*Only a virus — never wet hair or cold air alone — can cause the common cold. But recent research shows cold temperatures genuinely weaken your nose's defenses.*

Picture the scene: you are twelve years old, your hair still dripping from the shower, one hand on the front door, and a voice rings out from the kitchen — your mother, your grandmother, some guardian of domestic wisdom — warning you that if you step outside like that you will catch your death. Or at least a cold. You probably rolled your eyes, went out anyway, and if you did get sick a few days later, the household verdict was already written: she told you so.

This scolding is one of the most durable pieces of health folklore on the planet. It crosses cultures and generations. In some households the warning is about wet hair; in others it is about dressing too lightly for cold weather, sitting in a draft, or sleeping with the window open. The underlying belief is always the same: being cold, damp, or chilled can give you a cold.

Doctors have spent decades telling the public this is not how colds work. And on the strict question — can wet hair or chilly air give you a cold? — the medical establishment is unambiguous. But over the past two decades, a series of experiments, some of them ingenious, has revealed something more complicated: your grandmother was wrong about the mechanism, yet not entirely wrong that cold and colds are connected. This is a myth with a kernel of truth, which is exactly why it has survived every attempt to kill it.

The claim everyone grew up hearing

The belief that cold and dampness cause respiratory illness predates the entire field of microbiology. Before germ theory took hold in the late nineteenth century, the dominant explanation for disease was miasma — “bad air.” Physicians and ordinary people alike believed that foul vapors, cold drafts, and damp conditions could generate sickness in the body directly. Being chilled, in this worldview, was not a risk factor for illness; it was a cause of it.

When scientists discovered that microorganisms cause disease, the old warnings did not retire. They simply attached themselves to the new vocabulary. The common cold was named after its most visible correlate — it strikes hardest in the cold months — and the name itself reinforced the idea. Generations of parents passed the warning down with the confidence of firsthand evidence: every winter, the children went out underdressed, and every winter, the children got sick. Correlation did the rest.

Modern variants of the warning are everywhere. “Don’t go outside with wet hair, you’ll catch a cold.” “Bundle up or you’ll get sick.” “That draft will give you a sore throat.” Surveys consistently show that a large share of the public still believes, at least half-heartedly, that being cold can cause the common cold. The question is whether any of it survives contact with evidence.

What the doctors say: it is the virus, not the weather

The Mayo Clinic addressed this exact question in a 2022 Q&A, and its answer was blunt. Asked whether going outside with wet hair causes the common cold, the clinic responded: “The short answer is no.” Colds are caused by viruses, the clinic explained, “so you can’t catch a cold from going outside with wet hair. And wet hair won’t make you more attractive to germs.”

The same answer covered dressing for the weather. While warmer clothes are sensible in the cold, the clinic noted that research indicates cold weather — just like going outside with wet hair — does not make you sick.

Infectious disease specialists say the same thing in plainer language. “Going outside with wet hair may make you feel cold, but it doesn’t cause colds. Colds are caused by viruses,” says Dr. William Schaffner, a professor of infectious diseases at Vanderbilt University School of Medicine. To develop a cold or the flu, you have to pick up the virus that causes it, usually through respiratory droplets or contaminated surfaces. Your wet hair does not create a virus where there is not one.

Physicians at the University of Utah’s health system put it in grandmother-defying terms: the wet-hair warning is “a great thing for grandmothers and mothers to tell their children, but there is really no evidence that going out in the cold will get you a cold. We call it a cold, but that’s just the name of it. Colds are caused by viruses, and actually viruses don’t necessarily propagate any better in the cold than they do in warm weather.”

That last point deserves emphasis, because it undercuts a tempting compromise: maybe the cold air itself helps the virus. According to the Utah physicians, the evidence does not support that either. If no virus reaches your nose, no amount of damp hair or icy wind can conjure a cold out of nothing. A virus is a necessary ingredient, and the weather cannot supply it.

So why do colds explode every winter if cold is not the cause? The doctors point to a set of entirely virus-friendly explanations that have nothing to do with your hair. In winter, people spend far more time indoors, packed together in homes, classrooms, and offices — ideal conditions for respiratory droplets to find new hosts. Heating systems and naturally dry winter air dry out the nasal passages, thinning the mucus layer that traps incoming viruses. And as Dr. Anthony Fauci, the former director of the National Institute of Allergy and Infectious Diseases, has explained, “Viruses survive and transmit better in lower humidity, which is common in winter.” Droplets from coughing and sneezing can spread further and hang in drier air longer, as Mayo Clinic virologist Dr. Matthew Binnicker has noted.

In other words, winter is cold season because winter is virus season — crowded, dry, and perfectly arranged for transmission. The cold air is a bystander. Or so the standard account goes.

