloperoxidase, which has a greenish color. As large numbers of these immune cells collect in mucus and break down during infection or other inflammatory conditions, they can help turn it yellow or green. In other words, depending on context the color can be evidence that your immune system is responding to an infection. What it cannot reliably tell you is what caused that infection

And this is where a relatively harmless bit of family medical folklore bumps into a much larger public-health problem. Using antibiotics when we don’t need them exposes people to potential side effects without treating the illness that is making them sick, and at the same time, unnecessary antibiotic use contributes to antimicrobial resistance.

Turns out the course of the illness tells us more that mucus color, so pay attention to how your illness progresses so you can tell your doctor. For example, how long have the symptoms lasted? Are they severe? Did you start getting better and then suddenly get worse again? A pattern sometimes called “double worsening”—where symptoms improve and then return or intensify—can raise suspicion for a bacterial sinus infection. it's also important to note if you experience persistent symptoms without improvement or severe symptoms. Doctors need the entire clinical picture to guess right. Obviously testing is too much to ask.

Just kidding. But I know you're thinking it. Why not just swab the mucus and see if bacteria are there? The problem is that bacteria normally live in our noses, so finding them doesn’t prove they’re causing the illness—and getting a reliable sample from inside an infected sinus is considerably more complicated. That’s why clinicians usually rely on the pattern and duration of symptoms rather than the color—or a routine nasal swab—to decide whether antibiotics are appropriate.

So while seeing a glob of green snot pulsing just inside your kids' nostril is disgusting... Green is just a color

So the verdict on green snot is pretty straightforward: No, green mucus does not automatically mean you have a bacterial infection. And no, it does not automatically mean you need antibiotics. It means your mucus is green, which, during a respiratory infection, is not unusual.

So parents, here's my two cents..keep the color chart but use it in context. Note the color but more importantly note the progression of illness so if they get worse or you're concerned yoou can give the doc all the deets. And if the only thing you notice is green snot? Don’t panic. It could be part of a mild infection, or it could have a noninfectious cause. The color alone generally isn’t a reason to head to the doctor or a reason for antibiotics. What matters much more is what else is going on and what happens next.

And let’s give a round of applause to mucus for reminding parents, for generations, that there is a vast difference between your kid’s snot and somebody else’s kid’s snot.

OK, our next parental diagnostic instrument is even simpler.

A thermometer.

Fever: Friend, Foe, or Number on the Thermometer?

There's just something about a thermometer.

A kid can be coughing, congested, tired, cranky, and clearly miserable, but whatever theyre fine...then you take their temperature and see 102.4 and now you have a number and they're legit sick. Numbers feel authoritative. It’s like the thermometer is giving us a severity score: 100.4? Keep an eye on them. 102? Okay, we’re worried. 104? Everybody panic.

And to be fair, parents have been trained to pay attention to those. Pediatricians give us temperature cutoffs and tell us when a fever warrants a call or a closer look. And in certain situations—especially in very young babies—the number really does matter.

The mistake is taking that useful information and turning the thermometer into a universal severity meter: the higher the number, the sicker the kid. That’s not how fever works. And once we start treating temperature like a severity score, a whole bunch of other rules seem to follow: the higher the fever, the worse the infection. You have to get the fever down. And once the fever breaks, the illness is basically over.

Unfortunately, pathogens have not agreed to organize themselves around the thermometer.

So let’s start with what a fever actually is. Your body normally regulates its temperature within a relatively narrow range. During an infection, signals from the immune system can cause the brain’s temperature-regulating center in the hypothalamus to raise that target. Your body then starts behaving as though its current temperature is too low.

That’s why you can have chills while your temperature is actually rising. You feel cold. Blood vessels near the skin constrict. You may shiver. You pile on blankets even though the thermometer says you’re getting hotter. Your body is generating and conserving heat because, from the perspective of the thermostat in your brain, it hasn’t reached the new set point yet.

So, fever isn’t your body overheating. It is a regulated physiological response. And that is very different from hyperthermia, which is what the dangerous overheating of your body is called. And that can occur when the body accumulates more heat than it can get rid of, as in heat stroke. In hyperthermia, the thermostat hasn’t deliberately been turned up. The body’s temperature-control system is being overwhelmed. We use the word “hot” for both situations, but biologically they're very different.

