10 Causes and Treatments for Cold Sores

Cause: Menstruation

Alright, the last cause on our list isn't one you can really control, at least not if you're female.

A woman's menstruation cycle can have an effect on the outbreak of cold sores, unfortunately, and it affects each person differently. Sometimes menstruation has no effect on women who have the herpes simplex virus-1, sometimes it does [source: Mayo Clinic].

There's really no way of knowing until it happens, so don't stress out waiting for your next period to arrive (remember, stress is a trigger too).