Science is Sexy: Why Do We Get Sick More in the Wintertime?

By Jimmy Rogers (@me)
Contributing Writer, [GAS]

Well it’s that time of year….of flu’s and rhinos (Rhinoviruses) and sniffles, OH MY! Yes, everyone seems to be getting sick. With all of these things going on, it might get you thinking…why now? Why do we always get sick more in the winter?  Well to answer that question let’s look at the conventional wisdom.  If you ask just about anybody off the street, they’ll tell you that the cold somehow weakens your body (maybe your immune system) and makes you more susceptible to disease.  How do they know this?  Well their mothers told them, of course!

Why Do We Get Sick More in the Winter?Everyone has heard the phrase “Bundle up or you’ll catch a cold!” But how accurate is that statement really?  Our body depends on an idea known as “homeostasis,” which describes the ability of a system to maintain itself.  While the outer temperature of your body varies widely based on environmental conditions, the core temperature remains constant.  Most people have a core body temperature of 98.6°F (37.0°C).  If you think about it, the only time that your temperature changes is when you have a fever.  Fevers only happen when the body specifically raises its temperature to fight off infections.

So how does this affect our initial question?  Well, if your internal temperature remains fairly constant in any weather, why does sickness increase in the winter?  Almost every microbiology course I’ve taken has posed this question, because it’s a good one to make you think scientifically instead of anecdotally (relying on “conventional wisdom”).

As it turns out, one of the other effects of winter is that people tend to stay indoors more often. When the population stays indoors (in a closed air system) and in the presence of others for an extended period, the rate of infection increases.  This is because at any given time, there are a few individuals infected with one of the many reoccurring (endemic) diseases.  If those people had only limited contact with others, they might spread their colds or they might not.  When they stay inside with everyone else, though, they successfully infect many more people.

While this answer may surprise some of you, I think the more impressive take-away is the regulatory ability of the human body.  Despite cold winds or a scorching sun, we maintain that core body temperature like it’s our job.  In some respects, it IS our body’s job.  All living things must find ways to maintain internal conditions such as temperature, pH, and sources of energy.  Without the existence of homeostasis, life as we know it would be impossible in our constantly changing world!

Have more questions on disease or homeostasis?  Leave a comment or ask me on Twitter and I’ll try to puzzle it out with you!





49 Responses to Science is Sexy: Why Do We Get Sick More in the Wintertime?

  1. In the colder weather, in order to maintain homeostasis (to stay warm) we shiver. Shivering causes us to expend energy, does this somehow weaken our immune system?

    • Hey “layman”

      Well, you’re right about the purpose of shivering. Because it uses up the body’s energy there is probably some strain on the efficiency of other systems. In general, though, unless you are really out in the cold without a coat for a long time, it’s unlikely you’re going to notice a lot of changes. If you think about it, how long have you really been out and shivering for a long time…it’s a natural warning to go get a coat or beside a cozy fire.

      In general, if you were to lose enough energy from prolonged exposure to the cold, you could have a lot more pressing worries than an infection like the cold (think hypothermia).

  2. In the winter, I get cracked lips a lot and sometimes a runny nose. Are these changes from just my body responding to the cold weather? Can the open sores on my lips make me more susceptible to getting sick?

    • Well there are two things at work here.

      A runny nose is caused by the body sensing either irritation or dryness and a need for more mucus. The cold air probably dries out your nose and the body naturally tries to moisten the nasal membrane.

      Chapped lips are also caused by cold, dry air. Chapped lips, as far as I’m aware don’t usually count as “open sores” but in more extreme cases where the lips crack, you can get some nasty sores. Any hole in your skin can result in an infection.

  3. so what is the difference between mono and rhino viruses? what effect to human’s health do they have? and which is more common? also vitamin D is for sure important in building strong bones, but does it really help our immune system?

    • Hey Phuong,

      Well mono is short for "mononucleosis," which is a disease that causes constant tireness. It is caused by the Epstein Barr virus (http://en.wikipedia.org/wiki/Epstein-Barr_virus).

