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Cold Sores

Also known as:  Fever Blisters, Herpes Simplex type I (HSV-1)

What is it?

Cold sores are small, fluid-filled sores that appear around the mouth and on the lips. They are called cold sores or fever blisters because they often occur during a viral illness, such as a cold.

Who gets it?

Anyone can get cold sores.

What causes it?

Cold sores are caused by the oral herpes simplex virus. The virus is spread through contact with someone with a cold sore. Once you have been infected with a form of the herpes virus, the virus continues to live in the nerve cells of the skin or the central nervous system, but doesn't cause any symptoms. Something, such as an illness, stress, sunburn, or injury, can cause the virus to become active again and cold sores to recur. Someone with cold sores can spread the herpes virus to the genitals through oral sex.

What are the symptoms?

Cold sores may begin with an initial tingling, burning, or numb sensation, followed by clusters of small, painful, fluid-filled blisters around the lips and surrounding skin. Within a few days, the blisters are covered with a thin, yellow crust as they begin to dry, and the pain subsides. The blisters are gone within one to two weeks, but are contagious until they dry up. Some people have only one occurrence of cold sores, while others get them repeatedly.

How is it diagnosed?

To diagnose cold sores, your doctor will study your medical history and perform a physical examination. Laboratory tests, such a viral cultures and blood tests, can be performed to determine the type of virus causing the symptoms.

What is the treatment?

Cold sores can be treated with an antiviral medication that reduces symptoms and dries up the blisters. People who get cold sores frequently or have severe outbreaks may take this type of medication daily to prevent symptoms. Topical creams, available by prescription and over the counter, may also reduce pain and help with healing. Over-the-counter pain relievers, such as acetaminophen or ibuprofen, can help reduce pain. Cool compresses on the affected area may also provide relief. It is important to keep your skin clean and dry so you don't develop any other types of infections in the blistered area. Your doctor might also prescribe some type of antibacterial ointment to help prevent infection.

Self-care tips

You can help prevent cold sores by avoiding contact with the blisters. Wash your hands frequently, do not share food or drink, and do not touch a blister then touch others or other areas of your body, especially the eyes or genitals. Use sunscreen and protective lip balm when outdoors to avoid sun-related outbreaks. As with any illness, it's important to get plenty of rest, follow a healthy diet, and reduce stress levels. People with a skin condition called atopic eczema should avoid any exposure to the herpes virus because it can develop into a possibly fatal condition called eczema herpeticum. Contact your doctor if your symptoms become worse or if the blisters appear to be infected.


This information has been designed as a comprehensive and quick reference guide written by our health care reviewers.  The health information written by our authors is intended to be a supplement to the care provided by your physician.  It is not intended nor implied to be a substitute for professional medical advice. 

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