Oral sex with canker sores

Dear Blister Mouth,

Canker sores have not been proven to be caused by a virus, and they are not contagious, or a sign of any other disease. However, if the person performing oral sex has a canker sore in his/her mouth, and s/he comes into direct contact with his/her partner's semen, vaginal fluids, or blood, s/he may well be increasing his/her risks of contracting HIV from his/her partner if s/he is infected. Any type of lesion or opening in the mucous membrane of the mouth makes transmission of HIV more viable than if the lesion weren't there. You'll need to make decisions about how much risk you want to take with your partner -- if you want to be extra safe, avoid oral sex when canker sores are present, or use a condom or dam during oral sex to protect each other.

For more information on canker sores, see Alice's archived answers to Cold sores vs. canker sores -- Oral sex risks?, Cold sores + oral sex = Genital herpes?, and Fever blisters on lips. For more information on oral sex and HIV, see Alice's archived answers to HIV-passive oral sex? and Risk of oral sex with no ejaculation?.