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Mouth Infections

What is the herpes simplex virus?

Some people call it a cold sore, others a fever blister, but this annoying and often painful chronic condition is caused by a virus: herpes simplex. About 50% to 80% of U.S. adults have oral herpes. According to the National Institutes of Health (NIH), by age 50, about 90% of adults have been exposed to the virus. Once infected, a person will have the herpes simplex virus for the rest of his or her life. When inactive, the virus lies dormant in a group of nerve cells. Some people never have any symptoms from the virus. Others have periodic outbreaks of infections.

How long do the herpes lesions last?

The herpes lesions typically last a week to 10 days. It most often occurs around the lips, oral mucosa, or tongue. The lesions occur first as fluid-filled blisters that rupture after a day or two. The sores will weep fluid that contains the virus. After a few days, the sores will form crusts or scabs. The virus is highly contagious and can be spread by skin-to-skin contact such as kissing.

The 2 most common forms of the virus are herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). HSV-1 is most often linked with infections of the oral cavity, with up to 90% of people in the U.S. exposed to this virus. HSV-2 is most often associated with genital herpes infections, with up to 30% of people in the U.S. exposed to this virus. However, both types of HSV can infect both the mouth and the genitals.

How can HSV infections be prevented?

Since HSV is spread through direct, physical contact, such as kissing and sexual contact, the best method of prevention is to avoid physical contact with the HSV sores when someone is having an outbreak. However, genital herpes can be contagious without causing any symptoms of the disease, according to the CDC.

What are the signs and symptoms of an oral herpes simplex virus infection?

The initial (primary) infection of the oral herpes simplex virus is usually the worst. It may cause severe, flu-like symptoms, swollen lymph nodes, and headache. However, some people have no symptoms at all. In the initial infection, sores can occur on and around the lips and throughout the mouth. 

Recurring infections tend to be much milder, and the sores usually erupt in the edges of the lips. Some people never have any more outbreaks beyond the initial infection. These are the most common signs and symptoms of a recurring oral herpes simplex virus infection:



  • The blisters leak fluids and become sores.

  • After about 4 to 6 days, the sores start to crust over and heal.

The signs and symptoms of an oral herpes simplex virus outbreak may look like other conditions or medical problems. Always see your healthcare provider for a diagnosis.

What causes the virus to recur?

It is not clear what triggers the virus to recur, but several factors are thought to play a role. Prolonged or intense exposure to sunlight, a recent fever, emotional stress, menstruation, surgery, or physical injury  might contribute to a recurrence of the virus. Recurrent outbreaks are more common in the first year after the initial episode, then lessen as the body builds antibodies to the virus.

How is an oral HSV infection diagnosed?

Herpes simplex virus is difficult to diagnose. Often confused with many other infections, such as allergic reactions, the herpes simplex virus can only be confirmed with a virus culture, blood test, or biopsy. However, a healthcare provider can often diagnose it based on the location and appearance of the blisters.

What are treatments for oral HSV infections?

Your healthcare provider will figure out the best treatment based on:

  • How old you are

  • Your overall health and medical history


  • How long the condition is expected to last

  • Your opinion or preference

Treatment may involve:

  • Keeping the infected area clean and dry

  • Antibiotic treatment for any secondary bacterial infections

  • Topical antiviral creams

  • Oral antiviral medicines

Online Medical Reviewer: Eakle, W. Stephen, DDS
Online Medical Reviewer: Kapner, Michael, DDS
Date Last Reviewed: 9/28/2015