The experiments that seemed to close the case

The idea that cold exposure cannot cause colds is not just expert opinion; it was tested directly, and for decades the tests agreed. One of the most cited experiments appeared in 1968. Researchers dripped the newly isolated cold virus into the noses of 44 volunteers — American prisoners — and then exposed them to temperatures of either 4°C or 32°C during infection, incubation, the peak of illness, and recovery. The authors concluded there were “no significant differences” in either the probability or the severity of infection between the chilled group and the warm group. A later summary of the literature was even more dismissive: by 1968, Texas researchers declared the case closed, writing, “Further studies seem unwarranted.”

Subsequent studies kept failing to find a link. Participants were chilled in climatic chambers, immersed in cold water, or inoculated and then cooled — and the cold did not reliably produce colds. The medical orthodoxy hardened: temperature and colds were unrelated, full stop. Grandmothers were simply wrong, and the persistence of the belief was chalked up to confirmation bias — people get sick in winter for all the behavioral reasons above, then blame the cold they happened to feel.

But a few researchers were never comfortable with how tidy that conclusion was. One of them was Professor Ron Eccles, director of the Common Cold Centre at Cardiff University, who suspected the earlier experiments had a design flaw: they inoculated healthy volunteers with virus and then chilled them. In real life, Eccles argued, colds circulate constantly through communities, and at any given time many people are carrying a low-level, symptom-free infection. Chilling might not help a virus take hold from scratch — but it might tip a silent infection into a symptomatic one.

The Cardiff foot-chill experiment

In 2005, Eccles and colleague Claire Johnson published a study in the journal Family Practice that tested this idea with a delightfully simple design. They paid 180 healthy students to participate. Ninety of them sat for 20 minutes with their bare feet in buckets of cold water. The other ninety — the control group — kept their feet dry in socks and shoes. Then everyone went home and recorded their cold symptoms twice a day for four to five days.

The result made headlines around the world. Thirteen of the ninety chilled students reported cold symptoms — runny noses, sore throats — in the days after the experiment, compared with five of the ninety controls. The difference was statistically significant. Eccles’s explanation: “When you dip your feet into cold water, you cause a pronounced constriction to the blood vessels in the nose. This is one of the factors we believe that actually can aid the virus by lowering the defences within the nose and triggering the symptomatic infection.”

His broader theory was that when colds are circulating, for every person visibly sick there are two or three carrying the virus without symptoms. Chilling constricts the blood vessels of the nose, shutting off some of the warm blood that delivers infection-fighting white blood cells — and a dormant infection flares into a real cold. “Although the chilled subject believes they have ‘caught a cold’,” the researchers suggested, “what has in fact happened is that the dormant infection has taken hold.” Eccles even speculated that a cold nose might be one of the major reasons colds are seasonal: “When the cold weather comes we wrap ourselves up in winter coats to keep warm but our nose is directly exposed to the cold air. Cooling of the nose slows down clearance of viruses from the nose and slows down the white cells that fight infection.”

It was a striking result — and it immediately attracted a serious criticism. Dr. Ronald Turner of the University of Virginia pointed out in an interview that the Cardiff experiment recorded symptoms, not actual viral infections. Nobody confirmed that the chilled students who felt sick were actually infected with a cold virus; some might have had allergic or irritant responses to the chilling itself. The study, its critics said, showed that chilling can make you feel as though you have a cold — not that it gives you one.

That objection kept the debate alive, and it set the stage for the most sophisticated investigations yet: laboratory studies that looked directly at what cold does to the immune defenses of the nose.

What cold air does inside your nose

The common cold’s favorite virus, the rhinovirus, has a well-known preference: it replicates more readily in the slightly cooler environment of the nasal cavity — roughly 33 to 35°C — than at the lungs’ core body temperature of 37°C. For years, researchers focused on how temperature affected the virus itself. Then a Yale-led team led by postdoctoral fellow Ellen Foxman and immunobiology professor Akiko Iwasaki asked a different question: what does temperature do to the immune response?

Published in 2015, their study examined airway cells from mice, comparing the innate immune response to rhinovirus at 37°C and at the cooler 33°C. “We found that the innate immune response to the rhinovirus is impaired at the lower body temperature compared to the core body temperature,” Iwasaki said. Crucially, the team also tested airway cells from mice with genetic deficiencies in their virus-sensing and antiviral machinery — and in those cells, the virus replicated happily at the higher temperature too. “That proves it’s not just virus intrinsic, but it’s the host’s response that’s the major contributor,” Iwasaki explained. In other words, the nose’s cooler temperature does not just suit the virus; it actively weakens the defense.

Seven years later, a Harvard Medical School and Mass Eye and Ear team found the mechanism in human tissue — and quantified it. Led by research fellow Di Huang with senior author Dr. Benjamin Bleier and collaborator Mansoor Amiji, the study asked how the nose’s front-line defenses respond to cold. The nose, it turns out, detects incoming pathogens and releases a swarm of billions of tiny fluid-filled sacs called extracellular vesicles, or EVs. These vesicles act as decoys: they present the virus with fake targets to latch onto instead of the receptors on real cells, while also carrying antiviral proteins.

