(Oral Herpes · Fever Blister)

In this condition factsheet:

• The facts on Cold Sores


• Causes of Cold Sores


• Symptoms and Complications of Cold Sores


• Diagnosing Cold Sores


• Treating and Preventing Cold Sores

The Facts on Cold Sores

Cold sores, also known as fever blisters, are caused by a virus called herpes simplex. They usually appear around the mouth and on the lips. They are highly contagious but not dangerous.

About 90% of the population have been exposed to the virus by age 50. On average, people who get cold sores usually have 3 to 4 episodes a year, but this figure can vary significantly from person to person.

Causes of Cold Sores

The virus that most commonly causes cold sores is herpes simplex 1. However, in a minority of cases, herpes simplex 2 can also cause cold sores. About 50 to 80% of the people in North America have dormant (inactive) herpes 1 virus living permanently in their body.

The virus typically resides in a dormant state within the body's nerve cells. The body's immune system is normally able to keep the virus in its inactive state. When an infected person is exposed to a "trigger," or if the immune system is weakened, then the virus quickly multiplies and spreads down the nerve cell and out onto the skin, usually on the border between the lips and the face. This produces the characteristic tingling sensation and subsequent clusters of blisters.

Specific triggers include:

• cold weather
• fatigue
• fever, such as from stomach flu or other infections
• menstrual periods or other hormonal changes
• mental or physical stress
• physical irritation of the lips (e.g., following a visit to the dentist)
• sunlight or sunburn
• upper respiratory tract infections (i.e., common cold)

You can catch the virus if you come into direct contact with the cold sore blisters or the fluid inside them, which contains a high number of the viruses. This can easily happen through touching the hands of someone who has touched their blisters. It can also occur through sharing toothbrushes, cups, cutlery, face cloths, towels, lipstick, or other personal items that have been contaminated with fluid from the blisters. Once the blisters have stopped oozing or have crusted over, the person is no longer contagious.

Symptoms and Complications of Cold Sores

People who get cold sores may feel some unusual sensations around the lips in the 2 to 24 hours before the blisters appear, including tingling, burning, pain, or numbness. This is called a prodrome or warning sign that cold sores will appear at these spots. The skin then turns red and blisters form, generally varying in size from 0.5 cm to 1.5 cm. They ooze a clear liquid for a few days that dries to a yellow crust after a few days. There is usually some pain in the first few days after the cold sores break out, but this often disappears as the cold sore crusts over. Complete healing takes from 10 to 19 days for new infections, and 5 to 10 days for recurring infections.

The condition typically causes a cluster of lesions or blisters at a site around the lips. Areas other than the lips such as the inside of the mouth, around the nostrils, or even the surface of the eyes can also be affected. It is possible to spread the virus to other parts of your body if you touch the blisters and then touch yourself elsewhere. Cold sores inside the mouth can be problematic, interfering with talking and eating. If the virus infects the eye, it can damage the surface leading to vision loss. Very rarely, it can get into the brain, causing viral meningitis or encephalitis. The virus that causes cold sores, herpes simplex 1, can also be spread to the genitals during oral sex, leading to genital herpes.

Herpes simplex 1 never goes away completely, so cold sores can return later on if they are triggered again. Most cold sores don't leave scars; however, if an open blister becomes infected with bacteria or the lesions tend to return at the same site, scarring may result. People with weakened immune systems tend to get more cold sores and heal slower.