      Rhinoviruses are a large group of viruses that are responsible for most common colds. Their latin prefix literally means "nose." You can guess what symptoms they all have in common (think runny).

      I'd Google something for the Vitamin D questions…I haven't a clue! :P

      • You have earned extra respect points from me for being willing to redirect and say "I haen't a clue!" Just remember that *after* they start calling you "Doctor" Jimmy. :) :applauds:

  4. Thanks for this, as it constantly comes up with my wife and I.

    What about the issue about getting wet and cold? That is, your feet get wet in a puddle when it’s chilly… I see no reason that should make me sick, yet she insists on it somehow. Similarly, if you go outside into chilly air with wet hair (e.g. after a shower), should that have any illness-related effects?

    • Glad you liked the article :)

      As far as I’m aware the actual act of having cold skin out in the cold air will not actually make you sick. Being very cold though can certainly use up a lot of energy and make you tired (as your body has to work to bring your core temp back to normal).

      When you get wet, it makes you colder faster. Essentially the fluid coats your skin and as air blows across it you get colder (try standing in front of a fan after a shower….). Sweating works on the same thermodynamic principle.

  5. In the colder weather, in order to maintain homeostasis (to stay warm) we shiver. Shivering causes us to expend energy, does this somehow weaken our immune system?

    • Hey "layman"

      Well, you're right about the purpose of shivering. Because it uses up the body's energy there is probably some strain on the efficiency of other systems. In general, though, unless you are really out in the cold without a coat for a long time, it's unlikely you're going to notice a lot of changes. If you think about it, how long have you really been out and shivering for a long time…it's a natural warning to go get a coat or beside a cozy fire.

      In general, if you were to lose enough energy from prolonged exposure to the cold, you could have a lot more pressing worries than an infection like the cold (think hypothermia).

  6. In the winter, I get cracked lips a lot and sometimes a runny nose. Are these changes from just my body responding to the cold weather? Can the open sores on my lips make me more susceptible to getting sick?

    • Well there are two things at work here.

      A runny nose is caused by the body sensing either irritation or dryness and a need for more mucus. The cold air probably dries out your nose and the body naturally tries to moisten the nasal membrane.

      Chapped lips are also caused by cold, dry air. Chapped lips, as far as I'm aware don't usually count as "open sores" but in more extreme cases where the lips crack, you can get some nasty sores. Any hole in your skin can result in an infection.

  7. so what is the difference between mono and rhino viruses? what effect to human's health do they have? and which is more common? also vitamin D is for sure important in building strong bones, but does it really help our immune system?

    • Hey Phuong,

      Well mono is short for "mononucleosis," which is a disease that causes constant tireness. It is caused by the Epstein Barr virus (http://en.wikipedia.org/wiki/Epstein-Barr_virus).

      Rhinoviruses are a large group of viruses that are responsible for most common colds. Their latin prefix literally means "nose." You can guess what symptoms they all have in common (think runny).

      I'd Google something for the Vitamin D questions…I haven't a clue! :P

  8. Thanks for this, as it constantly comes up with my wife and I.

    What about the issue about getting wet and cold? That is, your feet get wet in a puddle when it's chilly… I see no reason that should make me sick, yet she insists on it somehow. Similarly, if you go outside into chilly air with wet hair (e.g. after a shower), should that have any illness-related effects?

    • Glad you liked the article :)

      As far as I'm aware the actual act of having cold skin out in the cold air will not actually make you sick. Being very cold though can certainly use up a lot of energy and make you tired (as your body has to work to bring your core temp back to normal).

      When you get wet, it makes you colder faster. Essentially the fluid coats your skin and as air blows across it you get colder (try standing in front of a fan after a shower….). Sweating works on the same thermodynamic principle.

  9. Thanks for the article, this is something I’ve always been rather curious about.

    From what I’ve always understood, the answer is a lot more complicated than that. And that there are actually a large number of potential factors that create winter sickness. The other prominent reasons that I’ve read about are lower levels of vitamin d and that lower humidity allows viruses to live longer on surfaces that we may come in contact with. What are your thoughts on these and other factors? I’ve never read any studies on this subject, just news articles and google searches.

