A cold sore (fever blister) is a small sore or blister on the lip. Sometimes it's inside the mouth. Most cold sores are caused by herpes simplex virus type 1 (HSV-1). The virus spreads easily from person to person. It can enter the body through a break in the skin, such as a cut or scrape. It can also enter through mucous membranes such as the lips or mouth. Many people have the virus in their body. They are often first exposed to the HSV-1 in childhood. But not everyone who has HSV will get a cold sore. In some cases, cold sores can be caused through sexual contact by HSV type 2 (HSV-2). HSV-2 is the more common cause of genital herpes. But it can sometimes cause sores on the lips or in the mouth.
A cold sore starts as 1 or more painful blisters on the lip or in the mouth. The blisters break open and crust. They often go away in a week. The first time you have a cold sore, the symptoms are often more severe. You may have a fever as well as mouth and throat pain. After the cold sore goes away, it can come back in the same spot. This is because the virus stays in the body. But after the first outbreak, other symptoms such as fever are often mild. Or they don’t come back.
Home care
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If you have been prescribed antiviral medicines, take these as your healthcare provider directs. You may use over-the-counter medicine as directed.
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Putting petroleum jelly on a sore using a disposable cotton swab may help ease pain. Ask your provider before using any other creams or ointments.
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For severe pain, wrap an ice cube in a cloth. Apply it to the sore for a few minutes at a time. Or rinse your mouth with a glass of warm water mixed with a teaspoon of baking soda to ease pain.
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Don't eat acidic foods such as citrus fruits and tomatoes.
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Don’t touch the cold sore. The virus can cause a sore on the finger. It’s very important not to touch the sore and then touch your eyes. The virus can spread to the eyes.
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Don't kiss other people.
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Don't share eating utensils, lip balm, razors, or towels.
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Wash your hands after touching the area of a cold sore. The herpes virus can be carried from your face to your hands when you touch the area of a cold sore. When this happens, wash your hands well, for at least 20 seconds. When you can’t wash with soap and water, use an alcohol-based hand sanitizer.
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Disinfect things you touch often, such as phones and keyboards.
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Use condoms to help prevent passing on the viruses through sex.
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Don’t have oral sex.
Follow-up care
Follow up with your healthcare provider, or as advised.
When to call your healthcare provider
Call your healthcare provider right away if you have any of these:
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Fever of 100.4°F (38°C) or higher, or as directed by your provider
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Pain that gets worse
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You can’t eat or drink because of painful sores
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Blisters spread beyond your mouth or lip to parts of the chest, arms, face (especially the eyes), or legs
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New symptoms