The researchers first measured what cold air actually does to the nose: when volunteers moved from a 73.4°F room to a 39.2°F room, the temperature inside the nose fell from 98.6°F to 89.6°F — a drop of 9°F. They then exposed cultured human nasal cells to that same 9°F drop and watched the defense system falter on all three fronts: fewer vesicles released, weaker antiviral cargo inside them, and fewer decoy receptors. Overall, the number of vesicles released fell by 42 percent, and the antiviral proteins within them were impaired.

“There’s never been a convincing reason why you have this very clear increase in viral infectivity in the cold months,” Bleier said. “This is the first quantitative and biologically plausible explanation that has been developed.” The findings were published in December 2022 in the Journal of Allergy and Clinical Immunology.

*Physicians agree on the core fact: only viruses cause colds. The debate is about whether cold air makes you more vulnerable to them.*

Take these studies together and a coherent picture emerges — one that neither the grandmothers nor the debunkers fully captured:

1. Cold alone cannot cause a cold. No virus, no cold. The 1968 inoculation studies, the Mayo Clinic, and every infectious disease authority agree on this. Wet hair does not manufacture rhinoviruses.
2. But cold air measurably weakens the nose’s defenses. Chilling constricts nasal blood vessels, reducing the delivery of immune cells; cooler nasal temperatures impair the innate antiviral response (Yale, 2015); and a modest drop in nasal temperature cuts the release of virus-trapping extracellular vesicles by 42 percent (Harvard, 2022).
3. Chilling may convert silent infections into symptomatic ones. The Cardiff foot-chill study found that chilled volunteers reported cold symptoms at more than twice the rate of controls — consistent with Eccles’s theory that many of us carry subclinical infections that chilling can activate. The caveat, as critics note, is that symptoms were self-reported and infections were not virologically confirmed.
4. Winter’s main drivers remain behavioral and environmental. Indoor crowding, dry air that preserves viral droplets and dries protective mucus, and reduced sunlight and vitamin D all favor transmission. Cold-dampened immunity is one ingredient in the seasonal surge, not the whole recipe.

In short, the old warning confuses a contributing factor with a cause — and that confusion matters.

The Verdict

Verdict: Misleading.

The claim that going outside with wet hair or being out in cold weather gives you a cold is false in its literal form. Colds are caused by viruses — overwhelmingly rhinoviruses — transmitted through respiratory droplets and contaminated surfaces. Neither damp hair, nor a chilly wind, nor an open window can create a virus where none exists, and the classic experiments that inoculated volunteers and then chilled them found no increase in infection. On the central assertion, the doctors and the debunkers are right.

But the claim is not pure fiction, which is why “False” would be too blunt a verdict. Genuine, peer-reviewed research has established that cold exposure impairs the nose’s antiviral defenses: it constricts nasal blood vessels, dampens the innate immune response to rhinovirus, and slashes the release of virus-neutralizing extracellular vesicles by more than two-fifths. One well-designed trial found that chilling volunteers’ feet more than doubled the rate at which they developed cold symptoms in the following days. So while the cold cannot give you a cold, being cold can make you more susceptible to the viruses already circulating around you — and may even wake up a silent infection.

That is the anatomy of a misleading claim: a real phenomenon (cold weakens nasal defenses), a real correlation (colds peak in winter), fused into a false causal story (the cold caused my cold). Grandmother’s prescription — dry your hair, wrap up warm — is harmless and, at the margins, even directionally sensible. Her diagnosis of why it works was simply wrong.

What actually keeps you from catching a cold

If the goal is fewer colds rather than winning an argument with your grandmother, the evidence points to unglamorous basics. The Harvard researchers who uncovered the vesicle mechanism recommend the same precautions advised against far more serious respiratory viruses: wash your hands frequently, avoid touching your face with unwashed hands, and disinfect commonly touched surfaces. Ventilation and avoiding prolonged close contact with sick people matter more in winter precisely because that is when everyone crowds indoors.

Keeping your nose warm is not medical nonsense either — it is now arguably the one part of the folk wisdom with a laboratory mechanism behind it. A scarf over the nose on a bitter day will not guarantee anything, but given that a 9°F drop in nasal temperature measurably degrades your front-line antiviral swarm, it is a more rational precaution than it seemed a decade ago. Dressing warmly remains good advice; it was just never about the hair.

And the next time someone emerges from the shower, drips across the hallway, and gets the lecture — the honest answer is this: the wet hair is not the danger. The danger is the virus on the doorknob, the droplet in the crowded room, the hand that touched the face. The cold just holds the door open a little wider.

*Evidence-based medicine distinguishes the true cause — viral infection — from the folk explanation of cold and damp.* *Most people first meet the wet-hair warning as family lore, not science — checking the evidence is what turns lore into knowledge.* *Colds circulate in warm climates year-round. Winter does not create the viruses — it concentrates the crowding, dry air, and weakened nasal defenses they exploit.*