    I imagine that if it were primarily attributed to the time people spend indoors, that with the large shift in people’s leisure time over the past fifty years towards indoor activities (Internet, video games, TV etc) that infections now would be much higher. Are there any statistics that reflect this?

    My step father always insists that illness is caused when people go through large temperature shifts (such as from a warm house, to a cold outdoors). But it seems to be another bit of folk wisdom that I’ve not found substantiated anywhere. Though he still insists on it, despite my attempts to dissuade him on various occasions.

  10. Thanks for the article, this is something I've always been rather curious about.

    From what I've always understood, the answer is a lot more complicated than that. And that there are actually a large number of potential factors that create winter sickness. The other prominent reasons that I've read about are lower levels of vitamin d and that lower humidity allows viruses to live longer on surfaces that we may come in contact with. What are your thoughts on these and other factors? I've never read any studies on this subject, just news articles and google searches.

    I imagine that if it were primarily attributed to the time people spend indoors, that with the large shift in people's leisure time over the past fifty years towards indoor activities (Internet, video games, TV etc) that infections now would be much higher. Are there any statistics that reflect this?

    My step father always insists that illness is caused when people go through large temperature shifts (such as from a warm house, to a cold outdoors). But it seems to be another bit of folk wisdom that I've not found substantiated anywhere. Though he still insists on it, despite my attempts to dissuade him on various occasions.

  11. I read in the New York Times Science section last year about a study that found that the dry winter air is a better vector for viruses that in summer would drop to the ground rather quickly, but in winter float around longer and are more likely to be inhaled as a result. Sorry I have no citation for you, but this was a while back.

  12. Interesting that I just read about this in the past day or so…

    Seems that in the 1860s, Carl Wunderlich released data on the armpit, or axillary, temperatures of twenty five thousand people, and reported the mean to be 37.0 °C. Later authors converted this figure to degrees Fahrenheit, but introduced inaccuracies in the process, giving the traditional 98.6°F.

    But a study done in 1991 at the University of Maryland with much better instrumentation found a mean temp of 36.8 °C or 98.2 °F.

    The newer study also notes that a healthy individual’s temperature can vary during the course of a day by as much as 1.09°F, with the lowest point occurring early in the morning and the highest late in the afternoon.

  13. I read in the New York Times Science section last year about a study that found that the dry winter air is a better vector for viruses that in summer would drop to the ground rather quickly, but in winter float around longer and are more likely to be inhaled as a result. Sorry I have no citation for you, but this was a while back.

  14. Interesting that I just read about this in the past day or so…

    Seems that in the 1860s, Carl Wunderlich released data on the armpit, or axillary, temperatures of twenty five thousand people, and reported the mean to be 37.0 °C. Later authors converted this figure to degrees Fahrenheit, but introduced inaccuracies in the process, giving the traditional 98.6°F.

    But a study done in 1991 at the University of Maryland with much better instrumentation found a mean temp of 36.8 °C or 98.2 °F.

    The newer study also notes that a healthy individual's temperature can vary during the course of a day by as much as 1.09°F, with the lowest point occurring early in the morning and the highest late in the afternoon.

    • Good point. I'd heard about this before but I thought I had heard it was even lower than that.
      I feel like I run closer to mid 97 orally. Which is supposed to be higher than axillary.Of course I may only be checking it when I am feeling somehow off or expecting to be running a fever.
      But, as a nurse, I check a lot of temperatures (on typically healthy pregnant women) and they seem to run high 97 to low 98s orally most of the time.

  15. I read an article that said that the drier air in winter allowed droplets in the air from coughs to float much longer. A little humidity causes the droplets to increase in size and drop to the ground.

    Hence, diseases transmitted by coughs have better success in winter where indoor humidty is low.

