What triggers cold sores to appear?

Cold sores are caused by the herpes simplex virus. Once the herpes simplex virus is in you, it can cause outbreaks of cold sores. Cold sore outbreaks are often triggered by exposure to hot sun, cold wind, a cold or other illness, a weak immune system, or even stress.

Do cold sores mean you have an STD?

Having a cold sore does not necessarily mean you have an STD. Most of the cold sores are caused by herpes simplex virus type 1 (HSV-1), which usually affects the lips and is not generally transmitted by sexual contact. Though less common, cold sores may be caused by another type of herpes simplex virus called HSV-2.