Free Don't Cross Your Eyes...They'll Get Stuck That Way!: And 75 Other Health Myths Debunked by Aaron E. Carroll

particularly unpleasant family of very similar viruses that cause runny noses, scratchy, sore throats, and general cold-related misery. With so many slightly different varieties, there are enough cold viruses to keep you getting sick again and again over the course of your life, without ever building up immunity to every single one. A new one can always come along and make you miserable with a cold once again.
    Even if it is the virus that makes you sick, you might still believe the cold weather plays a role in getting that virus. Does the cold hurt our immune systems and make us more susceptible to getting sick? Actually, the opposite seems to be true. In a study of how the body’s immune system reacts to cold exposure, the researchers actually found that the immune system was stimulated when people were exposed to the cold. The cold weather increased the number and the activity level of some of the body’s key sickness-fighting cells—the white blood cells (specifically, the leukocytes and the granulocytes for those of you who want to look for them under a microscope). Other chemicals that the body produces to fight infections were also increased. So, the cold weather actually may help your body to fight sickness! In this study, the researchers also looked at what would happen if you were warmed up first or exercised before your cold exposure. As it turns out, getting warmed up before you go out into the cold helps your immune system work even better. The infection-fighting cells and substances in your body increase even more if you are warmed up before you go out into the cold.
    Even though your body may have better sickness-fighting ability during the cold weather, it still seems like people get sick more often when it is cold outside, especially during the wintertime. The cause of the seasonality of colds (known to doctors as upper respiratory tract infections) is not entirely clear. One explanation is that people spend more time indoors when it is cold outside, staying in relatively close proximity to one another and allowing them to pass those colds around with their sneezing and coughing. Another idea that one expert suggests is that cold weather keeps the airways in your nose cooler, and this decrease in the temperature of the inside of your nose gets in the way of how the nose works to protect you from colds. Even though the rest of the body’s immune system seems to be activated by the cold weather, when the nose is exposed to cold temperatures, the tiny hairs and mucus that keep things moving out of your nose might not work as well. This could give the cold viruses a chance to settle in and make you sick. While these studies show how the cold theoretically hinders how well your nose works to protect you, there is not yet wide-scale evidence that this is the reason people get sick in the wintertime.
    There is a cycle of when certain viruses come and go. The rhinoviruses that cause most colds actually peak in the spring and fall, perhaps contributing to the belief that we get sick when the weather changes. Other families of viruses peak in the winter—viruses like those of the influenza family, which usually cause the much worse flu, or respiratory syncytial virus (RSV), which can make babies very sick and usually cause a cold in adults. We do not have a good explanation for why particular parts of the world see these viruses at particular times, but it is not necessarily the cold weather that brings them around. Don’t blame Frosty!
    Plus, it is important to remember that the practical effects of cold exposure on getting sick have been tested. When scientists test what the cold virus does in humans, there is no evidence that the cold weather makes you more susceptible to infection. In study after study where scientists put cold viruses directly into people’s noses and then measure who gets infected, the people who are forced to be in very cold conditions are no more likely to get infected with a cold than