Does being cold make you sick?

"Winter is coming," and we all remember our parents telling us to "put a jacket on to go outside or you'll catch cold!" Of course, the common response is, "Don't be silly, being cold can't give you cold!" Or can it? Who wins this battle of beliefs?

The correlation between cold weather and sickness does stand out. Between 5-20% of Americans catch a cold or flu every year around late fall and winter. Not to mention, it's called a cold.

But there are some important things to consider. First and foremost: colds and the flu are caused by viruses. if there aren't any around, you won't catch a cold - no matter how cold you get. It's as simple as that.

So why the correlation with decreasing temperatures? Well for one, people tend to stay indoors much more often during the winter, which in turn, puts them in contact with more people. More people, means more exposure opportunities for the pathogens to spread.

On top of this, humidity plays a role in the spread of some viruses. As the humidity decreases in the winter, not only does the virus spread more readily, but the mucus in your nose dries out. Mucus would otherwise act as a protective barrier to pathogens. 

Finally, the lack of Vitamin D which we get from the sun, can affect  our immune system adversely. Both being inside more often, and the fact that winter has shorter days makes this a big factor for your health. 

So you've proven your parents wrong... right? Not so fast!

While some past studies have shown no correlation to temperature, recent evidence suggest otherwise. One study which put test subjects feet into ice water found that they were, indeed, more likely to develop common cold symptoms in the following days, than those who didn't. The developing hypothesis behind these results is that the cold temperatures cause blood vessel constriction, which slows the white blood cells from reaching the virus, ultimately inhibiting the immune response.

Cortisol levels, which pressures the immune system, are also increased with temperature induced stress. Furthermore, studies on both mice and human airway cells found that immune reaction to the common cold virus, in fact, temperature dependent. Warm infected cells are more likely to undergo programmed cell death, to limit the spread of infection. 

Finally, studies of the virus itself have revealed a secret weapon of sorts. In winter temperature, the virus's outer layer or envelope becomes much harder and acts like a shield. This allows it to spread from person to person much more easily. 

But at warm temperatures, this layer is more of a gel, which is not quite tough enough to protect the virus against the elements. As a result, its spreading ability is compromised. 

So, maybe your parents weren't so wrong after all. A happy compromise of going outside more often, bundled up, is likely to get you through the winter unscathed.