So why would the body deliberately make itself hotter during an infection? Because fever is part of the immune response. Fever-range temperatures can influence pathogen replication and immune function. It is one of the things the body can do when it detects a threat.

That doesn’t mean fever is always harmless, or that a high temperature should be ignored. Age, underlying medical conditions, associated symptoms, how long the fever has lasted, and the overall clinical picture are important. Fever in a very young infant, for example, is treated differently from the same temperature in an otherwise healthy older child or adult.

Some relatively routine viral infections can produce impressive fevers. Serious infections do not always produce very high fevers. Some people with serious infections may have little or no fever at all. So while temperature is useful information, the height of a fever by itself does not neatly tell you how dangerous an infection is.

And parents, if you’re thinking, “Okay, but what about febrile seizures?”—fair question. They’re real, they can be absolutely terrifying to watch, and they occur in some young children during a fever. But they’re not just the result of a fever reaching some universally dangerous number, and fever-reducing medicine has not been shown to reliably prevent them. Most simple febrile seizures are brief and do not cause lasting harm—although a child having a seizure should, of course, be evaluated appropriately.

Then there’s the idea that every fever must immediately be brought back to normal.

Again, fever is part of the immune response, not a malfunctioning thermostat that necessarily needs to be corrected just because the number has moved above 98.6. 98.6 degrees Fahrenheit is not some magical temperature every healthy human maintains at all times. Normal body temperature varies among people and throughout the day.

So don’t panic about getting a fever down. But do ask your pediatrician what temperatures, symptoms, or circumstances should prompt a call for your specific child—and when you’re not sure, call. That’s what they’re there for.

And don’t feel bad about giving your child a fever reducer when they need it to feel more comfortable. If they’re miserable and achy, can’t rest, or aren’t drinking enough, helping them feel better can help them rest and stay hydrated. So follow your pediatrician’s guidance, help your kid feel better, and keep the fluids going. No judgment.

Now let's move on to an infectious-disease-relevant fever myth that happens at the other end of the illness: “The fever broke, so they aren’t contagious anymore.”

There are two different biological processes happening in that sentence so let's clarify this. A fever tells you something about your body’s response. Contagiousness is about whether a pathogen is being shed in a way that allows it to reach another person. Those things can overlap, but there's no universal biological switch connecting them.

Depending on the infection, someone may be contagious before they ever develop a fever. They may remain contagious after the fever disappears. They may transmit the pathogen without ever having a fever at all.

Influenza is a familiar example: people can begin spreading flu virus before they recognize that they’re sick. With other respiratory viruses, presymptomatic or asymptomatic transmission can also occur. And different pathogens have completely different patterns of shedding and infectiousness.

So “the fever is gone” and “I am no longer capable of transmitting this infection” are not interchangeable statements. And this is important for deciding when someone should return to school, work, daycare, or other shared spaces. A thermometer can be useful, and recommendations for particular infections may include being fever-free for a certain amount of time. But those recommendations aren’t based on a universal law that says pathogens disappear when body temperature returns to normal. They’re practical rules built around what we know about particular infections, symptoms, transmission, and recovery.

So, a fever can tell us something important. It just can’t tell us everything.

Next, we’re going to tackle an entirely different category of parental warning.

The Things Kids Touch

Don’t touch that. Don’t put your hands there. Don’t eat that off the floor. And whatever you do, do not sit on the public toilet seat. Childhood, viewed through the eyes of a parent, is essentially one long exercise in watching another human being enthusiastically interact with surfaces you would prefer they never know existed. Have I mentioned my son licked a trash can rim out on the city street? Good news is he was a toddler...not like a teenager...silver linings and all.

Children touch everything, then their faces and lick their fingers or entire hands. They crawl on floors, then eat crackers. They drop food and pick it back up. They put everything they can grab in their mouths. If you spend enough time watching a small child move through the world, germ theory becomes a neverending gauntlet.

