How many of us have argued with our kids about wearing jackets when it’s cold out? How many of us have given up, thinking there’s probably no link between being cold and catching colds? Well, demographic studies have shown that the incidence of colds and flu increases during the winter [9, 21,23], and clinical studies show that cold exposure is associated with increased incidence and transmission of colds  and other diseases [7, 14, 15]. Why would temperature affect our ability to catch colds, since colds are caused by viruses? Recent studies suggest that the seasonality of colds is based on your nose . Yes, your nose. When healthy, the nose is an important gateway to your lungs and is responsible for clearing out viruses. In cold weather, though, the nose has been shown to function less efficiently [9,16], which is thought to increase our susceptibility to cold viruses. Exposing the body to cold temperatures also impairs nasal function [1,17]. So there is a scientific link between cold climates, cold exposure and more colds. Keeping our nose warm during winter months may be a difficult, but we can keep our bodies warm by wearing a jacket and bundling up. So the verdict is: your kids should wear their jackets! But I'd suggest putting a sign on the door reminding them, so that you don't have to stress out about it; stress increases your likelihood of catching a cold .
What the research says:
How many of us have argued with our kids about wearing jackets during the winter? There are many days when temperatures warrant covering up here in the Northeast, and on each of those days I say, “put your jacket on” at least once. I don’t know which is sadder: that my kids need to be reminded that often, or that I actually continue to remind them. But I persist because I don’t want them to catch a cold and you catch a cold when you don’t wear a jacket, right?
I’ve started to question that. Can you actually get sick from not wearing a jacket? Is there any scientific basis to that old wives’ tale?
How and when do people catch colds?
First let’s look at the incidence of colds. Does science back up the assumption that colds happen more in the winter. After reviewing the research, I found that, indeed, the incidences of colds, influenza, and other upper respiratory tract infections [URTIs] increase during winter months [9,23]. This is also true for other illnesses, including measles and chicken pox, both diseases caused by viruses that enter the body through the nose and upper airways [21,9]. So that definitely seems to support the need to wear a jacket.
But then I was reminded that colds are caused by viruses; more than two hundred different viruses in fact . To catch a cold (or exhibit the symptoms of the virus), the virus has to attach to your nasal lining. That normally happens when miniscule, virus-laden blobs of mucus go into your nose (through the coughs, sneezes and saliva of others, or by touching contaminated surfaces and then touching your nose). Once the blobs get to your mucus linings, voila: the viruses are in your system . So, you must be infected with a cold virus to catch a cold, and presumably you can’t get the virus from simply going outside without a jacket, or having wet hair when you walk outside in the winter.
But what explains the increased incidence of colds and other URTIs during winter months? One hypothesis is that the incidence of colds increases during colder months because disease transmission is increased. This is called the “crowding” hypothesis , and was proposed initially at the start of the 20th century . The scientific rationale of crowding is that people are crowded together in tighter spaces during the winter, so transmission of the virus is easier. However, many have questioned the validity of this hypothesis, observing that people who work in tight quarters throughout the year (like teachers or hospital workers), people who live in crowded cities, and people who regularly use mass transit also catch more colds in the winter. Why would they catch more colds in the winter if they exist in congested conditions all year round? The crowding hypothesis seemed flawed, so I went back to the drawing board.
Studies show a link between being cold and catching colds.
I did more research and found some interesting studies exploring the link between temperature and colds. Surprisingly, few studies have been done in this area, but their results seem to be consistent and may hold the key to answering the jacket question.
- Healthy people who put their feet in cold water for only 20 minutes caught more colds . In this study, healthy patients were asked to put their feet in a 50°F water bath for 20 minutes and were subsequently tracked for 4 to 5 days to see if they exhibited cold symptoms. Interestingly, only 9% of the controls reported having cold symptoms, while 29% of the people who put their feet in cold water had cold symptoms.
- Colds spread more effectively when temperatures and humidity are low . Researchers gave guinea pigs nasal drops containing the flu virus. Afterwards, infected guinea pigs were paired with healthy guinea pigs, and were housed in chambers at varying levels of humidity and temperature. Scientists founds that transmission of the flu was highest at low relative humidity (20-35%) and low temperatures (40°F).
- Hypothermia is linked to pneumonia [14, 15]. “Hypothermia is used to protect the brain, spinal cord and sometimes other organs from post-ischemic and post-traumatic injury” . When that is done, studies have shown that “pneumonia was one of the most frequent complications (48% of patients, a proportion markedly higher compared to those reported from intensive care unit patients), and that its prevalence increased with longer duration of hypothermia” [14,15]
So science supports a link between exposure to cold temperatures and catching a cold. But how? If viruses cause colds, how would climate affect your chances of getting sick?
