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A cold sore is a small blister or group of blisters that usually develop on the lip or around the mouth. Cold sores are caused by the herpes simplex virus (HSV).
Also known as fever blisters or herpes simplex labialis

If you get these, you’re not alone. More than half of Americans ages 14 to 49 carry the virus that causes them. The virus stays in the body after they clear. If the virus reactivates, or wakes up, you may get them again.

They are generally not serious. In healthy people, they tend to clear within two weeks.

They are so contagious that many people catch the virus that causes them by the time they’re 5 years old.

Cold sore on and above the lip

If you have one, you can spread the virus to others who don’t have the virus. Even when you treat them, you can still spread the virus to others. You are contagious until all the sores have scabbed over.

By taking the following precautions until all of the sores have scabs, you can avoid infecting others:

  • Don’t kiss people, especially children
  • Avoid other intimate contact
  • Avoid close contact with anyone who has a weakened immune system, including newborn babies
  • Don’t share personal items like lip balm, towels, or razors
  • Don’t share beverages or food
  • Try not to touch your cold sores
  • If you touch a cold sore or apply medicine to it, wash your hands immediately afterward
  • Wash your hands frequently throughout the day

These precautions are especially important if you are around a child who has eczema or someone who has a weakened immune system. If that person catches the virus, it can be very serious.


  • Just caught the virus (newly infected)
  • Have had the virus for some time

The following explains what signs and symptoms develop, and when.

Newly infected

Most people catch the virus when they are a child. Not every child who catches the virus, however, has symptoms. If symptoms occur, the child usually feels sick and has one or more of the following:

  • A burning sensation in the mouth, followed by painful mouth sores, which can form on the tongue, gums, lips, or throat
  • Sore throat
  • Pain when swallowing
  • Swollen lymph nodes (glands)
  • Fever
  • Aches and pains
  • Headache
  • Nausea

These symptoms last from one to two weeks.

It’s rare for adults to catch this virus. It’s so common and spreads so easily that most people get it in childhood.

If you catch the virus as an adult, you may or may not have signs and symptoms. If you do, you’ll have the same signs and symptoms as newly infected children. Adults often say they feel like they have the flu and have painful sores inside their mouth.

First cold sore outbreak in a young child's mouth

After you get infected, the virus travels to your nerves and stay there until it reawakens. Even if you never have symptoms, the virus will still travel to your nerves. Because there is currently no cure, the virus lives inside your body permanently.

Even with the virus inside your body, you may never get a breakout. Some people, however, get them occasionally, which tends to be less severe. The signs and symptoms also differ.

  1. Warnings symptoms begin. A day or two before an outbreak, you may feel one or more of the following where the breakout is going to appear:
  • Burning
  • Itching
  • Stinging
  • Tingling and the skin feels a little numb
  • Throbbing

Some people who have these warning symptoms never get a fully broken out cold sore.

Medicine, which you can buy without a prescription, can shorten how long they last. You need to apply it at the first sign of an outbreak.

  1. An outbreak appears. One or more painful, fluid-filled blisters appear. These usually form on your lips or around your mouth. They can also appear elsewhere on your face.If you have a sore near an eye, you should see an eye doctor immediately. The virus can spread to the eyes. Warning signs that this has happened include your eyes becoming sensitive to light or feeling painful. Your eyes may also feel gritty or runny.If any of these symptoms develop, you need immediate medical treatment. Without treatment, your eyesight could be affected. Sometimes, blisters appear elsewhere. They can appear on a hand or in the genital area. This can happen when you spread the virus from your mouth to other areas by touching a sore and then touching another part of your body. You can avoid spreading the virus to other parts of your body by not touching the sores. Washing your hands after touching a sore accidentally can also help prevent spreading the virus to other parts of your body.
  2. Sores crust over. Within 48 hours of the warning symptoms, sores usually break open. They will ooze fluid and then crust over (form scabs).In healthy people, most sores will disappear then within 5 to 15 days. They often heal without leaving a scar.

If you have cold sores for longer than 15 days, you should see your primary care doctor or dermatologist. Some people need treatment to get rid of cold sores.

Very Contagious

The virus that causes cold sores is very contagious, so many people get cold sores.

In the United States, people usually get this virus when they are a child. Getting kissed by someone who has a cold sore is often how a child catches the virus.

A child can also get the virus by eating from the same fork or spoon as someone who has a cold sore or sharing a towel with a person who has a cold sore.

Adults also catch the virus. That’s why it’s so important for everyone who has a cold sore not to kiss people or have intimate contact until the cold sore forms a scab. To prevent infecting others, it’s also important to stop sharing personal items like towels and razors until the cold sores form scabs.


