sickness sign of stress

Photo: Sam Edwards/Getty Images

3 of 7
All It Takes Is One Stranger's Sneeze and Suddenly You're Sick

Why it could be stress: Your immunity takes a hit when you're stressed, research shows, leaving you less capable of fending off whatever virus is making its way through your house or office. In one study, in Proceedings of the National Academy of Sciences, stressed-out people were twice as likely to get sick after being exposed to the common cold. The stressed folks also produced more pro-inflammatory compounds once the virus was in their systems, potentially making sniffles and sneezes worse.

Other possible causes: A consistent lack of sleep can also hamper your immune system. If you're sleeping well, not feeling stressed, but find that your sick-day tally keeps growing, ask your doctor whether a more serious issue could be to blame.