What is a herpes simplex virus (HSV) mouth infection? 

Some people call it a cold sore, others a fever blister. Herpes simplex virus is the cause of this annoying and often painful chronic condition.

The herpes sores (lesions) typically last a week to 10 days. They most often occur on the lips, tongue, roof of the mouth, or the gums. The sores occur first as fluid-filled blisters that burst (rupture) after a day or 2. The sores will ooze fluid that has 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.

What causes an HSV mouth infection?

The virus is spread by skin-to-skin contact with someone who carries the virus. Most people with oral herpes were infected during childhood or as young adults from nonsexual contact with infected saliva. It can be passed by kissing, touching the infected person's skin, or sharing infected objects, such as lip balm, silverware, or razors.

The 2 most common forms of the virus are:

• Herpes simplex virus type 1 (HSV-1). HSV-1 is most often linked to infections of the mouth.

• Herpes simplex virus type 2 (HSV-2). This type is most often linked to genital herpes infections.

Having a cold sore doesn't mean that you have a sexually transmitted infection (STI). But both types of HSV can infect both the mouth and the genitals.

Once infected, a person will have the herpes simplex virus for the rest of their life. When the virus is not active, it is dormant in a group of nerve cells. Some people never have any symptoms from the virus while others have periodic outbreaks of infections.

It is not clear what triggers the virus to return. But the risk factors below may play a role:

• Long or intense exposure to sunlight

• A recent fever

• Emotional stress

• Menstruation

• Surgery

• Physical injury

Recurrent outbreaks are more common in the first year after the initial episode. After that, the outbreaks lessen in frequency and severity as the body builds antibodies to the virus.

What are the symptoms of an HSV mouth infection?

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

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

• Initial redness, swelling, heat, and pain, or itching in the area where the infection will erupt.

• Painful, fluid-filled blisters may appear on the lips or under the nose. These blisters, and the fluid they contain, are highly contagious.

• The blisters leak fluids and become sores.

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

The symptoms of an oral HSV outbreak may look like other conditions or health problems. Always see your healthcare provider for a diagnosis.

How is an HSV mouth infection diagnosed?

Herpes simplex virus may be difficult to diagnose because it may be confused with many other infections, such as allergic reactions. HSV can be confirmed only with a virus culture, blood test, or biopsy. A healthcare provider can often diagnose it based on where the blisters are and how they look. 

How is an HSV mouth infection treated?

Treatment will depend on your symptoms, age, and general health. It will also depend on how severe the condition is.

Treatment may include:

• Keeping the infected area clean and dry

• Antibiotic treatment for any secondary bacterial infections

• Topical antiviral creams

• Oral antiviral medicines

If you are applying topical medicine, be sure to wash your hands after touching cold sores. You can also use a cotton swab to apply medicine to the sore. This helps prevent the sores from spreading to other parts of your body or other people.

What can I do to prevent an HSV mouth infection?

These tips can help you prevent an oral HSV infection:

• Don’t have direct contact with someone with herpes sores. According to the CDC, genital herpes (HSV-2) can be contagious without any symptoms.

• Don’t share silverware, glasses, straws, lip balm, or other items with someone who has oral herpes.

• Don’t have oral sex if you or your partner have oral herpes (HSV-1). HSV-1 can be spread to the genitals, especially if you have oral blisters.

Key points about an HSV mouth infection

• A cold sore or fever blister is caused by the herpes simplex virus.

• The virus is highly contagious and can be spread by skin-to-skin contact, such as kissing.

• Once infected, a person will have the herpes simplex virus for the rest of their life.

• Herpes sores typically last a week to 10 days. They most often occur on the lips, tongue, roof of the mouth, or the gums.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new directions your provider gives you.

• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your healthcare provider if you have questions.