Fever Blisters, Herpes Simplex

Herpes simplex is a virus. This virus causes fever blisters or cold sores. Fever blisters are small sores on the lips, gums, or roof of the mouth. People often get infected with this herpes virus but do not have any symptoms. The blisters may break out when a person is:

  • Tired.

  • Under stress.

  • Suffering from another infection (such as a cold).

  • Exposed to sunlight.

The blisters usually heal within 1 week. The virus can be easily passed to other people and to other parts of the body, such as the eyes and sex organs.


A virus, herpes simplex, is the cause of fever blisters. This virus can be passed (transmitted) from person to person and is therefore contagious. There are 2 types of herpes simplex virus. Type 1 usually causes oral herpes or fever blisters. Type 2 usually causes genital herpes. Both viruses do have the potential to cause oral and genital infections. However, the type 1 virus causes more than 90% of recurrent fever blister outbreaks.

Herpes simplex virus is highly contagious when fever blisters are present. Close contact, including kissing, can spread the virus. Children often become infected by contact with others who have fever blisters.

A child can spread the virus by rubbing the cold sore and touching other children or when other children touch clothing, wipes, or toys contaminated by an infected child with the virus. In adults, about 10% of oral herpes infections are from oral-genital sex with a person who has active genital herpes (type 2).

Type 1 herpes infection is very common, eventually occurring in up to 8 out of 10 otherwise healthy people. Most people become infected before they are 5 years old. The virus usually infects the lips, throat, or mouth. Initial infection in children can be extensive with many lesions throughout the mouth. In adults, the first infection may cause no symptoms. Some adults may develop many fluid-filled blisters inside and outside the mouth 3 to 5 days after they are initially infected but severe infection is uncommon. Fever, swollen neck glands, and general aches may occur but this is also uncommon. The blisters tend to come together and then collapse. When on the lip, a yellowish crust forms over the sores. Healing of the area without scarring typically occurs within 2 weeks.

Once a person is infected, the herpes virus permanently remains alive in the body within a nerve near the cheekbone. It then stays inactive at this site, only to sometimes travel down the nerve to the skin. This causes a recurrence of fever blisters. Recurrent blisters usually break out at the outside edge of the lip or edge of the nostril. Recurrent fever blisters may occasionally occur on the chin, cheeks, or inside the mouth.

Recurrent fever blister attacks are usually not as painful and not as numerous as the first infection. Recurrences are less frequent after age 35. Many people who have recurring fever blisters feel itching, tingling, or burning at the lip border. This can occur hours or a couple days before the blister appears.

Factors which weaken the body's immune system may trigger an outbreak or recurrence of herpes. These include some drugs (such as steroids), emotional stress, fever, illness, sleep deprivation, and other injuries. Sunlight may also trigger an outbreak. Many women have recurrences only during their menstrual period.


There is no cure for fever blisters. There is no vaccine for herpes simplex virus.

  • Certain medicines can relieve some of the pain and discomfort of the sores or promote more rapid healing. These include ointments that numb the blisters and medicines that control bacterial infections (antibiotics). A number of drugs active against herpes viruses (antivirals), either applied locally as a gel or cream, or taken in pill form, may promote healing by keeping the virus from multiplying and infecting more local tissue.

  • Keep fever blisters clean and dry. This helps to prevent bacterial invasion of the virally infected tissues.

  • Eat a soft, bland diet to avoid irritating the sores.

  • Be careful not to touch the sores and spread the virus to new sites, such as:

  • Other areas of the face.

  • Eyes.

  • Genitals.

  • Make sure you do not infect others. Avoid kissing people when a fever blister is present. Avoid touching the sores and then touching others.

  • Sunscreen on the lips can prevent recurrences if outbreaks are triggered by sunlight. The sunscreen should be put on before going outside and reapplied often while in the sun.

  • Avoid stress if this seems to cause outbreaks.


  • Only take over-the-counter or prescription medicines for pain, discomfort, or fever as directed by your caregiver. Do not use aspirin.

  • Do not touch the blisters or pick the scabs. Wash your hands often. Do not touch your eyes without washing your hands first.

  • Avoid close contact with other people, especially kissing, until blisters heal.

  • Hot, cold, or salty foods may hurt your mouth. Use a straw to drink. Eating a well-balanced diet will help healing.


  • Your eye feels irritated, painful, or you feel like you have something in your eye.

  • You develop a fever, feel achy, or see pus instead of clear fluid in the sores. These are signs of a bacterial infection.

  • You get blisters on your genitals.

  • You develop new, unexplained symptoms.


  • Understand these instructions.

  • Will watch your condition.

  • Will get help right away if you are not doing well or get worse.