Is it safe to have oral sex when either partner has a canker sore — not a cold sore, but a canker sore? Does the same virus cause both and can you cause genital herpes with a canker sore?
— Blister Mouth
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. Where the sores in question are found and what they are caused by also set them apart: Canker sores appear more often under the tongue and inside the mouth than cold sores do (which are caused by the herpes virus). Canker sores may be sparked by stress, trauma to the area in your mouth, allergies and sensitivities, bacteria, and certain health conditions and diseases.
But, back to your question about sores in the mouth during oral sex: If the person performing oral sex has a canker sore in her/his mouth, and s/he comes into direct contact with her/his partner's semen, vaginal fluids, or blood, s/he may well be increasing her/his risks of contracting HIV from her/his 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. To reduce your risk of infection, avoiding oral sex when canker sores are present or using a condom or dam during oral sex to protect each other might be a good idea.
For more information on canker sores and oral sex, check out the related Q&As. Hope this helps!Alice!