Cold sores and fever blisters are caused by herpes simplex virus type 1 (HSV-1). This virus is passed from person to person by saliva (either directly, or by drinking from the same glass or cup) or by skin contact. Cold sores usually appear as clusters of tiny blisters on the lip. About 8 out of 10 people have the virus that causes cold sores. Most people are first infected before they are 10 years old.
After this first infection, the virus remains dormant (inactive) in the nerves of the face. In some people, the virus becomes active again from time to time. When this happens, cold sores appear. HSV-1 can get active again because of a cold or fever.
Stress also can lead to a cold sore outbreak. This includes mental and emotional stress, as well as dental treatment, illness, trauma to the lips or sun exposure. HSV-1 also can infect the eyes, the skin of the fingers and the genitals. Most genital herpes infections are caused by herpes simplex type 2 (HSV-2), however.
HSV-1 can cause serious illness in people who have other health problems. The virus also can cause serious illness in people whose immune systems are weakened by either illness or medicines they are taking.
People infected with HSV-1 for the first time may have fever, headache, nausea and vomiting. They may have painful swelling and open sores in the mouth. Some people have a sore throat. These symptoms usually begin about a week after someone is exposed to HSV-1.
Cold sores appear when HSV-1 is reactivated later in life. They may occur after a period of illness or stress, poor nutrition or sunlight exposure. Sometimes there's no known reason. Dental procedures that stretch the lip may occasionally trigger the virus.
The border of the lip is the most common place that these sores appear. They may occasionally occur inside the mouth, too. This is more likely in people who have weakened immune systems or other medical problems.
The first sign of a cold sore is a tingling, burning or itching. This is followed by swelling and redness. Within 24 to 48 hours, one or more tiny blisters ("fever blisters") appear. These blisters pop and form painful sores ("cold sores"). The sores eventually are covered by crusts, which look like scabs. The crusts are shed and form again while the sore heals.
Your dentist or physician usually can diagnose cold sores by asking you about your medical history and examining you. If you have other medical conditions, your physician may do other tests to diagnose cold sores. These tests are usually not necessary in healthy people.
When you are first infected with HSV-1, symptoms can last for 7 to 14 days. Cold sores usually crust within 4 days and heal completely within 8 to 10 days.
To help to prevent a first herpes infection in children do not let them be kissed by anyone who has cold sores, fever blisters or signs of a first herpes infection. However, HSV-1 is very common. Most children will be infected by the time they reach adulthood. Several different vaccines are being developed against HSV (types 1 and 2), but these appear to protect only people who have never been infected.
There is evidence that using sunscreen on your lips will prevent cold sores caused by sun exposure. Antiviral medicines may prevent cold sores from forming. In certain situations, your dentist or physician may prescribe these medicines. If you expect to encounter a known trigger, a medicine taken in advance can decrease the chance of a cold sore.
Some medicines can help cold sores heal faster. They also relieve pain and discomfort. The medicines are acyclovir (Zovirax), famciclovir (Famvir) and valacyclovir (Valtrex). These drugs cannot get rid of the virus. You need to take them each time you can feel a cold sore coming on. Once you have blisters on your lip, the medicines will not help much.
These drugs also can stop cold sores from popping up in the first place. Some people take them when they know they will be under stress.
Keep the area clean and apply lip balm. Try not to touch the area. Do not pick at the crusts over the sores. Avoid kissing anyone while you have blisters and sores. Cold sores can spread through kissing and by sharing things that touch the lips and the skin around them, such as spoons, forks, glasses and towels.
When to Call a Professional
Cold sores are common. They usually are not dangerous. If you have a weakened immune system (because of a disease, or because of medicines you take), HSV-1 can cause a serious illness. Call your dentist or physician right away if:
- Lip or mouth sores persist longer than one week
- The sores make it hard for you to talk or swallow
- You develop a fever
- You have a second outbreak of blisters
HSV-1 infection is a lifelong problem.