But our instincts about which surfaces are dangerous are not always very good, because we tend to confuse “disgusting” with “likely to transmit infection.” Guilty as charged. But those are not the same thing. Instead of wondering is something is dirty or has germs on it, cuz the answer is always yes...we should ask, can a germ that's here actually get from this surface into a part of my body where it can establish an infection?

Which brings us to the public toilet seat, perhaps one of the most feared objects in the parental universe. Generations of children have been warned not to sit on one because they might “catch something,” with the unspecified something often carrying distinctly sexually transmitted undertones. But for most of the infections people imagine acquiring this way, the biology doesn’t cooperate. Intact skin is an excellent barrier. The skin on the backs of your thighs and buttocks is not a particularly convenient portal of entry for pathogens that normally require sexual contact or direct contact with infected mucosal surfaces. And I'm sorry for saying portal of entry in this discussion...ok not really...anyway...sexually transmitted infections are called sexually transmitted infections because they have particular routes of transmission, not because they are lurking on bathroom fixtures waiting for an available backside. For more on this check out last week's Outbreak After Dark.

That does not mean public bathrooms are sterile. Obviously they're not. Toilets, flush handles, faucets, door handles, countertops, and other frequently touched surfaces can become contaminated with microbes. Flushing can also disperse droplets and aerosols containing material from the toilet bowl, which is yet another reason not to confuse “you probably won’t acquire an STI from the seat” with “bathrooms are pristine microbial sanctuaries.” But if we’re thinking about realistic infection risk, your hands are usually much more interesting than your thighs. Touching a contaminated surface and then touching your mouth, nose, or eyes—or handling food before washing your hands—creates a much more biologically plausible pathway for many pathogens. For the common STIs people worry about, toilet-seat transmission is not considered a meaningful route.

And here again, my son reigns supreme.

I’m in a Walmart bathroom. I’m peeing, he’s in the stroller in the stall with me, and he kicks off his shoes and somehow scooches himself down far enough to start rubbing his bare feet all over the bathroom floor.

Cool.

Fine.

Not ideal, but manageable. I’m a virologist. I understand microbes. We’ll sanitize his feet when we get home. Nobody panic.

And then he lifts up one of those Walmart-bathroom-floor feet, grabs it with both of his tiny hands, and puts it directly. Into. His. Mouth.

It happened so fast.

There are moments in parenting when all of your training leaves your body and you’re just standing there thinking, Well. I guess this is who we are now.

So, this is where the parental command “DON’T TOUCH THAT!” becomes both right—and wrong. Yes, contaminated surfaces can matter. For some pathogens, they matter a lot. But transmission depends on the organism, how much of it is present, how long it remains infectious in the environment, what you do after touching the surface, and whether it reaches an appropriate route into the body. Finding a pathogen—or even genetic material from a pathogen—on a surface does not automatically mean touching that surface will make someone sick.

So, did my son get sick? Interestingly, with the trash can rim licking he did not get sick...with the walmart floor foot sucking? He did. 2 days later. Can I prove the transmission chain? No. But I'm pretty confident on that one.

Which, brings us to another cherished piece of household microbiology: the five-second rule. You know the rule. Food falls on the floor, someone immediately picks it up, and as long as fewer than five seconds have elapsed, apparently the microbes have not yet completed the necessary paperwork to climb aboard.

Unfortunately, bacteria don't carry stopwatches. Transfer can happen immediately. Researchers who have actually studied this—and I appreciate that somewhere, someone looked at the five-second rule and said, “We should absolutely get data on this”—have found that the amount transferred depends on things like the type of food, the surface it lands on, moisture, contact time, and the specific microorganisms involved. A wet piece of watermelon and a dry cracker are not the same. Neither are carpet and tile. One second and sixty seconds may not produce identical amounts of transfer, but there is no magical five-second grace period during which microbes politely remain on the floor.

Does that mean eating a cracker that touched your kitchen floor for two seconds will definitely make you sick? Also no. This is where risk gets flattened into another overly simple rule. Microbial transfer is not the same thing as infection. For illness to occur, the right pathogen has to be there, remain viable, transfer in a sufficient amount, enter your body through an appropriate route, and successfully establish an infection. Sometimes that chain is plausible. Sometimes it isn’t.

