Cold Sores

Cold sores, also called fever blisters, are small, sometimes painful blisters that can form on and around the mouth. The medical term for cold sores is oral herpes because they are caused by the herpes simplex virus (HSV).

Herpes simplex virus 1 (HSV-1) is very common. In fact, It is estimated that nearly 90% of adults in the United States have been infected with it by age 50 (although not everyone gets cold sores).

This article will explain the symptoms of cold sores, what causes them, how they are treated, and how to prevent outbreaks.

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Close-up of woman's lips with cold sores

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Symptoms of Cold Sores

Many people who have HSV-1 never experience any symptoms. If you do have symptoms, they may include:

  • Fluid-filled blisters on the outside of the mouth around the lips
  • An itchy or tingling sensation in the area shortly before the blisters appear
  • Fever and swelling of the lymph nodes, similar to other viral infections (though these symptoms are less common)

The blisters may be confined to one area only or appear in several areas at a time. They typically last from seven to 10 days, during which time they will break open, ooze fluid, and form a crust before healing.

Are Cold Sores Contagious?

HSV-1 can infect another person during the time the cold sore is active. You can catch the virus if you touch someone's open sore or something that has been in contact with the virus, such as cutlery or toothbrushes. However, this doesn't mean you will get cold sores since the virus can be asymptomatic.

Causes of Cold Sores

Most cold sores are caused by the HSV-1 virus, and most people who get the virus are exposed during infancy or childhood through skin-to-skin contact with an adult with the virus, though it is possible to be infected during adulthood as well. It can be transmitted by:

  • Kissing
  • Touching the skin
  • Sharing things like lip balm, razors, or silverware

Once you are infected with HSV-1, the virus "lives" in your nerve cells permanently, causing periodic outbreaks of cold sores.

Common triggers of cold sores include:

  • Sun exposure
  • Stress
  • Fever

Oral Herpes vs Genital Herpes

Genital herpes is typically caused by a different strain of the herpes virus, called HSV-2. Rarely, the HSV-2 virus can spread from the genitals to the mouth during oral sex and cause oral herpes. The reverse is also true: In some cases, HSV-1 can spread from the mouth to the genitals, causing genital herpes.

How to Treat Cold Sores

There is no cure for HSV, but treatments are available. Sores and blisters typically clear up on their own, but treatment is often used to reduce the severity and duration of outbreaks.

Antiviral creams and ointments can help with itching, and oral antiviral medications, including Zovirax (acyclovir), Famvir (famciclovir), and Valtrex (valacyclovir) can shorten an outbreak. When oral medication is taken on a daily basis, it not only can help with outbreaks, but it also can prevent those who are infected from infecting others.

You can also ease the discomfort of symptoms by:

  • Applying ice or a warm washcloth to the sores to help ease pain
  • Avoiding hot beverages, citrus fruits, and spicy foods
  • Taking a pain reliever such as Tylenol (acetaminophen)

Complications and Risk Factors Associated With Cold Sores

In some cases, the herpes virus can spread to the eyes, causing ocular herpes, or herpes keratitis. Symptoms can include discharge or a “gritty” feeling. Without treatment, ocular herpes can cause scarring in the eye and affect vision.

In people who have a weakened immune system due to cancer or HIV infection, oral herpes can cause a systemic (widespread, whole-body) infection.

Are There Tests to Diagnose Cold Sores?

Healthcare providers can typically diagnose a case of herpes by looking at the sores. A swab may be taken and sent to a laboratory for confirmation. If no sores are present, a blood test can detect HSV.

When to See a Healthcare Provider

Most cold sores are not serious, however they can be uncomfortable. You should call your healthcare provider if:

  • Your symptoms are severe or don't go away after a couple of weeks
  • You have sores or blisters near your eyes
  • You have a weakened immune system


Cold sores are clusters of small, fluid-filled blisters that form on or around the mouth. They are caused by the herpes simplex virus (HSV-1) While there is no cure for HSV, there are treatments like antiviral creams and medications that you can take to help shorten the outbreak, address symptoms, and reduce the likelihood of infecting others. 

A Word From Verywell

Cold sores are very common. They can be uncomfortable and can make you feel self-conscious. Knowing what triggers your outbreaks can help you prevent cold sores from forming, and oral and topical anti-viral medications can shorten their course.

Frequently Asked Questions

  • What does a cold sore look like?

    Cold sores look like small, fluid-filled blisters. They can be in clusters or a single blister. While they usually are on the lips and around the mouth, they can be anywhere on the face. The blisters will break open and crust over before healing.

  • How long after a cold sore can you give oral sex?

    You should wait until the sore is healed completely and after the scab falls off before giving oral sex. Using condoms or a dental dam during oral sex can help reduce the likelihood of infection even more.

  • How does a cold sore start?

    Cold sores typically start out with redness, swelling, pain, tingling, or itching where the cold sore will appear. If this is your first outbreak, you may also have significant flu-like symptoms like swollen glands and a headache.

  • Can you prevent a cold sore?

    Avoiding skin-to-skin contact with others is one way to prevent it. If you are already infected, taking an antiviral medication can help to stop the virus from replicating and may help to prevent or reduce the risk of cold sores.

  • How can you hide a cold sore?

    You can hide a cold sore using concealer, but before you do, treat the area with your prescribed topical cream or a cold compress to help reduce swelling. The process is similar to covering up a pimple. Do not pop or pick at a cold sore or blister.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. American Academy of Dermatology Association. Herpes simplex: Signs and symptoms.

  3. Johns Hopkins Medicine. Oral herpes.

  4. American Academy of Dermatology Association. Herpes simplex: Who gets and causes.

  5. National Library of Medicine. Medline Plus. Herpes—oral.

  6. Centers for Disease Control and Prevention. STD facts—genital herpes.

  7. American Association of Dermatology Association. Herpes simplex: Diagnosis and treatment.

  8. American Academy of Ophthalmology. What is herpes keratitis?

  9. NHS. Cold sores.

  10. Planned Parenthood. I had oral sex with a girl who had a cold sore. Could I have herpes? 2011.