Updated: Aug 19
"Put on your jacket, otherwise you'll catch a cold!"
Have you ever wondered whether you can actually catch a cold from being cold?
Or, perhaps, contract COVID-19?
If you have, then this article is for you.
A simple scientific analysis reveals the true impact of cold—both natural and artificial cold—on the immune system.
It turns out the old cold folkore needs to be updated.
A Long Held Belief
On the Lookout for Viruses
General Cold Exposure (exposure to cold air and cold water)
Air Conditioned Rooms
Who Is Most Susceptible?
Why Do More People Get Colds in Winter?
1. A Long Held Belief
Throughout the clinical literature of the last three hundred years there are many reports that acute cooling of the body surface causes the onset of symptoms of upper respiratory tract infection.
Historically it has been generally accepted that acute exposure to cold is a direct cause of these symptoms. (1)
Indeed, use of the term "colds" may come from the common belief that cold exposure, in and of itself, causes upper respiratory tract infections (URTI). (2)
But that's not all:
Ever since the SARS-CoV-2 virus emerged, the belief has been that cold might also make you more susceptible to contracting COVID-19.
According to this belief, you can catch a cold during summer as well when you hang around in air-conditioned rooms. The same goes for COVID-19.
2. A Virus Infection
Cold symptoms can be caused by over two hundred different types of virus such as rhinoviruses, coronaviruses, RS viruses, influenza viruses, parainfluenza viruses, adenoviruses and enteroviruses. (1) The most common cold virus is the rhinovirus.
A cold or flu is a respiratory tract infection. Although COVID-19 is neither a cold nor flu, it is also a kind of respiratory tract infection.
3. The Effect of Cold Exposure on the Human Body
Experimental as well as anecdotal reports from late 20th century suggested that cold exposure increases susceptibility to virus infections. However, the majority of experiments were performed in mice and rats. (3)
Since humans are generally slightly bigger, have a less pointy nose, no tail, and have less body hair, these results can't be extrapolated to humans. They may extrapolate to human-rat mutants though.
Yes, human-rat mutants are very real.
Only in Japan 🇯🇵😁
The idea is to grow human stem cells in animals, to eventually create animals with complete human organs that could be transferred into a human body. (4)
Another reason why these studies aren't useful is that in many of the animal studies, cold water immersion was used as a stressor. (3)
Imagine a deformed giant picking you up and throwing you in a cold water tank. Similar to the rat, you'd probably be more concerned with your own survival.
What does that mean?
Some scientists may make use of various recreational drugs during working hours. This should be looked into. All jokes aside, we don't actually know the drugs they use.
What does modern science on actual humans say?
There is some evidence that cold exposure not only doesn't suppress your immune system, (2), (3) but may even stimulate your immune system instead, (5) thus making it less likely to contract a virus infection. (2)
In these studies scientists exposed people to cold air or had them immersed into cold water for short or extended periods of time, on one or multiple occasions, all the while laughing from the sidelines, presumably.
So far, this is the complete opposite from the common belief that cold makes you more susceptible to a virus infection.
Can you catch a cold from being in the rain?
It's not clear what the effects of walking around in wet clothes are, but it would presumably be somewhat comparable to cold water immersions. At the very least it is expected to be less harmful than is commonly believed, based on the evidence so far.
What else do we know?
The way we experience cold can also be affected by humidity.
Scientists, hopefully sober, looking into the combination of "cold and humidity" found that a decrease in temperature alongside a drop in humidity, could actually lead to an increased risk of contracting a virus infection, whereas higher humidity was not. (6)
So, is humidity perhaps the decisive factor?
They didn't study any random group of people though. They studied military conscripts, who have increased outdoor physical activity.
Why does that matter?
A combination of low temperature and low humidity can lead to the cooling and drying of the respiratory tract. During exercise you breathe more frequently, thus more chances of your respiratory tract cooling down and drying out. (6)
To be more precise, inhaling larger volumes of low humidity air while exercising, dries the mucosal membranes in the respiratory tract. (6)
The mucosal membranes moisten and protect the airways and function as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury. They do that by secreting a soothing, slippery substance called mucus. (7)
What else is interesting about that study is that, as soon as the temperature dropped below 0°C the risks weren't as high. (6)
Maybe that could be the reason that over-wintering in Antarctica does not appear to increase virus infection risk. (8)
Cold alone doesn't seem to be all-powerful in making you susceptible to virus infections. But with some help it may create the circumstances for viruses to settle down.