And then there’s lice, which may be the ultimate example of what happens when parental anxiety meets the idea of environmental contamination. One kid comes home with head lice and suddenly the house is undergoing Velveteen Rabbit-level decontamination. Strip the beds. Wash the towels. Bag the stuffed animals. Clean the couch. Vacuum everything. Every hat, pillow, hairbrush, blanket, and possibly the family dog is now under investigation.

Except head lice really, really want to be on your head. They’re highly adapted to living there, feeding on human blood, and staying close to the warm, humid environment of the scalp. Their eggs—called nits—are literally glued to hair shafts. Adult lice that fall off a person generally don’t survive very long because the environment they need is the one you are carrying around on top of your neck. Your couch is not secretly maintaining an independent lice civilization.

And that’s also why another classic warning—“Don’t share hats or you’ll get lice”—isn’t completely impossible, but it puts the emphasis in the wrong place. Head lice spread primarily through direct head-to-head contact. They crawl. They don’t jump, they don’t fly, and they are not waiting inside the communal dress-up hat for their moment. Transmission through hats, brushes, pillows, or other objects that have recently contacted someone’s hair can happen, but it’s thought to be much less common than one head coming into direct contact with another.

So if your child gets lice, you don’t need to treat the entire house like a biohazard zone or start spraying insecticides all over the furniture. The important biology is happening on the head. Which gives us perhaps the easiest infection-control rule of the entire episode: think heads, not houses.

And that may be the bigger lesson hiding inside all of our anxieties about dirty surfaces. Humans are understandably disgusted by toilets, garbage cans, muddy floors, hats worn by someone with lice, and mysterious sticky substances on playground equipment. Disgust is useful. It has probably prevented an enormous number of questionable things from entering...humans. But disgust is not a pathogen-specific risk assessment.

Something can look revolting and pose very little risk for the infection you’re worried about. See exhibit 1, the trash can. Something else can look completely ordinary and be an excellent vehicle for transmission. A clean-looking hand can carry a gastrointestinal pathogen. A beautifully prepared meal can contain a foodborne pathogen you cannot see, smell, or taste. See exhibit 2: rfkjr's HHS and FDA.

So instead of dividing the world into “clean things” and “germy things,” infectious disease asks a more useful set of questions: What organism are we talking about? Where does it normally live? How does it leave one host? How long can it remain infectious outside that host? And, most importantly, how does it get into the next one?

Because once you understand the route of transmission, you can spend less time hovering over a toilet seat and more time paying attention to the things that actually interrupt that route.

“But Mom Always Said…”

At this point, we have taken away quite a few pieces of traditional parental medical wisdom. But there are still a few classics left. And rather than send each one through a full scientific trial, I think it’s time for a lightning round.

First up: “Take some vitamin C so you don’t catch a cold.” This one is more complicated, because vitamin C really does matter for normal immune function. A severe deficiency causes very real health problems. But for most people who are already getting adequate vitamin C, taking extra vitamin C does not create an invisible force field against rhinoviruses.

Research on regular vitamin C supplementation has generally not shown that it prevents the average person from catching a cold, although there is evidence that regular supplementation may modestly shorten the duration of colds or reduce their severity. There are also some circumstances involving intense physical exertion in which studies have suggested a greater preventive effect. But that's not the same as “take this vitamin C because everyone at work is sick and you won’t catch it.”

So if you like oranges, eat an orange. They’re lovely. Just don’t expect the vitamin C to erect a tiny citrus barricade across your nasal passages.

Though vitamin C does have other interesting biological effects. When I was in grad school, we read studies showing that high doses of vitamin C could blunt some of the acute oxidative and blood-vessel effects of cigarette-smoke exposure. At the time I was working in a very smoky bar, so naturally I started taking vitamin C before every shift. Was I conducting an evidence-based occupational-health intervention or just producing very expensive urine? Probably a little of both.

Those studies weren't imaginary. Vitamin C can affect oxidative stress and vascular function, and smokers tend to have lower vitamin C levels. But showing that an antioxidant changes a short-term biological marker after smoke exposure is very different from showing that taking a supplement prevents the diseases caused by smoking. It doesn't make cigarette smoke safe, just like having enough vitamin C doesn't make you rhinovirus-proof.

