What are cold sores?

Cold sores, sometimes called fever blisters, are clusters of small blisters on the lip and outer edge of your mouth. The skin around the blisters is often red and inflamed. The blisters can break open, weep a clear fluid, and then scab over after a few days. Complete healing may take 7 to 10 days.

What causes cold sores?

Cold sores are caused by the herpes simplex virus (HSV). There are two types of herpes simplex virus (HSV). HSV-1 usually leads to oral sores (herpes labialis), while HSV-2 most often leads to genital herpes. However, there is a link between the two types, as HSV-1 can result in genital sores and HSV-2 can result in cold sores if you come into contact with either virus.

Almost everyone has been infected with the HSV virus. Most people become infected with HSV for the first time during childhood (between the ages of 1 and 5) or young adulthood.¹ Between 60% and 90% of Americans have been infected with HSV and have HSV antibodies, while around 90% of people in underdeveloped nations have HSV antibodies.² You can be infected with HSV and have no symptoms.

The virus usually enters your body through a break in the skin around or inside your mouth. Up to 40% of the adult population in the United States has had a cold sore at some point as a result of being infected with HSV.¹ However, some people never develop cold sores even though they have been infected with HSV.

How are cold sores spread?

Herpes simplex virus (HSV) is most often spread by someone who is infected with the virus but has no symptoms (such as cold sores). It can also be spread from one person to an area of someone else's body by touching a cold sore or sharing things that a person who has a cold sore has used; a parent who has a cold sore often spreads the infection to his or her child. Common areas that can be infected with the herpes simplex virus include:

• The lips (herpes labialis).
• The genitals (genital herpes). Genital herpes most often develops after having sex with someone who has genital herpes. See the topic Genital Herpes for more information.
• The hands and fingers (herpetic whitlow). Herpetic whitlow most commonly affects health care workers. Plastic or rubber gloves can prevent its spread.
• The area where stools pass from the body (anus). This is called herpes proctitis.
• The eyes (herpes keratitis). A herpes infection of the eyes can cause blindness in some people.

Why do I keep getting cold sores?

Recurring infections can be triggered by factors such as stress, fatigue, sunlight, or another infection (such as a cold or flu).

After you have been been infected with HSV for the first time, the virus often retreats into the nervous system and stops causing symptoms (becomes dormant). On occasion, the virus may become active again and cause cold sores. Most people affected by cold sores will have 3 to 4 outbreaks per year.¹ A few people may have more than one cold sore attack per month.

Who is at greatest risk for developing cold sores?

Anyone who is exposed to the herpes simplex virus (HSV) is at risk for developing cold sores. However, some people may have the virus but may never develop cold sores.

People who have weakened natural defense (immune) systems are at an increased risk for having more severe and longer-lasting outbreaks of cold sores.

One form of HSV infection is seen most often in children 1 to 3 years old. This type of HSV infection (primary herpes stomatitis) can cause high fever and blisters throughout the mouth, which can interfere with the ability to eat. It can be serious in children—they can get quite sick from this illness, although they usually recover without any long-term problems.

Is there a cure or treatment for cold sores?

Cold sores can be treated if severe or if they cause you embarrassment or discomfort, but they will usually go away on their own within a few days. The herpes simplex virus (HSV) that causes cold sores cannot be cured. If sores recur, treatment can reduce the number and severity of outbreaks but cannot eliminate the infection.

Treatment may include topical creams or ointments or sometimes antiviral medicines (such as acyclovir or famciclovir). Treatment may lessen the duration of the cold sores by only 1 to 2 days, but can help soothe painful blisters or other uncomfortable symptoms.