Just because there is a mouse in the room with a scientist, doesn't mean the scientist is going to submerge the mouse in water. He needs the help of alcohol and a bad study design to get the job done.
One of the reasons for the popularity is because of Wim Hof, also called the Iceman, who has exposed his body to the harsh and cold elements of nature on many of occasions.
Swimming underneath ice for 66 meters is a seemingly impossible feat, but apparently not for the Iceman. (9)
In one trial, hundreds of people were asked to test the effect of cold vs. hot showers.
As a result, to groups were formed:
A hot-shower group
A hot-to-cold-shower group
The people in the hot-to-cold-shower group could start out using hot water, but had to switch to cold water for the last 30-90 seconds of their shower.
This trial was done in the middle of an influenza epidemic, so the timing couldn't have been better to test out the cold shower hypothesis. (10)
What were the results?
Participants, who showered hot-to-cold for at least 30 days, self-reported a reduced sick leave from work. Contrarily though, there was no actual difference in illness days.
That's not all:
The participants were aware of the hypothesis, that the study aimed to verify:
"Cold showers might decrease illness and improve health." (10)
Obviously, there could have been a placebo effect involved.
We can't really say if cold showers have a protective effect against virus infections, but looking at the other evidence as well, at least it won't make you more susceptible either.
That means, you can likely take cold showers during pandemics without putting yourself at risk.
Though, be warned, men might experience some (in)visible side effects in the nether regions.
In this case, we don't mean losing your nerve and bailing out on someone.
Here we talk about having wet feet out in the cold.
So far we've only looked at cold exposure of the whole body.
There are, however, also beliefs that being outside with wet and cold feet can also increase your risk of getting sick.
That means, that either there are people that are more sensitive or susceptible or there's a 'nocebo effect'. This means a person is conditioned to expect a negative response, or anticipates negative effects from an experience. (12)
The participants were aware that the study was designed to investigate the effects of acute chilling on the development of common cold symptoms, so a nocebo effect can't be ruled out. (11)
A growing body of evidence is showing the nocebo effect, just like the placebo effect where one expects a positive outcome, is very real. (12)
Either way, it doesn't seem to have a huge impact. We don't really know what happens if you'd put your feet in cold water for extended periods of time, but we know that completely being immersed in cold water, like in the case of cold water swimmers, doesn't cause a weakened immune response.
In case you want to try it for yourself, don't jump in ice water straight away. The initial 'cold shock’ or 'WTH was I thinking', upon entering the water has resulted in most immersion related deaths, due to uncontrolled hyperventilation, which in turn leads to losing control over your body and gasping for air. (14)
Gasping for air is particularly unpleasant when your head is submerged in water, so better start out with cold showers.
Wet Hair and Headache
Are you doomed if you go outside with wet hair? Let's look into it.
We know that changes in weather can, in fact, cause headaches in some people. (15)
Maybe that's one of the reasons some people believe, that being outside with wet hair, is asking for trouble.
In some parts of the world, you can't even go to bed, without getting preached at by concerning family members, the moment they spot some H2O molecules on a strand of one of your hairs with their microscope-like super vision.
So what does the science say?
People who have frequent headaches or migraine attacks, seem to be more affected by cold weather than warm weather. (15)
This is not related to virus infections, however, and not all of us have migraines. But it's still possible to get a headache, even if you don't experience migraines.
Is a virus infection the culprit?
A virus infection is not the culprit, but there could be another mechanism at play.
When your hair is wet and it's chilly outside, or inside if you have an air conditioner switched on, the cold exposure results in heat loss.
The brain needs to be warmed and therefore brain cooling activity needs to be reduced. (16)
Some changes possibly take place in the sinuses surrounding the eyes and nose.
Mucus may accumulate to reduce the cold air within the sinuses. Also blood vessels could constrict to prevent heat loss. When this happens, you might experience a painful sensation behind the eyes or get a headache.
This could explain, getting a headache when you're not wearing any hat or let your wet hair dance around in the cold wind. (16)
There is no evidence, however, that this occurrence makes you more susceptible to virus infections.
It is often believed that cold air-conditioned rooms contribute to contracting a cold.
