Here's Why You Always Seem To Catch Your S.O.'s Cold

Photographed by Jessica Nash.
Misery loves company. No one understands this more than live-in couples who've braved cold season together (especially if kids are involved). A new study, published in the journal Nature Immunology, offers one reason why this chain reaction — first your S.O. gets sick, only to infect you — happens in the first place.
For the study, researchers tracked 670 participants' immune systems over the course of three years, looking for any kind of variation during that time. The composition of your immune system, which is made up of various kinds of cells circulating in your blood that are ready to attack intruders or pathogens when necessary, can change over time. Various factors, like diet, stress, sleep, and exercise, can influence this system. And the researchers found that we might be able to add who you live with to that list. In the end, they observed that people who lived with a child were found to have 50% less variation in their immune systems, compared to the difference between total strangers. In other words, sharing a living space with someone can cause your individual immune systems to resemble one another's.
Related: 12 Foods To Boost Your Immune System This Flu Season

It all comes down to environmental factors. Sure, about 25% of your immune system is determined by genetics, but the rest depends on what you regularly expose yourself to, from alcohol and smoke to those aforementioned lifestyle factors.

"A lot of these factors will be similar in couples, since they share an environment," says Adrian Liston, Ph.D, one of the study's researchers. So, if an illness or bug gets the better of your partner, it's fair to expect it'll befall you, too. On the bright side, this way, you'll always have a buddy to NyQuil and chill with.
Click through to Shape for more info on keeping yourself — and your relationships — healthy. (Shape)

Related: The Best Way To Start Exercising Again After Being Sick

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