Next: “You’ll catch a cold walking around barefoot.”

Nope. Colds are caused by respiratory viruses, and they do not enter through your feet. Although, fun fact: in certain parts of the world, walking barefoot on soil or sand contaminated with the right parasites can allow hookworm larvae to penetrate your skin—so Mom was worried about the wrong pathogen, but apparently not entirely wrong about shoes.

“Stop biting your fingernails or you’ll get worms.”

Okay, Mom. You win this one.

Biting your nails does not magically generate worms, but pinworm eggs can get onto hands and underneath fingernails, and putting contaminated fingers in your mouth is one way those eggs can get into your body. Nail biting has actually been associated with a higher risk of pinworm infection in kids.

So was the biology completely made up? Annoyingly, no.

And finally, one of the oldest pieces of illness advice of all: “Feed a cold, starve a fever.”

Or possibly “starve a cold, feed a fever,” depending on who taught it to you, which is perhaps our first clue that we should not build a clinical nutrition strategy around it.

But this one has an interesting wrinkle. Scientists really have found that feeding and fasting can change metabolism and immune responses during infection, and animal studies suggest those effects may even differ depending on the type of infection. That's fascinating biology but it has not translated into evidence that you should deliberately starve yourself, or your kid, because you have a fever.

Illness often decreases appetite all by itself. You don't need to force-feed someone who doesn't feel like eating, but you also don't need to withhold food from someone who's hungry. Eat as tolerated, pay attention to hydration, and please don't make Grandma's rhyme your metabolic treatment protocol.

And I think that’s enough parental wisdom dismantled for one day.

And to be fair, as we've seen, they weren’t crazy. They were trying to make sense of why people get sick.

Parents Weren’t Crazy. Pathogens Are Just Complicated.

Infectious disease can make the world feel like there's danger everywhere because microbes are everywhere. But microbes being everywhere doesn't mean every encounter with a microbe is equally risky.

When we misunderstand how infections happen, we can spend an enormous amount of effort protecting ourselves from the wrong things. Understanding the mechanism lets us redirect that attention toward the things that actually matter.

Sometimes that means ventilation and cleaner indoor air. Other times it can mean washing your hands, or cleaning and disinfection, or vaccination. Sometimes it means staying home when you’re sick and sometimes it means doing absolutely nothing about the toilet seat.

The goal was always to keep us safe. Science just gives us better information about where to put the coat, when to wash the hands, when antibiotics actually help, and which things we can stop worrying about.

So, Mom, you were right about a lot of things. You were right that winter and respiratory infections are connected. You were right that kids bring a lot of things home from school. You were definitely right that I should wash my hands before eating. And honestly, you were probably right that I should dry my hair before walking outside in January. It’s cold. Wet hair is miserable. My hair might freeze.

You were just wrong about the rhinovirus waiting for me on the porch.

Annotated Citations

Each citation is annotated to explain how the source connects to the episode and to help listeners who want to explore the science in greater depth.

Accessing the literature: Whenever possible, I've linked directly to free full-text articles and books that are legally available online. For subscription-only journal articles, many researchers are happy to share a personal copy of their work if you contact the corresponding author. For books, I've included links to free online lending copies or library catalogs when available. If a title isn't freely available online, I've linked WorldCat to locate it at a nearby library or you can ask your local library about interlibrary loans.

Cold weather, respiratory viruses & seasonality

• Leung NHL. 2021. Transmissibility and transmission of respiratory viruses. Nature Reviews Microbiology.

  → An excellent overview of how respiratory viruses move between people and how environmental conditions, human behavior, and differences among viruses influence transmission. Useful context for why respiratory illness really is seasonal even though being cold does not itself give you a cold.

  🆓 Open access: https://www.nature.com/articles/s41579-021-00535-6

• Neumann G, Kawaoka Y. 2022. Seasonality of influenza and other respiratory viruses. EMBO Molecular Medicine.

