First, let's put to rest one of the most popular but most inaccurate rumors about running in the winter, the idea that you can freeze your lungs. This is a completely false rumor. The fact is that you can't freeze your lungs in any climate found in any populated parts of this planet. By the time the air you breathe in reaches your throat, just passing through your mouth warms it up to near your body temperature. By the time it passes through your windpipe and into your lungs, it is up to your body temperature. This doesn't mean that there aren't some side effects to breathing in this cold air but it is important to stress that there is no evidence that the side effects are long term dangers. The main side effect is that the cold air is very dry. As your body warms it, your body also has to humidify it. This can lead to a dry, raw throat and at times a dry cough after running. Some people claim that running in cold weather makes their lungs cold. The best explanation I can come up with is that the air they are breathing in is still dry when it gets to their lungs and their lung tissue may be drying out as it humidifies the air. This is not a long term problem, though, as your body tissues will recover with no long term damage once they are not being subjected to the dry air. Another popular myth about breathing in the cold air is that this will give you exercise induced asthma (EIA). While there is a lack of evidence that this won't happen, there is also a lack of evidence that this will happen. The most likely explanation is that breathing in the cold air increases the symptoms of mild cases of EIA enough to make themselves known, when running in warmer temperatures might not be enough for the symptoms to be noticeable or a bother. To prevent both the problems of breathing in dry air and causing a raw throat and possible onset of EIA symptoms, you could wear something over your face that covers your mouth. This will help you warm and humidify the cold air before it even gets to your throat.