People sometimes complain about congestion or runny noses in air-conditioned rooms and they can sneeze more than usual.
Therefore, some people are concerned there is a link between the use of an air conditioner and COVID-19.
These cold and flu symptoms have nothing to do with viruses of any kind.
It all has to do with sinuses that can swell up. (17)
You've probably noticed, that after staying outdoors for some time in cold weather, your nose has a tendency to release some nasal fluid. If it's really cold you won't notice it until it's too late, and you end up tasting nasal liquid inside your own mouth.
A cold and runny nose is easily mistaken for virus symptoms.
Putting people in air-conditioned rooms for longer periods of time has not shown immune function to weaken inside a research setting. On the contrary, some immune markers actually improved. (2)
Whether going in and out of air-conditioned rooms frequently has any effect is not clear, with the exception of people with underlying conditions discussed further down.
Ironically, air-conditioned rooms may still put you at higher risk of contracting a cold or flu, but cold or temperature does not seem to be the reason.
The majority of virus transmission occurs within indoor and air-conditioned (relatively cold and dry) environments, which lots of different viruses seem to prefer. (18)
Air conditioned rooms are mostly closed environments, which are the perfect vehicle for airborne pathogens like viruses. (17)
Who is most susceptible?
There are people that are more sensitive to cold air. These are people with underlying health conditions, such as asthma and chronic obstructive pulmonary disease (COPD).
Exposure to cold air more easily irritates the respiratory tract, making people with asthma or COPD likely more susceptible to virus infections.
If there is a sudden change in temperature, like walking in or out of an air conditioned room,
it can also negatively affect their respiratory system. (17)
For this reason, it was expected that people with chronic respiratory diseases (CRD), such as asthma and COPD, would have an increased risk of a COVID-19 infection and more severe complications following an infection.
It has been a major topic of debate among patients with asthma during the pandemic. However, the prevalence of CRD’s among patients with COVID-19 might be lower than that expected. As of now, it remains a mystery why. It is speculated that there is a chance of under diagnosis or a lack of recognition, but it could also because the presence of a CRD elicits a different immune response.
Whether commonly used medications such as corticosteroids have a protective effect can also not be ruled out. (19)
To be on the safe side, anyone of us who has a chronic respiratory disorder should take extra care of themselves and their immune system.
Why do more people get colds in winter?
More respiratory infections occur during the winter, likely because more people spend time indoors, in closer contact to others. In the middle of cold and flu season, closer contact with other people increases the chance for viruses to spread. (20)
Can you catch a cold in summer?
Yes, colds can be contracted throughout the year. We also see that with COVID-19, which still lingers around during the warmer months of the year.
One thing that can happen during the summer months:
It's possible some people misdiagnose themselves as having allergies instead of a respiratory tract infection because they can sometimes have similar symptoms. (20)
Considering the total amount of evidence, the negative effect "cold" can have on your immune system doesn't seem to be as pronounced as is commonly believed.
A case could be made for being out in the cold amidst low humidity or dry air, especially while exercising or performing otherwise physical activities that induce heavy breathing. Therefore, intimate breathing sessions of moderate to heavy intensity should preferably be performed indoors.
A small number of people could be more susceptible to cold, but the nocebo effect could potentially play a role here too. If you really believe you'll get sick, it doesn't automatically mean you will, but it could increase your risk, especially if you let the thought or fear of getting a cold, frequently take hold of your precious awareness.
On the other hand, the placebo effect could also play a role and offer some protective benefits for certain habits you have that, on their own, may actually have little effect in making you more resistant to a virus infection.
Things like going outside with wet hair or being in air conditioned cooled rooms may cause symptoms of discomfort, but they are not linked to the effects of cold exposure.
What is clear, is that people with underlying conditions, such as asthma and COPD have a more fragile respiratory system and are more easily affected by cold. Paradoxically, the susceptibility to COVID-19 may be lower than anticipated, yet clear conclusions cannot be drawn.
All in all, cold has been an unsubstantiated fear for many.
Be that as it may, there are limits to what the human body can endure. Common sense is a valuable tool in your toolbox.
Don't go walking around in the snowy mountains in only your thong, unless you are the Iceman, who can physically repel Mr. hypothermia.
For most people though, regardless of the type of virus going around, the take-home message is: Don't be afraid of the cold.