  → A mechanistic look at why many respiratory viruses flourish at particular times of year, including the roles of temperature, humidity, viral biology, and host defenses. Especially useful for the episode’s distinction between cold weather causing infection and cold conditions changing the environment in which infection occurs.

  🆓 Open access: https://link.springer.com/article/10.15252/emmm.202115352

Green mucus & antibiotics

• Klebanoff SJ, et al. 2013. Myeloperoxidase: a front-line defender against phagocytosed microorganisms. Journal of Leukocyte Biology.

  → A deep dive into myeloperoxidase, the distinctive green heme-containing enzyme abundant in neutrophils. It explains the biology behind the episode’s green-snot detour: when large numbers of neutrophils accumulate during inflammation, their myeloperoxidase can contribute to the green color we associate with purulent mucus. Importantly, that immune response does not tell us whether the underlying infection is viral or bacterial.

  🆓 Open access: https://pmc.ncbi.nlm.nih.gov/articles/PMC3545676/

• CDC. 2025. Healthy Habits: Antibiotic Do’s and Don’ts.

  → A wonderfully direct source for one of this episode’s central myths: CDC specifically notes that colds and runny noses do not need antibiotics even when mucus becomes thick, yellow, or green. A useful reminder that mucus color alone cannot tell you that an infection is bacterial or that antibiotics will help.

  🌐 Free online resource: https://www.cdc.gov/antibiotic-use/about/

• CDC. 2024. Sinus Infection Basics.

  → What matters more than the color of your mucus? The pattern of illness. CDC notes that most sinus infections are viral and highlights the clues clinicians use when bacterial sinusitis becomes more concerning—including symptoms lasting more than 10 days without improvement, severe symptoms, or getting better and then getting worse again.

  🌐 Free online resource: https://www.cdc.gov/sinus-infection/about/index.html

Fever, fever reducers & febrile seizures

• Sullivan JE, Farrar HC; American Academy of Pediatrics. 2011, reaffirmed with updates 2022. Fever and Antipyretic Use in Children. Pediatrics.

  → An excellent source for separating what fever actually tells us from what parents understandably fear it means. The AAP explains that fever is a physiological response rather than an illness itself, that the height of a fever does not always correspond to illness severity, and that the goal of fever-reducing medication should generally be improving a child’s comfort rather than forcing the thermometer back to “normal.”

  🌐 Free online resource: https://publications.aap.org/pediatrics/article/127/3/e20103852/65016/Fever-and-Antipyretic-Use-in-Children

• Di Giovine M, Catenaccio E. 2025. Febrile Seizures in Children. HealthyChildren.org, American Academy of Pediatrics.

  → A parent-friendly companion to the clinical literature on febrile seizures. These seizures can be frightening to witness, but most are brief and do not cause lasting harm. They can occur even with milder fevers, and acetaminophen or ibuprofen can lower fever but do not prevent febrile seizures.

  🌐 Free online resource: https://www.healthychildren.org/English/health-issues/conditions/fever/pages/Febrile-Seizures.aspx

Surfaces & transmission

• La Rosa G, Fratini M, Della Libera S, Iaconelli M, Muscillo M. 2013. Viral infections acquired indoors through airborne, droplet or contact transmission. Annali dell'Istituto Superiore di Sanità.

  → A useful overview of the different routes viruses can use to move between people indoors. It supports one of the episode’s central ideas: finding microbes on a surface is not enough to tell us how much infection risk that surface poses—the organism and its actual route of transmission matter.

  🆓 Open access: https://www.scielosp.org/article/aiss/2013.v49n2/124-132/en/

The five-second rule

• Dawson P, Han I, Cox M, Black C, Simmons L. 2007. Residence time and food contact time effects on transfer of Salmonella Typhimurium from tile, wood and carpet: testing the five-second rule. Journal of Applied Microbiology.

  → Yes, scientists actually tested the five-second rule. They found that bacterial transfer can occur within seconds and that surface type and other conditions affect how much is transferred. In other words: microbes do not wait politely for the countdown to finish.

  🔒 Subscription required: https://academic.oup.com/jambio/article-abstract/102/4/945/6718586

Head lice

• CDC. 2024. About Head Lice.

