Does cold weather cause you to get sick?

If the question were, "Does cold weather cause you to get a cold or the flu?", then the answer would be: no, there is no scientific proof that it does. The studies so far have shown no cause:effect relationship between being wet or cold and having an infection by a common cold or flu virus.

There are connections made by some people through anecdotal evidence, since the viral cold and flu "season" is in the cold time of year. Cold weather isn't the reason more people can be sick with viruses then, though. The cold temperatures and flu/viral illnesses are merely concomitant. Those infections are coincidental to the lower temperatures, not a direct result of cold temperatures on the individual or their immune systems. It is not that the cold temperature will directly influence an increase in infection rates, it is just that they tend to be at the same time of year. (See the related questions for more information about why the flu has a season.)

There may be some indirect effect of cold weather keeping us indoors together more closely where we are more likely to spread viruses to each other. Also, the lowered amount of sunshine in the winter allows more viruses to be in the environment because there are fewer sun rays to "kill" them than in other times of year. When someone has a runny nose from a cold and then goes outside, the nose will usually produce more rhinorrhea (runny noses) allowing the spread of more viral infections, especially in children who are not as careful with hand washing and other preventive methods.

However, the question does not limit being "sick" to only infections, so the answer to this particular question is: yes, it can make you sick. Obviously, exposure to extreme weather conditions can make you sick and even kill you. But the cause of the sickness is the injury from exposure, not an infection by a germ.

Hypothermia can cause illness but just feeling chilly or even getting "goosebumps" or shivering from the cold weather is not hypothermia. When medical studies use that term, it is used to refer to a specific measurement of core body temperature. The term is not used just to mean that someone felt cold.

Hypothermia is not the same as being cold, it is a specific medical diagnosis and :
  • It is defined as a core body temperature that is at or below 95 F (35 C). The normal human core body temperature is 98.6 F (37 C).
  • Needs to be treated if core body temperature goes below 95 F (35 C).
  • Affects motor coordination through impact to the nervous system at core body temperatures of 95 F (35 C).
  • Becomes life threatening below core body temperatures of 90 F (32.2 C).
  • When the core body temperature drops that low, at the start of a hypothermic condition, symptoms can include intense uncontrollable shaking and shivering, then if your body continues to get colder, the shivering stops when the core temperature gets between 90 F and 86 F.
  • It causes heart rate, respiratory rate, and blood pressure to rise during the first stages of hypothermia as your body tries to increase metabolism and warm itself, but these vital signs fall once the core temperature gets 90°F (32.2°C).
  • Creates coma at below 86 F.
  • Heart rate becomes very irregular below 82 F and death can soon follow.

To catch a common cold or influenza, you need to be exposed to the viruses that cause those infectious diseases. It won't matter if you get chilly or go out for a few minutes without a jacket. That is an old belief from before we knew about germs that was due, in part, to the fact that colds and flu happen more in the cold weather.

While respiratory infections are caused by viruses and/or bacteria, there is some evidence that cold weather could increase the odds of getting sick, some of the proposed explanations are:
  • Dry air helps pathogens spread.
  • Dry air can reduce the layer of mucus which serves as protection in the respiratory tract.
  • Cold air can reduce the movement of cellular pili (used to move foreign bodies out) in the respiratory tract.
  • Cold-induced reduction of blood flow in some parts of the body may weaken the immune response in those areas (the body tries to preserve heat in the brain and internal organs subtracting blood from the rest).

However there is no conclusive research on this yet. See more information in the related questions.