Cold Sores

Medically Reviewed By William C. Lloyd III, MD, FACS
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What are cold sores?

Cold sores, also known as fever blisters or herpes labialis, are painful, blister-like sores on or around the mouth caused by the herpes simplex virus (also known as HSV). Typically, they form on the lip, but they may also form on the chin, nose or cheeks, or inside the mouth. Often, a tingling, itching or uncomfortable sensation occurs in the area before blistering occurs. A solitary blister or clusters of small, painful blisters emerge that ultimately burst, scab over, and then heal. Once you have had an HSV infection, the virus resides in your body and can cause repeated outbreaks of cold sores in the same general location.

There are two types of HSV, type 1 and type 2. Generally, type 1 is associated with cold sores and type 2 with genital herpes; however, either type may cause sores in either the oral or genital region. HSV is very contagious and is spread by skin-to-skin contact, such as kissing or sexual contact, including oral-genital contact. HSV type 1 is very common. It is estimated that more than half of the people in the United States have been infected by the time they reach their 20s (Source: NIH).

Many people who have an oral HSV infection do not develop symptoms and may not even realize they are infected, while others develop large clusters of painful blisters. Currently, HSV infections are not curable, but self-care and medications can help relieve the symptoms of cold sores and decrease the number of outbreaks. To help reduce the spread of the infection, refrain from oral and oral-genital contact when symptoms are present.

Cold sore symptoms may be more difficult to control in people with a suppressed immune system, such as those who have AIDS (acquired immunodeficiency syndrome), are undergoing cancer treatment, or have had an organ transplant. Seek prompt medical care if you are unable to eat or drink due to the cold sores, if you have a suppressed immune system, or if the cold sores are near your eyes. Also seek prompt care for severely painful sores, sores that last more than two weeks, or frequent recurrences.

What are the symptoms of cold sores?

Symptoms of cold sores tend to be localized to the area of the outbreak and often follow a specific course, although the intensity varies from individual to individual.

Common symptoms of cold sores

Most cold sore symptoms are limited to the area of the outbreak and include:

  • Blisters on the lip, nose, chin or cheeks, or inside the mouth

  • Crusting or scabbing of the skin

  • Discharge or oozing from the sore

  • Fever

  • Localized tingling, itching or pain

  • Open sores (skin ulcerations)

  • Redness, warmth or swelling

Serious symptoms that might indicate a life-threatening condition

Cold sores that interfere with your ability to eat or drink can lead to serious complications such as dehydration and, in people with diabetes, low blood sugar (hypoglycemia). Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms including:

  • Change in level of consciousness or alertness, such as passing out or unresponsiveness

  • Change in mental status or sudden behavior change, such as confusion, delirium, lethargy, hallucinations and delusions

  • Excessive thirst

  • Not producing any urine, or an infant who does not produce the usual amount of wet diapers

  • Seizure

What causes cold sores?

Cold sores are caused by the herpes simplex virus (HSV). Two types of the virus exist, type 1 and type 2. Cold sores are most commonly caused by HSV type 1, but they can also be caused by type 2. Herpes infections are very contagious and are spread by skin-to-skin contact. It is possible to spread the virus even if cold sores are not present, and not all people who have been infected with it will develop symptoms.

HSV is commonly spread through oral contact, such as kissing, but it can also be spread by oral-genital contact. Herpes simplex viral infections are most contagious during an outbreak, including the time right before the blisters start to form. During this time, a tingling or uncomfortable sensation may be felt in the area. Cold sores are single lesions – you get one at a time. When cold sores recur they usually do so at the same location and always on the same side of the body (right or left of midline). Recurrent lesions that migrate or appear in multiple numbers are probably not cold sores.

Once you are infected with HSV, the virus resides in your body and can reactivate and cause recurrent cold sores. A number of environmental factors may trigger these recurrences, including stress, illness or infection, trauma, excessive sun exposure, or exposure to cold.

What are the risk factors for cold sores?

