What Are Cold Sores?

woman with cold sore on lip

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Cold sores—also called fever blisters—are painful, fluid-filled sores that most commonly appear on the cheeks, lips, and tongue. An infection of the herpes simplex virus type 1 (HSV-1) typically causes cold sores to occur. An estimated 3.7 billion people in the world have HSV-1 in their bodies and about 90% of adults are infected with the virus, but many do not show symptoms.

While proper treatment can shorten the duration of cold sores, they don't cure the virus that causes them. That's why some people may have frequent cold sore flare-ups. Fortunately, there are treatment options that can reduce painful symptoms until the flare-up subsides.


Cold sores can differ based on which part of your body they appear on. You can develop a cold sore on one or more of the following parts:

  • Mouth
  • Eyes
  • Fingers
  • Genitals


The initial cold sore symptom is a burning sensation on your skin that indicates the sore may be forming. When the cold sore (or sores) do form, you may experience the following symptoms:

  • Fluid-filled blisters that commonly form on or around the lips
  • Tingling sensation around where the blister is
  • Fatigue
  • Swollen lymph nodes
  • Mild fever

Children may experience slightly different cold sore symptoms compared to adults, such as having a poor appetite and drooling during the day.


The most common cause of cold sores is herpes simplex virus type 1 (HSV-1). When you get an HSV-1 infection, you may typically experience irritation on the skin and around your mouth. As the infection spreads, the virus penetrates the skin and rests in your nervous system cells called neurons. The virus continues to live in the neurons, potentially causing later symptoms, such as pain and tingling, before another herpes flare occurs.

When you have HSV-1, the virus can go into latency—or a period where you don't experience any symptoms. However, stress to the body can potentially cause a flare-up to occur and make new or worsening cold sores. Examples of stressful situations that can influence a flare-up include:


A healthcare provider can often diagnose a cold sore by physically examining it. However, if your provider is not exactly sure what the sore is, they may take a swab of the sore to obtain some fluid from it. They can send the fluid sample in for laboratory testing to confirm the presence of HSV-1 or other possible infections.

Cold sores can appear very similar to canker sores, but canker sores usually only occur on the inside of the mouth while cold sores usually appear on the outside of the mouth. Canker sores are also not as contagious as cold sores.


Cold sore treatments can help reduce flare-ups and the appearance of cold sores. But it's important to note that treatment cannot cure HSV-1. For this reason, you can have cold sores again in the future even after using treatments.

Antiviral medications are the most common cold sore treatments. These medications help keep the virus from multiplying, which can help reduce the number of cold sores you develop. Antiviral treatment can also reduce how long the cold sores stay on your body and can help heal the sores quicker.

You can try antiviral medication in a variety of forms, including:

  • Topical: Using creams such as Zovirax (acyclovir) that you can apply with a cotton swab
  • Oral: Taking pills such as Valtrex (valacyclovir) and Famvir (famciclovir)
  • Intravenous (IV) injections: Getting antiviral treatments administered by a healthcare provider including Vistide (cidofovir)

You don't always have to apply or take prescription antiviral treatments for all cold sores. However, treatment can reduce the length of your symptoms and prevent you from spreading the virus to other people. Additional treatments for cold scores include:

  • Topical pain relievers: Applying lidocaine-containing creams may help reduce the pain
  • Over-the-counter pain relievers: Taking medications such as ibuprofen may help reduce some of the pain associated with cold sores
  • Cold temperatures: Eating popsicles or ice chips can be soothing to the blistered areas and help you feel more comfortable

If you do have cold sores several times a year, talk to your healthcare provider about getting an antiviral prescription to reduce the duration of your next flare-up.


People transmit HSV-1 through close contact with each other. If you have a cold sore outbreak, anything that touches your lips and mouth could potentially transmit to another person. For this reason, you should avoid:

  • Kissing
  • Engaging in oral sex
  • Sharing cups, utensils, water bottles, lipstick, or razors

In addition to preventing cold sore transmission, you can also avoid a cold sore flare-up by avoiding sun exposure. Wearing lip sunscreen with a sun protection factor (SPF) of at least 30 can help.

Related Conditions

Sometimes, other underlying medical conditions can worsen your cold sore symptoms. These conditions include:

  • Atopic dermatitis (eczema)
  • Autoimmune disorders such as HIV/AIDS
  • Cancer

If you live with one of the above conditions, it's a good idea to talk to your provider about antiviral medications that can help you reduce cold sore flare-ups. That's important because these conditions can affect your immune system's ability to fight off the cold sore infection. Your cold sores probably won't go away without prescription treatments and you may be at a higher risk of developing other infections because your body is trying to fight too many harmful cells.

Living With Cold Sores

Cold sores can be painful to experience. They are also highly visible, which can make it difficult to hide their appearance when you are having a flare-up. The good news is that antiviral medications can help reduce your flare-ups and the duration of your cold sores. If you have HSV-1 or are experiencing cold sores, your healthcare provider can help you figure out the treatment and prevention options that are right for you.

Frequently Asked Questions

  • Does a cold sore mean I am sick?

    Cold sores can cause symptoms of other illnesses (such as a cold or flu), including fever and fatigue. However, most people are not seriously ill when they have a cold sore.

  • Is it OK to kiss someone with a cold sore?

    Cold sores are highly contagious. To prevent spreading the HSV-1 infection, you shouldn't kiss someone with a cold sore.

  • How long is a cold sore contagious?

    Cold sores are contagious until they are completely healed. That's why it's important to refrain from skin-to-skin contact or sharing items until a cold sore has gone away.

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5 Sources
Health.com 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.
  1. Zhu S, Viejo-Borbolla A. Pathogenesis and virulence of herpes simplex virus. Virulence. 2021;12:2670-2702. doi: 10.1080/21505594.2021.1982373

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

  3. American Academy of Dermatology Association. Cold sores: diagnosis and treatment.

  4. National Institute of Dental and Craniofacial Research. Fever blisters & canker sores.

  5. World Health Organization. Herpes simplex virus.

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