Canker sores are not caused by an STD, cold sores are a form of herpes. If you have a cold sore and you perform oral sex on someone you can give them genital herpes.
Canker sores are caused by nutrition deficiency and stress. They are NOT contagious in any way and are not caused by any forms of STDs. The answer above describes a Cold Sore, often mistaken with...
Currently, it is unknown what the cause of canker sores is. It does not appear to be caused by bacteria nor virus, so it is theorized that there is a hereditary link. See the related link for more...