You don’t get enough sleep

While you’re asleep, your body ramps up the part of your immune system that learns the best ways to attack new bacteria, viruses, and other triggers. If you aren’t getting enough sleep, though, your body doesn’t have the chance to fight diseases as effectively, according to a study in European physiology journal Pflugers Archiv. Just six days of restricted sleep could prevent your body from using a vaccination effectively, and other studies have shown lack of sleep makes it harder to kick a cold. Aim for seven or eight hours a night to keep your immune system at its prime.
You sit all day

Lack of exercise could make you sicker longer. Upper respiratory tract infections lasted 42 per cent longer in volunteers who worked out once a week or less than in those who did aerobic exercises five or more times a week, according to a study in the British Journal of Sports Medicine. The sedentary participants also had more severe symptoms. Squeeze in moderate exercise every day, like taking a quick walk during your lunch hour.
You feel lonely

Loneliness puts your body into fight or flight mode, according to research in the journal Proceedings of the National Academy of Sciences. The five-year study found that when people felt lonely, the hormone norepinephrine was higher. During crises, norepinephrine boosts production of the white blood cells that fight wounds. But in the process, it shuts down the virus-fighting part of your immune system, leaving you vulnerable to disease. If you’re feeling down, don’t wallow alone on the couch – ask a friend out for coffee or call a loved one for some support.
If loneliness is a problem, check out the 10 best emotional support dog breeds.