  16. A recent study found that cold and flu viruses survive longer in cold, dry environments (your house in winter). This coupled with staying indoors probably leads to a much higher rate of infection. Best bet is to get a humidifier…

  17. “Staying indoors” is a hypothesis, not an explanation. There’s no evidence for it. And there’s some evidence against it — rhinoviruses (like the common cold) are more active in winter, even when adjusting for exposure.

  18. I read an article that said that the drier air in winter allowed droplets in the air from coughs to float much longer. A little humidity causes the droplets to increase in size and drop to the ground.

    Hence, diseases transmitted by coughs have better success in winter where indoor humidty is low.

  19. A recent study found that cold and flu viruses survive longer in cold, dry environments (your house in winter). This coupled with staying indoors probably leads to a much higher rate of infection. Best bet is to get a humidifier…

  20. "Staying indoors" is a hypothesis, not an explanation. There's no evidence for it. And there's some evidence against it — rhinoviruses (like the common cold) are more active in winter, even when adjusting for exposure.

  21. It’s definitely a lot more complicated than just because we stay indoors. Most of us work during the summer and stay in doors quite a lot then too. Another possibility is that the lack of sunlight, Less sun in winter, AND more indoors. means the human body isn’t getting the vitamins that the sun helps create, thereby weakening the immune system.

  22. Hey everybody, thanks for all the great comments.

    First off I’d like to mention that yes, many of you have correctly pointed out that this question (like so many in science) has a relatively complex answer. There are many factors at work in any disease, including passing the pathogen, invasion of the host, growth of the pathogen, and the notice of symptoms. Many of these ARE affected by temperature.

    I will say, in my own defense, that I was really hoping to dispel the myth that because “we” get colder our bodies somehow get sick. Homeostasis is the name of the game there. Now as someone pointed out, the nasal cavity becomes cooler and more susceptible to invasion in the winter, but no amount of bundling up will really help that problem (going back to the “bundle up or you’ll catch a cold” theory).

    Anyway, I’m glad so many people took an interest in this complex problem.

  23. It's definitely a lot more complicated than just because we stay indoors. Most of us work during the summer and stay in doors quite a lot then too. Another possibility is that the lack of sunlight, Less sun in winter, AND more indoors. means the human body isn't getting the vitamins that the sun helps create, thereby weakening the immune system.

  24. Hey everybody, thanks for all the great comments.

    First off I'd like to mention that yes, many of you have correctly pointed out that this question (like so many in science) has a relatively complex answer. There are many factors at work in any disease, including passing the pathogen, invasion of the host, growth of the pathogen, and the notice of symptoms. Many of these ARE affected by temperature.

    I will say, in my own defense, that I was really hoping to dispel the myth that because "we" get colder our bodies somehow get sick. Homeostasis is the name of the game there. Now as someone pointed out, the nasal cavity becomes cooler and more susceptible to invasion in the winter, but no amount of bundling up will really help that problem (going back to the "bundle up or you'll catch a cold" theory).

    Anyway, I'm glad so many people took an interest in this complex problem.

  25. The fact that we become ill more often in the winter has very little to do with staying indoors or cold weather EXCEPT that those things affect our ability to absorb Vitamin D. "Flu Season" occurs just when our bodies have run out of the Vitamin D stored in the summer, and tapers off as the days grow longer and warmer. Find more information on Vitamin D and its effects on illness at the Vitamin D Council website: http://www.vitamindcouncil.org. Dr. John Cannell has worked for many years to spread awareness of the severe Vitamin D deficiency that is epidemic in our world today. You probably are deficient in Vitamin D and don't even realize it (and by the way, it's actually a hormone, not a vitamin, and extremely important for good health). Take Vitamin D and stay well!

  26. The fact that we become ill more often in the winter has very little to do with staying indoors or cold weather EXCEPT that those things affect our ability to absorb Vitamin D. "Flu Season" occurs just when our bodies have run out of the Vitamin D stored in the summer, and tapers off as the days grow longer and warmer. Find more information on Vitamin D and its effects on illness at the Vitamin D Council website: http://www.vitamindcouncil.org. Dr. John Cannell has worked for many years to spread awareness of the severe Vitamin D deficiency that is epidemic in our world today. You probably are deficient in Vitamin D and don't even realize it (and by the way, it's actually a hormone, not a vitamin, and extremely important for good health). Take Vitamin D and stay well!

