What Are Cold Sores? Causes, Symptoms, and Treatments

Written by WebMD Editorial Contributor
Medically Reviewed by Zilpah Sheikh, MD on February 05, 2026
5 min read

A cold sore is a group of tiny, painful blisters caused by the herpes simplex virus (HSV). They're also called fever blisters or herpes simplex labialis.

Up to 90% of people around the world have at least one form of HSV.

Your symptoms are usually the most serious the first time you get cold sores. A first-time cold sore can make a child seriously ill.

After the first outbreak, your body should make antibodies, and you may never have another infection. But many people get cold sores that come back.

Cold sores are most likely to show up on the outside of your mouth, lips, and buttocks, but you can also get them on your nose and cheeks. You may get cold sores as late as 20 days after you're infected. The sore might appear near where the virus entered your body.

Cold sore symptoms include:

  • Fluid-filled blisters or red, painful, burning, or itching sores typically on or near your mouth, or on your fingers
  • Swollen, sensitive gums of a deep red color
  • Fever, flu-like symptoms, and swollen lymph nodes in the neck (often seen during the first attack; recurrent sores usually don't produce these symptoms)
  • Tingling and itching in the area of a prior outbreak

First-time infections may cause:

  • Burning and pain inside your mouth
  • Sore throat
  • Pain when you swallow
  • Headache
  • Upset stomach

Cold sores happen in stages:

  1. You have a tingling, burning, or itching feeling.
  2. About 12-24 hours later, blisters form. The area becomes red, swollen, and painful.
  3. The blisters break open, and fluid comes out. This usually lasts two or three days.
  4. A scab forms on the sore. It might crack or bleed.
  5. The scab falls off.

You catch HSV when you come into contact with people or things that carry the virus. For instance, you can get it from kissing someone who has the virus or from sharing eating utensils, towels, or razors.

Two types of the virus can cause cold sores: HSV-1 and HSV-2. Both types can also cause sores on your genitals and can be spread by oral sex. 

Type 1 usually causes cold sores, and type 2 mostly causes genital herpes, but either can be found in both areas.

Certain things can trigger an outbreak, including:

  • Some foods
  • Stress
  • Fever
  • Colds
  • Allergies
  • Fatigue
  • Sunburn or being in strong sunlight
  • Dental work or cosmetic surgery
  • Your period

Cold sores generally aren't serious, but the infection may be life-threatening if you have a weakened immune system because of AIDS, another condition, or medications.

If you have a serious case of the skin condition eczema, you may get cold sores over large parts of your body.

Your doctor might diagnose a cold sore just by looking at the blisters. They can also swab the blister and test the fluid for HSV.

There's no cure for cold sores. Once you have the virus, it stays in your body. The sores usually heal on their own in one or two weeks.

Antiviral medications can speed up healing, especially if you take them at the first sign of an outbreak. Your doctor might tell you to use:

  • Cream that you apply on the sores. Acyclovir (Zovirax) and penciclovir (Denavir) require a prescription, or you can get docosanol (Abreva) over the counter.
  • Pills you swallow, such as acyclovir (Sitavig, Zovirax), famciclovir (Famvir), or valacyclovir (valtrex). You need a prescription to get these.
  • Medicine injected into your bloodstream (via IV), such as foscarnet (Foscavir), if you have a serious case. Acyclovir can also be injected.

Some home remedies can help you feel better while you heal:

  • Cold, damp compresses
  • Over-the-counter pain medicines such as acetaminophen and ibuprofen
  • Cream painkillers with benzocaine or lidocaine
  • Treatments with alcohol to dry out the blisters
  • Lip balms and creams to keep moisture in

Complications from a cold sore are rare, but they can happen if the virus spreads to another part of your body, including your:

  • Fingers: Infection is called herpeticwhitlow.
  • Genitals: You might have warts or ulcers on your genitals or anus.
  • Other areas of the skin: If you have eczema and get a cold sore, see your doctor right away to avoid a serious condition called eczema herpeticum. This painful rash covers large areas of skin.
  • Eyes: HSV keratitis, an infection in your cornea, can cause blindness.
  • Brain or spinal cord: The virus can cause serious inflammation called meningitis or encephalitis, especially if you have a weakened immune system.

To lower your risk of another outbreak:

  • Get plenty of rest. A lack of sleep weakens your immune system, so you get sick more easily.
  • Wear lip balm with sunscreen. Look for SPF on the label.
  • Talk with your doctor. If you get sores often, they might have you take an antiviral medicine every day.

To keep from spreading the virus, when you have cold sores, don't:

  • Kiss anyone
  • Share eating utensils, glasses, towels, lipstick or lip balm, or razors
  • Have oral sex

Keep in mind that you can spread the virus even if you don't have symptoms.

A cold sore is a group of tiny, painful blisters caused by the herpes simplex virus (HSV). They're also called fever blisters or herpes simplex labialis. A lot of people — up to 90% of the world's population — have at least one form of HSV.

Cold sores are most likely to show up on the outside of your mouth, lips, and buttocks, but you can also get them on your nose and cheeks. Certain things can trigger an outbreak, including some foods, stress, and fatigue.

There's no cure for cold sores, but they usually heal on their own. Antiviral medications can speed up healing, especially if you take them at the first sign of an outbreak. Over-the-counter pain meds and cold, damp compresses can make you more comfortable in the meantime.

Why do glands swell when you have a fever blister?

Lymph nodes are sometimes referred to as glands, but they are not glands. If your lymph nodes swell when you have a fever blister, that's a sign that your body has detected an infection and is trying to fight it off.

How long do swollen lymph nodes last with cold sores?

Swollen lymph nodes typically occur when it's your first infection. You're unlikely to have swollen lymph nodes with future cold sores, but it's possible.