  → Current public-health guidance behind our rule to “think heads, not houses.” Head lice spread mainly through direct head-to-head contact; spread through hats, brushes, bedding, furniture, and other objects is possible but less common. Lice generally die within about two days after falling off a person, and CDC specifically says spending large amounts of time and money cleaning the house is unnecessary. 🌐 Free online resource: https://www.cdc.gov/lice/about/head-lice.html

• CDC. 2024. Treatment of Head Lice.

  → Practical guidance for what actually does need attention after a case of head lice. CDC recommends dealing with recently used clothing, bedding, combs, and brushes and vacuuming areas where the person sat or lay—but emphasizes that the risk from lice that have fallen onto furniture or carpet is very small. And no fumigating: sprays and fogs are unnecessary and can be toxic.

🌐 Free online resource: https://www.cdc.gov/lice/treatment/index.html

Vitamin C & the common cold

• Hemilä H & Chalker E, 2013. Vitamin C for preventing and treating the common cold. PLoS Medicine.

  → A systematic review behind the much less exciting reality of vitamin C and colds: routine supplementation doesn't prevent colds in the general population, although it may modestly reduce their duration or severity, with stronger preventive effects reported under some conditions of intense physical stress.

  🆓 Open access: https://pmc.ncbi.nlm.nih.gov/articles/PMC8078152/

Vitamin C, cigarette smoke & vascular effects

• Münzel T, et al. 2020. Effects of tobacco cigarettes, e-cigarettes, and waterpipe smoking on endothelial function and clinical outcomes. European Heart Journal.

  → Modern context for the vitamin-C-and-smoking studies mentioned in the episode. Cigarette smoke produces oxidative stress and vascular dysfunction, and antioxidant experiments—including vitamin C studies—have demonstrated effects on short-term biological measures. That's interesting mechanistic evidence, but it does not mean taking vitamin C protects someone from the health consequences of smoking.

  🆓 Open access: https://academic.oup.com/eurheartj/article/41/41/4057/5861975

Bare feet & skin-penetrating parasites

• McClure CR, Patel R, Hallem EA. 2024. Invade or die: behaviours and biochemical mechanisms that drive skin penetration in Strongyloides and other skin-penetrating nematodes. Philos Trans R Soc Lond B Biol Sci.

  → For the episode's wonderfully unfortunate exception to “you won't catch anything through your feet.” Some parasitic nematode larvae really can penetrate human skin after contact with contaminated soil. Respiratory viruses still aren't entering through your feet—but Mom's insistence on shoes wasn't completely useless.

  🆓 Open access: https://pmc.ncbi.nlm.nih.gov/articles/PMC10676818/

Nail biting & pinworms

• Wendt S, et al. 2019. The diagnosis and treatment of pinworm infection. Deutsches Ärzteblatt International.

  → The irritating moment when Mom turns out to have a point. Pinworm eggs can contaminate hands and collect beneath fingernails, allowing them to reach the mouth, and nail biting is recognized as a risk factor for infection.

  🆓 Open access: https://pmc.ncbi.nlm.nih.gov/articles/PMC6522669/

“Feed a cold, starve a fever”

• Sankararaman S, Venegas C, Seth S, et al. 2024. “Feed a Cold, Starve a Fever?” A review of nutritional strategies in the setting of bacterial versus viral infections. Current Nutrition Reports.

  → Grandma's rhyme turns out to contain a much more interesting scientific question than it first appears. Research suggests that nutrition, fasting, metabolism, and immune responses can interact differently during different infections—but that fascinating biology does not amount to clinical evidence that people with fever should deliberately starve themselves.

  🔒 Subscription required: https://link.springer.com/article/10.1007/s13668-024-00536-w

Cultural Reference

• King S. 1977. The Shining. Doubleday.

  → The source of Watson’s—apparently unforgettable—inspection of his handkerchief after blowing his nose, referenced in the episode during our discussion of green mucus. No infectious-disease evidence here. Just Stephen King making sure I would remember this particular detail for the next forty years. I enthusiastically recommend this book.

  📚 WorldCat (find at a library near you):  https://search.worldcat.org/title/1179298969