Does getting cold give you a cold? What a chill can and can't do

Go out with wet hair, sit with cold feet, skip the hat, and you will catch a cold. Many people grew up hearing this. A chill cannot make a virus out of nothing, so on plain biology the saying fails: you have to meet the virus first. Yet a handful of studies find that temperature and colds move together anyway.

This article sorts the belief into three piles: what it gets right, what it gets wrong, and what is still open. It is informational material, not medical advice. If symptoms are severe, getting worse, or not improving, that is a question for a doctor.

What the belief gets wrong: a chill is not an infection

A cold is an infection. Rhinovirus is the best-known cause, and without exposure to a virus there is nothing to catch. Standing outside in a wet coat does not supply one.

The 2005 paper that tested foot chilling says as much in its background: previous clinical research "has failed to demonstrate any effect of cold exposure on susceptibility to infection with common cold viruses" (Johnson & Eccles, 2005). That is the authors' summary of earlier work, and it is the reason they ran their own experiment.

So the strong form of the folk belief, "cold air gives you a cold", is not supported. The weaker form is more interesting.

What the belief may get right: the foot-chill trial

Johnson and Eccles randomized 180 healthy people to have their feet chilled or to go through a control procedure. Everyone scored cold symptoms before, right afterwards, and twice a day for the next four to five days.

Right after chilling there was no acute change in symptom scores (P=0.62). Later, 13 of 90 chilled people reported having a cold, against 5 of 90 in the control group (P=0.047). Average total symptom scores over days 1 to 4 were 5.16 in the chilled group and 2.89 in the control group (P=0.013). The authors concluded that chilling the feet "causes the onset of common cold symptoms in around 10% of subjects who are chilled." They also noted that those who developed a cold reported more colds per year than those who didn't, so some people may be more prone than others.

Randomization is the strongest design for showing cause and effect. Here it still comes with limits that matter:

• Symptoms were self-reported. Nobody tested for a virus, so we don't know whether those were infections, or symptoms that felt like a cold.
• The P value for the headline result, 0.047, sits right at the edge of the usual cutoff.
• It is one study. The authors themselves wrote that "further studies are needed to determine the relationship of symptom generation to any respiratory infection."

Read it as a signal worth following up, not as proof that chilled feet cause infections. If the effect is real, it applies to roughly one person in ten, and the study can't say who.

What the belief may get right: falling temperature, outdoors, in a cohort

The next two studies are not experiments. They follow people through ordinary life and ask what the weather did before they got sick.

Both looked at 892 military conscripts in training in northern Finland, and the overlapping author lists and identical numbers suggest it is the same cohort. In the first analysis, 643 episodes of respiratory infection were recorded. The mean daily temperature before the infections was about −3.7 °C. Each 1 °C drop in temperature was associated with a 4.3% higher estimated risk of upper respiratory infection and a 2.1% higher risk of common cold. Lower absolute humidity was also linked to upper respiratory infections, and the average outdoor temperature fell over the three days before onset (Mäkinen et al., 2009).

That is an association in one population. It tells you that the infections clustered after colder days. It can't say why, and it can't rule out that something else changed along with the weather, such as how the conscripts were housed or trained.

A later analysis of the same cohort looked only at rhinovirus, with a case-crossover design: each person is compared with himself on days when he wasn't sick. There were 147 rhinovirus cases confirmed by PCR, a lab test for the virus. The mean temperature before infection was −9.9 °C, and each 1 °C decrease in temperature was associated with about 8% higher risk of rhinovirus infection. The authors' conclusion: "A decrease rather than low temperature and humidity per se during the preceding few days increases the risk of HRV infections in a cold climate" (Ikäheimo et al., 2016).

This is the most useful result for the question in the title. The infections here were confirmed in a lab, not just reported, and the signal was the change, not the cold. The authors read their data as pointing to the preceding few days of falling temperature rather than to cold as such. The limits are the same as before: one cohort, young conscripts, a cold climate, and an association. Whether it holds for a 45-year-old in a mild city is not something this study can tell us.

A review that agrees, with a caveat

A narrative review pulled together the older literature. Its summary: exposure to cold has often been associated with more, and more severe, respiratory infections. And "although not all studies agree," most laboratory and clinical evidence suggests that inhaled cold air, cooling of the body surface and a lowered core temperature produce responses such as narrowing of blood vessels in the airway lining and suppression of immune responses (Mourtzoukou & Falagas, 2007).

A review is a reading of other people's studies, so it can be only as good as they were, and the caveat is in the quote. It makes the picture a little more coherent, not much more certain.

A possible mechanism, in cells

One lab finding suggests why a cooler nose might matter. Rhinovirus replicated better at nasal temperatures (33 to 35 °C) than at 37 °C, and in mouse airway cells the antiviral response was weaker at the cooler temperature (Foxman et al., 2015). These were mouse cells in a dish. The details, and the findings that don't agree with each other, are in why we get sick more in winter, which is the better place to start if the mechanism is what you're after.

What nobody knows yet

• Whether any of this changes your own risk. The sources here observed cooling, or caused it in a trial. None of them tested a coat, a hat, dry feet or a warmer room. The evidence does not tell us whether staying warm makes a difference for you.
• Whether the foot-chill result repeats, and in what kind of infection. Self-reported symptoms with no virus test could be a cold, or something that feels like one.
• Whether the drop or the cold is what matters outside a Finnish barracks. The lab-confirmed result comes from one cohort of young conscripts.
• How the pieces connect. A narrowed blood vessel in the airway, a cooler nose and a drop in outdoor temperature are separate observations, made in different kinds of studies, and this article can't join them.

What you can look at in your own data

The app logs local outdoor weather (pressure, temperature, relative humidity, wind speed, UV index) next to your own symptom entries and Apple Health data, and looks for correlations in your own history with Pearson correlation, ANOVA and false-discovery-rate correction. Its nine fixed symptoms are headache, fatigue, drowsiness, dizziness, anxiety, irritability, nausea, joint pain and insomnia. Cough, sore throat and fever are not on the list. The app does not detect, diagnose or predict infections, so it cannot tell you that you caught a cold.

What it can show is whether stretches of falling outdoor temperature line up with more fatigue or poorer sleep in your own entries. That is a pattern about you and the weather, not about a virus. Weather sensitivity: what the science says explains why such a pattern needs care before you call it a cause.