Hi, how are you? For years now, I have been confused by cold sores and canker sores. My understanding it that canker sores occur only inside the mouth and are not contagious, while cold sores occur only outside the mouth and are contagious. I have heard that cold sores come from herpes and other sexually transmitted diseases, but am not sure if this is true.

When a person has blisters outside their mouth (usually on the lip or on the areas below their lips), what is it called? I'm not talking about diseases, but just common blisters. Are these called cold sores? Thank you in advance.