why do cold sores happen

Cold sores happen because of an infection with the herpes simplex virus, most commonly herpes simplex virus type 1 (HSV-1). After the initial infection, the virus stays in the body, hiding in nerve cells, and can become active again later, causing cold sores to reappear. Triggers for cold sore outbreaks include viral infections or fever, hormonal changes such as during menstruation, stress, fatigue, sun or wind exposure, and changes in the immune system. The virus spreads mainly through close contact like kissing or sharing items such as utensils, towels, or lip balm. Many people carry the virus without ever showing symptoms, but when it reactivates, cold sores form as painful fluid-filled blisters usually around the lips or mouth area.