A number of factors increase the risk of developing cold sores. Not all people with risk factors will get cold sores. Risk factors for cold sores include:

  • Oral contact with someone who has an oral herpes infection

  • Oral-genital contact with someone who has a genital herpes infection

  • Sharing eating utensils, cosmetics, or toothbrushes with someone who has an oral herpes infection

  • Young age

Reducing your risk of cold sores

You can lower your risk of developing cold sores by:

  • Avoiding oral contact with anyone who has cold sores

  • Avoiding oral-genital contact with anyone who has active genital herpes

  • Avoiding sharing eating utensils, drinks, and other items that come in contact with other peoples’ mouths when they have cold sores

  • Avoiding triggers for cold sores, such as excessive sun exposure, stress, trauma, exposure to cold, or illness

How are cold sores treated?

Currently, cold sores cannot be cured; once a person is infected with herpes simplex virus, it does not go away. People who develop cold sores may continue to have periodic outbreaks. Between outbreaks, the virus resides in the nerves of the face. When the virus is reactivated, another outbreak of cold sores occurs, typically in the same place as the original cold sores.

The goal of treatment is to reduce symptoms and potentially to reduce the duration of the outbreak. Topical medications can be used to shorten the healing period of the sores; however, these medications need to be started when symptoms first develop, and they shorten the healing period only by about a day.

Topical medications for the treatment of cold sores

Topical medications used to shorten the duration of cold sores include:

  • Acyclovir (Zovirax)

  • Docosanol (Abreva)

  • Pencyclovir (Denavir)

People who have severe or frequent outbreaks and those whose immune systems are suppressed can be prescribed oral antiviral medications to reduce the number of outbreaks. Oral antiviral medications can also be used to treat active cold sores in people who are immunocompromised.

Oral antiviral medications for the treatment of cold sores

Oral antiviral medications used to reduce the frequency of outbreaks of cold sores include:

  • Acyclovir (Zovirax)

  • Valacyclovir (Valtrex)

Occasionally, the sores can get infected by bacteria. If that happens, antibiotics may be used to treat the secondary infection.

What you can do to improve your cold sore symptoms

In addition to taking medication to shorten the duration or reduce the frequency of cold sore outbreaks, you can reduce your risk of outbreaks and manage your symptoms by:

  • Applying ice or heat, such as a warm, moist towel, to the affected area

  • Avoiding picking at the sores

  • Avoiding triggers for cold sores, such as excessive sun exposure, stress, trauma, cold exposure, or illness

  • Taking over-the-counter pain relief medications, such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin)

  • Using over-the-counter pain relief ointments, gels or creams that contain ingredients such as benzocaine or lidocaine

  • Using soothing and protective agents to protect the cold sores once the blister has broken, such as lip balms or products with allantoin, dimethicone, camphor or petrolatum

  • Wearing sunscreen

If you have cold sores, it is important to practice good hygiene to avoid spreading the infection to those who have close contact with you. Do not try to squeeze or pop the blister and don’t pick at the cold sore while it is healing. Wash your hands frequently with soap and water and avoid sharing eating utensils, drinks, and other things that come in contact with your mouth until your infection has cleared.

What are the potential complications of cold sores?

Cold sores usually clear up on their own without any complications. However, cold sores that occur near the eyes pose a risk of eye infections. Occasionally, cold sores can hinder your ability to eat or drink, which can make it difficult to keep hydrated and can interfere with blood sugar control if you have diabetes. Left untreated, cold sores near the eyes and those that interfere with drinking and eating can cause serious complications. You can help minimize your risk of serious complications by following the treatment plan you and your health care professional design specifically for you.

Complications of cold sores include:

  • Dehydration (loss of body fluids and electrolytes, which, left untreated, can be life threatening)

  • Scarring

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 16
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Cold sores. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/coldsores.html
  2. Genital herpes - CDC fact sheet. Centers for Disease Control and Prevention. http://www.cdc.gov/std/herpes/stdfact-herpes.htm
  3. Bernstein DI, Bellamy AR, Hook EW 3rd, et al. Epidemiology, clinical presentation, and antibody response to primary infection with herpes simplex virus type 1 and type 2 in young women. Clin Infect Dis 2013; 56:344.