  27. The indoors hypothesis, while very interesting, doesn’t apply if you consider geographical differences. For instance, temperature in the caribbean only drops to 15C (59F) so the tendency to stay indoors is not as pronounced (Actually, it makes people get out more since it’s not as hot as usual) as it is further away from the tropics. However, “folk wisdom” in the caribbean still holds that people catch cold more easily during the “cold season”. Folk wisdom in Dominican Republic also states that you’re more likely to catch cold if you stay wet after being rained on.
    I’ve heard that what makes a person prone to “catch cold” is being exposed to swift changes in temperature but have no idea how that particular fact could elevate the probability of getting sick.
    On the other hand, it would be interesting to study if dryer-colder air makes a person more prone to sneeze (the nasal membrane can be irritated due to being dryer than usual) and therefore, more prone to spread diseases.

  28. The indoors hypothesis, while very interesting, doesn't apply if you consider geographical differences. For instance, temperature in the caribbean only drops to 15C (59F) so the tendency to stay indoors is not as pronounced (Actually, it makes people get out more since it's not as hot as usual) as it is further away from the tropics. However, "folk wisdom" in the caribbean still holds that people catch cold more easily during the "cold season". Folk wisdom in Dominican Republic also states that you're more likely to catch cold if you stay wet after being rained on.

    I've heard that what makes a person prone to "catch cold" is being exposed to swift changes in temperature but have no idea how that particular fact could elevate the probability of getting sick.

    On the other hand, it would be interesting to study if dryer-colder air makes a person more prone to sneeze (the nasal membrane can be irritated due to being dryer than usual) and therefore, more prone to spread diseases.

  29. Winter makes all of nature sick.  Trees go dormant, bears become unresponsive, birds fly away from it.  We know why these things happen.   it is caused by the spectrum of light reaching the earth.  In the winter, light has to pass through more atmosphere to reach the ground.  The atmosphere has minute droplets of water in it which refract the light like a prism.   Red light has a longer wavelength, so it continues in the original direction of the white light.   Blue light has a short wavelength, so it is scattered everywhere.   This is why the sky is blue, and sunsets are red.   Less Blue light causes trees to go dormant.   Birds migrate to where there is more blue light.   In extreme cases, people suffer Seasonal Affectiveness Disorder.  Blue Light is a therapy used to alleviate symptoms of S.A.D..   S.A.D. is characterized as having jet lag for 4 months.

  30. Getting less Vitamin D from the sun (your source of 90% of your daily need), in the winter likely plays a major role in both susceptibility to infection and also ability to recover. In addition to the physical environmental differences such as poor dilution of and repeat contact with airborne pathogens. Plenty of people are inside at work all day in all seasons, but I think because they aren't as inclined to go out and get some sun later in the day in the winter after work (where pathogen exposure is at a minimum, unless you have school age kids of course) they get less of this nutrient. Even if they did, the quality of the light is not as complete, (as insanity claus put it so well) so that would also do it. We are growing in our understanding as scientists and hopefully the general public as to precisely how a good diet and outdoor activity contribute to health in more than just the ways "mom used to say." In a lot of the cases, what people suspect about healthy things is true, sometimes its not. Be critical of the literature, but also be open minded (not directed at anyone, just a little advice when you search for health information).

  31. Shivering expends more energy than sweating, so if you are cold and working harder to maintain homeostasis when outside in the winter, that energy expended trying to maintain body temp is not available to help fight off the bacteria and viruses we come into contact with. Putting a coat on, eating fresh fruits and veggies, getting adequate sleep, and sunlight all play a role in a properly functioning immune system. Not to mention, the immune system is controlled by the nerve system, so making sure there is no interference there would be important. We see our chiropractor in addition to the above and are never sick in winter. It is awesome!