I have what I think is a cold sore in the corner of my mouth for the first time. Can you tell me what causes it. I have read that there are different types of cold sores.

Herpex Simplex is the virus that causes cold sores around the mouth. they can be passed from person to person, you can have had the virus for a long time, it is often triggered by being run down/stressed, sunlight, over indulgence in peanuts and chocolate.