Can Canker Sores Cause Genital Herpes?

Cindy had a recurring problem with canker sores. It seemed like every time she drank orange juice, or accidentally bit the corner of her mouth, or ate a slice of her favorite sourdough bread her whole mouth would break out in tiny, grayish, painful sores.

These sores would ache day and night for about two weeks, until they would suddenly heal over and the pain would stop. When she got involved in a serious physical relationship, the question came to mind whether her canker sores were catching, and she could pass them on if she gave oral sex.

The simple fact is that canker sores are not contagious. The best explanation science has for canker sores is that they result from a triggering of the immune system by a non-infectious event.

The immediate cause of canker sores can be a sensitivity reaction to citrus or wheat products, or physical injury to the mouth, such as biting the side of the mouth or drinking hot coffee or tea, such as were problems for Cindy.

Canker sores can also be activated by braces, dentures, or losing teeth, or by abrasion to the mouth by toast, crackers, or chips. They are more common in people who have allergies to milk, and they are more common in people who use toothpaste and mouthwash formulated with sodium lauryl sulfate (SLS). They also occur when there is vitamin B1 deficiency, most common in heavy drinkers.

Can canker sores cause genital herpes, herpes genitalis, or any other kind of genital herpes blisters? The simple fact is that canker sores are not caused by infection. You can't give canker sores to someone else. And canker sores never appear on the genitals. Performing oral sex when you have canker sores will not cause genital herpes blisters, because there is no herpesvirus or any other microorganism to be passed to your partner.

Infections from your partner, however, are a different matter. Any kind of tissue injury, including canker sores, creates an easy path for the herpes virus to enter the body.

Canker sores can be infected with HSV-1, the primarily oral form of the herpesvirus, or HSV-2, the primarily genital form of the herpesvirus, or both. Once the infection becomes established in the lining of the mouth, it usually spreads to the throat, and can also erupt on the lips. When a sore inside the mouth is caused by viral infection, then it is possible to infect a partner through oral sex. But how can you tell the difference between canker sores and herpes?

Here are some key signs to look for:

• Canker sores have a yellowish, gray, or white appearance. Herpes-related sores are usually red.
• Canker sores are activated by physical injury to the lining of the mouth, or by eating certain foods. Herpes-related sores are activated by the immune system when it is stimulated by sunburn, infection, or medication.
• Canker sores recur every few weeks. Herpes-related sores recur every few months.

But either way, it's important to use barrier protection in oral sex. If you have canker sores, you need protection from your partner. If you have herpes infection, even if your herpes is not currently active, your partner needs protection from you. The less history you have with your partner, the more important it is to engage only in protected sex, with dental dams or condoms.

References:

Haisraeli-Shalish M, Livneh A, Katz J, et al. Recurrent aphthous stomatitis and thiamine deficiency. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. Dec 1996;82(6):634-6.

Mark KE, Wald A, Magaret AS, Selke S, Olin L, Huang ML. Rapidly cleared episodes of herpes simplex virus reactivation in immunocompetent adults. J Infect Dis. Oct 15 2008;198(8):1141-9.