Some people have triggers that cause outbreaks of cold sore. A serious sunburn triggered this teen’s cold sores.

Cold sore outbreak triggered by this teenager's serious sunburn

A virus causes cold sores. Most cold sores are caused by the herpes simplex virus (HSV). More than half of Americans ages 14 to 49 carry this virus.

Once you get the virus that causes cold sores, you have it for life. After the sores clear, the virus travels to your nerves, where it stays unless it reawakens.

After getting infected, some people never get a cold sore. Others see some cold sores, but then develop antibodies to the virus and never get another cold sore. It’s also possible to get cold sores throughout your life.

Outbreaks tend to occur less often after 35 years of age.

If you get cold sores, it’s likely that something triggers the virus to wake up. The following can be a trigger:

  • Stress
  • Fatigue
  • Illness, such as a cold, fever, or flu
  • Injury, such as a cut, to the area where you have had cold sores
  • Dental work
  • Cosmetic surgery or laser treatment
  • Strong sunlight
  • Certain foods
  • Hormonal changes, such as getting your period

What triggers cold sores in one person may not trigger them in another person.

How do dermatologists diagnose cold sores?

A dermatologist can often diagnose a cold sore by looking at it.

Your dermatologist may also swab a cold sore. Fluid from the sore can be examined to find out if you have a herpes virus called the herpes simplex virus (HSV). This is the virus that causes cold sores.

How do dermatologists treat cold sores?

To treat cold sores, a dermatologist may prescribe:

Antiviral medication: Cold sores are caused by a virus, so antiviral medications are used to treat them. Your dermatologist may prescribe medication that you:

  • Apply directly to the sores, such as docosanol cream or acyclovir cream
  • Take by mouth, such as acyclovir, valacyclovir, or famciclovir

For someone who has a serious outbreak and cannot get relief from the above, a dermatologist may prescribe an antiviral medication that you receive through an IV, such as foscarnet or cidofovir. You’ll be closely watched if one of these medications is necessary.

If you get cold sores often and have a weak immune system, your dermatologist may prescribe a prescription cream called penciclovir. It can reduce the time that you have an outbreak. To work, you need to apply it to the skin with the first symptoms, such as burning or tingling.


When applying medicine, dermatologists recommend gently dabbing the medicine on with a clean cotton-tipped swab.Young man with cold sore on lip

Pain medication: If you have a lot of pain, your dermatologist may prescribe a medication that you apply to the sores, such as lidocaine.

Sunscreen: While the sores are healing, it’s important to protect them from the sun. A lip balm with an SPF of 30 or higher and broad-spectrum protection can help protect your lips. Worn year round, this lip balm may help prevent new outbreaks.

Treatment can shorten your outbreak. It may even prevent you from getting a cold sore if you start treatment at the first sign of one (a tingling or burning sensation on your skin).

Treatment can also reduce your risk of spreading the virus to others. Treatment is highly recommended if you get a cold sore and have:

  • Atopic dermatitis (usually begins in childhood and is often called eczema)
  • Sores near your eyes
  • A lot of cold sores
  • A lot of pain
  • Sores that spread to another part of your body, such as your hands or genitals
  • HIV, AIDS, cancer, or another disease that weakens your immune system
  • Cancer and are getting chemotherapy
  • To take medication that suppresses your immune system, such as medicine to control severe psoriasis or prevent organ rejection
  • Outbreaks frequently
  • An outbreak that lasts more than two weeks

It’s important to treat cold sores if you have any of the above because they may not go away without treatment. Left untreated, the virus  can spread to other parts of your body. Some people develop another illness and become very sick.

If you’re healthy, you can treat them on your own. Find out what dermatologists recommend at, Cold sores: Self-care.


Cold sores cannot be cured. Some people get the virus and have just one outbreak. Others continue to get outbreaks over their lifespan.

If you get cold sores several times a year, tell your dermatologist. A prescription antiviral medicine may help. Taking this medicine at the start of an outbreak can shorten the duration. Some people who get cold sores frequently take this medicine every day. Taken daily, it can help prevent outbreaks.


When to see a dermatologist

Some people need help to clear cold sores. You should make an appointment to see a dermatologist if you have:

  • Atopic dermatitis
  • A weakened immune system because you take a medicine that suppresses your immune system or have a disease that weakens your immune system
  • Close to your eyes
  • Happen several times a year
  • Lasting longer than 15 days

Treatment can help you feel better and prevent complications.

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