Cold sores, also known as fever blisters, are caused by a herpes simplex virus (HSV). There are two kinds of HSV: type 1 and type 2.

If you have cold sores or mouth ulcers, you may have herpes simplex virus 1 (HSV-1). If you have genital herpes, you may have herpes simplex virus 2 (HSV-2)—though type 1 can sometimes spread to the genitals and HSV 2 to the mouth through oral-genital contact.

According to the World Health Organization (WHO), 67% of people under age 50 have HSV-1, but only a minority of them get symptoms like fever blisters. Most people with oral herpes are infected in childhood. Once you're infected, the virus stays in your neurons and can be reactivated throughout your life.

Yes, you can infect someone else with oral herpes or genital herpes even when you're not having symptoms. But you're more likely to spread the virus if you have active sores or scabs.

There's no cure for cold sores, but you can treat an active infection with a short course of antiviral medication. When taken at the start of an outbreak, prescription cold sore medication can reduce the severity of your symptoms, shorten your outbreak, and lower your risk of spreading cold sores.

And if you experience more than 5 cold sore outbreaks a year, you might be eligible for daily antiviral medication, which can help prevent future herpes outbreaks.

Without treatment, cold sores usually scab over and heal within about two weeks.

Because recurring cold sores are caused by the reactivation of a virus, you can help prevent outbreaks by taking care of your immune system. Getting the recommended amounts of sleep and exercise, eating healthy food, and keeping your stress levels down can help defend your body against all kinds of illness, including HSV-1.

You can also help prevent cold sores by protecting yourself from too much sun exposure, and by keeping your lips moisturized when you visit the dentist. Both UV light and dental procedures can cause subtle lip damage known to reactivate HSV-1.

Your clinician may prescribe an oral antiviral medication like valacyclovir (Valtrex), famciclovir (Famvir), or acyclovir (Zovirax). The duration of treatment depends on whether you have an active outbreak or you want to prevent future outbreaks. Cold sore medications work best when taken within the first 3 days of symptoms.

Please note: This information is for general reference only. Your clinician will review your symptoms and health history to determine which (if any) treatments are medically necessary.