The Facts
Cold sores - also known as fever blisters - are caused by a virus. They
usually appear on the lips. They are highly contagious but not dangerous. About
60% of the population have suffered cold sores at some point in their lives.
On average, people who get cold sores have two or three episodes a year, but
this figure can vary significantly from person to person.
Causes
The virus that causes cold sores is herpes simplex 1, a cousin of herpes
simplex 2, which causes the well-known sexual disease. About 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 nerve
cells of your spinal cord. 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 lips. This
produces the characteristic tingling sensation and subsequent clusters of blisters.
Specific triggers include:
- cold weather
- fever, such as from stomach flu or other infections
- menstrual periods
- mental or physical stress
- physical irritation of the lips (e.g., following a visit to the dentist)
- sunlight or sunburn
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. Once the blisters have stopped oozing or have crusted over,
the person is no longer contagious.
