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At the school gate in October, somebody always says the same thing: wrap up or you will catch a cold. And its older sister, the one you hear in every hallway: do not go out with wet hair. Both are false, and they have been known to be false for sixty-eight years.
An adult gets two or three colds a year; a nursery-age child, six or eight. They are caused by a virus — more than two hundred different ones can do it, and the commonest is the rhinovirus, which travels on the droplets you release when you talk and on whatever you leave on door handles — and the symptoms that ruin your week are not made by the virus: they are made by you. The mucus, the tickle, the blocked nose and the headache are your own immune response at work. That is why a cold lasts as long as it lasts whatever you take for it, and why you can stand soaked at five degrees all afternoon and catch nothing, if there is no virus in front of you.
2015. Ellen Foxman and her team at Yale University publish in PNAS, the journal of the United States National Academy of Sciences, an experiment on mouse airway cells. Rhinovirus multiplies better at 33 degrees than at 37, and not because the virus likes the cold: it is that the immune defence of those cells is lazier when they are cool. The number that matters here is that 33 degrees is roughly the temperature inside your nose when you are breathing winter air. The headline that ran round half the world was "science confirms that cold gives you colds". The paper says something else: that if the virus is already inside your nose, a cold nose makes things slightly easier for it. You still need the virus, and a scarf does not cover the virus.
2005. The experiment everybody misquotes is by Claire Johnson and Ron Eccles at the Common Cold Centre of Cardiff University. A hundred and eighty volunteers. Ninety put their feet in a bowl of ten-degree water for twenty minutes; the other ninety sit with their shoes on. Four or five days later, thirteen from the bowl report cold symptoms, against five of the others. It looks like the grandmothers' definitive proof. The authors themselves explain that it is not: chilling closes the blood vessels in the nose, blood flow drops, and an infection you already had without noticing takes the chance to show itself. Nobody caught anything from the water. There was nothing in the water.
1968. R. G. Douglas, Keith Lindgren and Robert Couch publish in the New England Journal of Medicine, the reference medical journal in the United States, a paper whose title is already the result: exposure to cold environment and rhinovirus common cold, failure to demonstrate effect. They infected volunteers, split them between a normal environment and a cold one, and counted. Four of the nine in the cold fell ill and two of the seven in the warm, a difference far too small to mean anything.
1958. Harry Dowling, George Jackson and two colleagues at the University of Illinois recruit volunteers, put cold virus up their noses and then chill them thoroughly: two to four hours shut in cold chambers, at temperatures running from twelve below zero to fifteen above. Against them, an identical group kept warm. The proportion that catches cold is the same, and so is the severity. It has been in the American Journal of Hygiene since that year.
1946. Twelve years earlier, the British Medical Research Council had opened the Common Cold Unit in Salisbury, in an old prefabricated military hospital. It ran for forty-three years, until 1989, and some twenty thousand volunteers passed through it. The deal was famous in Britain: ten days in the countryside with expenses paid, in little flats for two, with food, books and a radio, in exchange for letting someone put drops up your nose that might carry a virus or might carry nothing at all. No going within nine metres of anyone who was not your flatmate. They tested the English version of the belief there, hair included: volunteers who got out of the bath and stood for half an hour, dripping and in wet socks, in a draughty corridor. They caught no more colds than anyone else. The unit also tested draughts, damp underwear, sleeping with the window open, and whole seasons of volunteers who were given no virus at all, to see how many caught cold by themselves: almost none. In forty-three years it published more than a thousand papers and never found the cure, which was what it was after. What it did find, in 1960, was the rhinovirus.
1773. A hundred and eighty-five years before the Illinois laboratory, Benjamin Franklin wrote a letter to Benjamin Rush, a Philadelphia physician. He doubted that wet clothes gave anyone a cold, it seemed to him that the causes of colds were entirely independent of damp and even of cold, and he held that people catch them from one another shut up in badly ventilated rooms. He had no microscope and no idea what a virus was. He had worked it out by watching who fell ill and where. And he acted on it in his own fashion: he rose early and sat naked in his chamber for half an hour or an hour, according to the season, reading or writing. He called it his air bath and said it had never done him the slightest harm.
The belief also leaves a mark you can see without a laboratory, because it is built into the language. In Spanish the illness is called resfriado and constipado, both from cooling; in English, a cold; in French, refroidissement; in German, Erkältung, which literally means a chilling. Half of Europe named the illness after the wrong cause, and did so centuries before anyone knew viruses existed. It is hard to argue with a whole language.
Colds really do arrive in winter, which is why the sentence never dies. The thing is that the cause is inside the houses: in winter we pack a lot of people into closed places with the windows sealed and the heating on, which is precisely the habitat a respiratory virus needs, and dry air dries out the mucous lining, the sticky carpet with which the nose traps what comes in. In the southern hemisphere the season falls in July, and in the tropics it rises with the rains, when people move indoors.
So this winter, when the child comes out of school with wet hair, dry their head if you like, but then do the three things that change the number: wash your hands when you come in, stop sharing a glass, and open the living-room window for five minutes every couple of hours.