It’s a cycle any college study knows too well: Pre-holiday exams are nearly always followed by post-holidays colds. Recently,the team at Gross Science investigated this common occurrence and concluded the reason why we often get sick after finals is actually rather complicated.

To be fair, you’re not the first to have questioned if there was actually a connection between big exams and getting sick. In fact, scientists have dedicated many hours of research to get to the bottom of this. For example, in a 2009 study, researchers purposely exposed 153 healthy male and female volunteers to the cold virus in order to investigate who got sick and who didn't. Results showed the less you slept, the more likely you were to get sick. Since many college students spend the days before their exams pulling all-nighters, it’s likely this lack of sleep played a toll on their eventual poor health.

But it’s not just sleep that wreaks havoc on students’ immune systems; the stress of studying plays a role as well. Scientists recently examined the blood of medical students before and the day of their final exam and observed that the stress of taking the exam had a detrimental affect on their immune system.

In the end, it’s not exactly clear why we get sick following stressful exams, but its likely that the aforementioned lack of sleep and stress, as well as a generally poor college diet and lack of exercise play a role in the phenomena.