A cold sore is a blister that typically appears on your lip or around your mouth. The herpes simplex virus type 1 (HSV-1) causes most cold sores. HSV-1 is very contagious. You can prevent getting cold sores by avoiding kissing people with them or sharing objects with them. Cold sores usually go away on their own within a couple of weeks.
A cold sore is a fluid-filled blister (or a cluster of blisters) that usually appears on your lip or around your mouth. They can also affect your cheeks, nose and chin. The herpes simplex virus type 1 (HSV-1) causes most cold sores.
Other names for cold sores include oral herpes, fever blisters and herpes simplex labialis. Even though people use the name oral herpes — and HSV-1 can spread to your genitals — HSV-1 isn’t the same as HSV-2. HSV-2 is the sexually transmitted virus that causes most cases of genital herpes.
A cold sore can develop multiple times a year or only once or twice in your lifetime. The frequency of an outbreak varies from person to person.
The virus that causes cold sores can infect people of all ages. Exposure to the virus typically occurs during childhood. Many people catch HSV-1 by the time they turn 5 years old.
It’s possible to develop a cold sore at any age, though the chance of having any outbreak decreases after the age of 35.
Cold sores are widespread. HSV-1 infects more than half of Americans between the ages of 14 and 49. However, many people never develop the sores or have any symptoms. About 20% to 40% of people who have the virus develop the sores.
Cold sores inside your mouth aren’t cold sores at all — they’re canker sores (mouth ulcers). Cold sores and canker sores look and feel similar, although canker sores can be quite painful. They’re both small, round sores that develop near your mouth. But canker sores only develop inside your mouth, including:
Canker sores have a variety of causes. But unlike cold sores, they don’t occur due to a virus, and they aren’t contagious. Causes of canker sores may include:
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Cold sores first look like small blisters that form around your lips and mouth. A cold sore on your lip usually only affects one side of your mouth. They can also show up on your cheeks, nose and chin. After two to three days, the blisters often start to ooze and then form a crust. Healing typically occurs within one to two weeks.
For many people, cold sore symptoms are more severe the first time they have an outbreak. You may experience the following cold sore stages:
Cold sores are sometimes called oral herpes because the herpes simplex virus type 1 (HSV-1) causes them. This virus is very common and highly contagious. It spreads through saliva or close contact — often through kissing or by sharing utensils, straws, towels or lip balm with someone who has a cold sore.
You may not know HSV-1 has infected you because the symptoms of exposure to HSV-1 are generally mild. After initial exposure to HSV-1, children sometimes develop a fever and small blisters inside and around their mouths.
After HSV-1 has infected you, the virus never goes away. It remains inactive (dormant) in a group of nerve cells in your face called the trigeminal ganglion. Because it can be dormant, some people aren’t aware they have the virus for months or even years after exposure.
When something triggers — or activates — the virus, it “wakes up” and travels through your nerves to your lips, where a cold sore develops. After an outbreak, the virus goes back to sleep in your body.
What triggers a cold sore in one person might not cause an outbreak in another person. Some people with HSV-1 never develop sores.
A variety of factors can activate a cold sore, including:
Yes, cold sores are highly contagious. They can spread easily from person to person through saliva or direct contact with a person who has one.
In healthy people, cold sores generally clear up on their own in one to two weeks. You’re contagious until all of the sores have scabbed over.
Although complications from cold sores are rare, they can include:
For certain groups of people, cold sores can lead to serious complications. The following groups of people should receive medical treatment immediately if they have a cold sore:
Your healthcare provider will probably be able to tell if you have a cold sore by looking at the affected area. They may also swab the sore to test the fluid for the herpes simplex virus.
If you’ve had one before, you’ll likely recognize the symptoms: a tingling sensation followed by redness, swelling and blisters on or around your lips. You can visit your provider for a diagnosis, although it’s not always necessary.
You can’t cure oral herpes. The goal of treatment is to heal the outbreak, but it can’t cure the virus. Once you have it, you have it for life.
Although it may take a while to get rid of a cold sore, some medicines can shorten the healing time and make the symptoms less painful. Cold sore treatment may include:
To avoid getting HSV-1, you should take the following precautions around people who have cold sores:
If you’ve already come into contact with HSV-1, take the following steps to reduce your risk of a cold sore outbreak:
If you have a cold sore, be careful around babies. Always wash your hands, and don’t kiss a baby until the sore has healed completely.
The majority of people who develop cold sores learn to live with and manage their outbreaks. They typically clear up quickly and have no lasting effects. However, in certain groups of people, cold sores can cause life-threatening infections. Newborns, people with eczema and people with compromised immune systems should see a provider right away.
In healthy people, cold sores usually clear up in one to two weeks.
While cold sores are uncomfortable, you can find relief at home. Suggestions to help manage them include:
You should seek treatment for a cold sore if you have:
A note from Cleveland Clinic
Once you contract HSV-1, you have the virus for life. Some people will never develop a cold sore, but others will experience regular outbreaks. Once a cold sore starts, it has to run its course. Although it can be bothersome, it typically goes away on its own within two weeks. If you develop a cold sore and have a weakened immune system or eczema, talk to your healthcare provider. They’ll help you determine the best treatment option and avoid complications.
Last reviewed by a Cleveland Clinic medical professional on 04/27/2023.
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