The most obvious hypothesis is that exposure to cold temperatures lowers your body’s systemic immunity or ability to fight illnesses. But research by Castellani et al. has shown “there is no support for the concept that cold exposure depresses immune function” . Similarly, recent studies in animals and humans have shown that immune response is either unaffected  or enhanced [8,19,20] when people are exposed to cold temperatures. So there seems to be no consisent link between your systemic immune system and exposure to cold temperatures.
The scientific link between cold exposure and catching colds
More searching generated studies supporting a link between susceptibility to colds and seasonal temperatures [2,9], and the link goes through your nose. Yes, you read that right: the seasonality of colds seems to be based on changes happening in your nose. Here’s the proposed mechanism, as proposed by Eccles et al..
- You probably have the cold virus, even if you’re not sick. When healthy people were given cold viruses nasally, 80% of them became infected with the virus [2, 13]. Of the people who became infected, only 40% developed cold symptoms . That means, for every 100 people who have viruses associated with the common cold, only 40 will be symptomatic and the remaining 60 will exhibit no perceivable symptoms . So chances are the cold virus is lurking in your nose and the noses of those with no symptoms.
- Many of the viruses that are most relevant in the winter depend on your nose. Think back to how you catch a cold, and remember that colds (as well as flu, measles and chickenpox) are caused by viruses that enter your body through your nose and upper airway [9,21].
- Your nose is pretty important to your health. Our nose is an important gateway to our lungs, and it has a vital function. “The air we inspire is warmed and humidified as it passes through the nose, so that by the time it reaches the lungs it is fully saturated with water vapor and warmed to body temperature” . Your nose is also responsible for clearing out viruses using mucus, cilia and your immune system. Think back to those miniscule virus-laden mucus blobs. Particles like that are “trapped on the thin mucus blanket that covers the nasal respiratory epithelium and then slowly moved by rapidly beating cilia to the back of the nose, to be swallowed and then sterilized in the acid of the stomach” . So your nose is deceivingly important.
- Cold climates make your nose colder. During winter months, cold and dry air enters your nose, decreasing the temperature of your nasal epithelium .
- Your nose doesn’t work as well when it’s cold. When breathing in cold and/or dry air (as we often do during the winter), the clearing-out processes of the nose are impaired . The cilia in the nose beat more slowly, and the amount of mucus produced is decreased, making the nose less efficient at removing virus-laden blobs. Similarly, the immune processes that take place in the nose are impaired during cold weather 
- Not wearing a jacket can affect your nose [1,17]. In a study by Mudd et al., chilling the bodies of healthy patients caused “depression of the temperature of the nasal mucosa surface” and a “marked reflex vasoconstriction and diminution of blood supply” in the nose . So being cold can actually affect your nose in the same manner that breathing cold air can.
- When your defenses are weakened, you may be more likely to catch a cold . This is based on the assumption that “exposure to cold air will lower nasal respiratory defenses” so that the people with the virus but who haven’t developed a cold would start exhibiting cold symptoms . A cold nose can be the difference between just having the virus and actually catching a cold.
So, although this is simply a scientific hypothesis and hasn’t been proven, there are studies supporting the importance of your nose during cold season. Cold air and cold exposure compromises your nasal function, increasing the likelihood that viruses residing in your nose and upper airways will cause colds and other illnesses.
What does this all mean?
To put it simply, you are more likely to catch colds and other upper respiratory tracts infections when your body is cold. Researchers believe this may be mediated by changes in your nose, or, more specifically, changes in how effectively your nose can eradicate viruses. But whatever the mechanism, the fact remains that you are more likely to catch a cold when your body is cold and when it’s cold outside [1,7,14,15] so bundle up and have those you love bundle up!
One more interesting fact for parents. Stress increases your odds of catching a cold . In a study by Cohen et al., healthy people were surveyed to determine the level of psychological stress in their lives. Afterwards they were quarantined for 9 days, during which time they were given nasal drops containing common cold viruses. Stress increased both the number of people with the virus, as well as the number of people with colds. So stress not only makes you more susceptible to the virus, but also increases the odds that you’ll catch a cold from the virus. Keep that in mind if you stress out about your kids wearing a jacket. My solution: Post a sign by the coat closet that says, “Put on your jacket!” No stress for me. Jackets for them.
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