What is a cold sore?
A cold sore is a fluid-filled blister (or a cluster of blisters) that appears on the lips and around the mouth. Cold sores are also called fever blisters, oral herpes or herpes labialis.
Are cold sores contagious?
While cold sores are highly contagious, they usually aren’t serious. In healthy people, cold sores generally clear up on their own in one to two weeks.
How common are cold sores?
Cold sores are widespread. More than half of the people in the United States have been infected with the virus that causes cold sores, though many people never develop cold sores or have any symptoms. About 20 to 40 percent of people who have the virus develop cold sores.
How often do people get cold sores?
A cold sore can develop multiple times a year or only once or twice in your lifetime. The frequency of a cold sore outbreak varies from person to person.
Who is affected by cold sores?
People of all ages can become infected with the virus that causes cold sores. Many people are exposed to the virus during childhood.
It is possible to develop a cold sore at any age, though the chance of having a cold sore outbreak decreases after the age of 35.
Symptoms and Causes
What are the symptoms of cold sores?
For many people, symptoms are more severe the first time they develop a cold sore. When you have a cold sore outbreak:
- The first sign of a cold sore is usually a tingling, burning, or itching sensation on or around the lips, beginning about 12-24 hours before the cold sore develops.
- The area becomes red, swollen and painful as the blisters form.
- Over 2-3 days, the blisters rupture and ooze fluid that is clear or slightly yellow. This is sometimes called the “weeping phase.”
- About 4-5 days after the cold sore appears, it crusts and scabs over. It might crack or bleed as it heals.
- The scab then falls off, revealing skin that may be a little more pink or reddish than usual for a few days. It usually takes 1-2 weeks for the cold sore to heal completely.
What causes cold sores?
Cold sores are sometimes called oral herpes because they are caused by the herpes simplex virus type 1 (HSV-1). This virus is very common and highly contagious. It spreads through saliva or close contact — often through kissing or by sharing utensils, straws, towels or lip balm with someone who has a cold sore.
You may not know if you have been infected with HSV-1 because symptoms of exposure to HSV-1 are generally mild. Children sometimes develop a fever and small blisters inside and around their mouths when they are first exposed to HSV-1.
What triggers a cold sore?
After you have been infected with HSV-1, the virus never goes away. It remains dormant (inactive) in a group of nerve cells in your face called the trigeminal ganglion.
When the virus is triggered, or activated, it “wakes up” and travels through your nerves to your lips, where a cold sore develops. After an outbreak, the virus goes back to sleep in your body.
What triggers a cold sore in one person might not cause an outbreak in another person. Some people with HSV-1 never develop a cold sore.
A cold sore can be activated by a variety of factors, including:
Diagnosis and Tests
How is a cold sore diagnosed?
Your doctor will probably be able to tell if you have a cold sore by looking at the affected area. He or she may also swab the cold sore to test the fluid for the herpes simplex virus.
How do I know if I have a cold sore?
If you’ve had one before, you’ll likely recognize the symptoms: a tingling sensation followed by redness, swelling and blisters on or around your lips. You can visit your doctor for a diagnosis, although it is not always necessary to go to the doctor if you have a cold sore.
Management and Treatment
How do you get rid of a cold sore?
Although it may take a while to get rid of a cold sore, some medicines can shorten the healing time and make the symptoms less painful. Cold sore treatments include:
- Over-the-counter medications: You can buy without a prescription creams or ointments that you apply directly to the cold sore. If you start using these creams when you first notice tingling or itching — before the cold sore forms — you may be able to prevent the cold sore from appearing.
- Oral antiviral medicine: Your doctor may prescribe an antiviral medication that you take orally (by mouth).
- Intravenous (IV) antiviral medicine: If other medications aren’t working, your doctor may need to prescribe an antiviral medication that will be administered through an IV. In this case, your doctor will monitor you closely throughout treatment.
What are the complications associated with cold sores?
Although complications from cold sores are rare, they can include:
- Eye infections: The herpes simplex virus (HSV-1) can spread to the eye when someone touches a cold sore and then touches their eye. If HSV-1 spreads to the eye, it can cause HSV keratitis — a potentially serious infection of the cornea. Severe HSV keratitis infections can lead to blindness.
- Genital sores: HSV-1 can spread to the genitals through oral sex, producing warts or ulcers on the genitals or anus. But even though people sometimes call it oral herpes, HSV-1 is not the same as HSV-2, the sexually transmitted virus that causes most cases of genital herpes.
For certain groups of people, cold sores can lead to serious complications. The following groups of people should receive medical treatment immediately if they have a cold sore:
- Newborns: Babies under 6 months old may develop complications such as high fever and seizures because their immune systems aren’t fully developed.
- Immunocompromised people: For people with weakened immune systems, the herpes simplex virus can lead to encephalitis (swelling of the brain). If you have HIV or are undergoing chemotherapy, cold sores could be more severe and could take longer to go away.
- People who have eczema: The herpes simplex virus can cause a life-threatening infection called eczema herpeticum in adults and children with eczema. It is important to see your doctor right away if you have eczema and you develop a cold sore.
What can I do to help relieve symptoms of cold sores?
While cold sores are uncomfortable, you can find relief at home. Suggestions to help manage cold sores:
- Use over-the-counter creams and ointments: These remedies can help shorten the healing time and ease your symptoms. They are most effective when you use them as soon as you feel a cold sore coming on.
- Take pain relievers: If you are in a lot of pain, your doctor may recommend an over-the-counter topical pain reliever such as lidocaine that you can apply directly to the cold sore. You can also take acetaminophen or ibuprofen by mouth to ease your discomfort.
- Wear sunscreen and SPF lip balm: It is important to make sure a cold sore doesn’t get sunburned while it is healing. Also, wearing a lip balm with SPF 30 every day could prevent future cold sores.
- Avoid acidic foods: Orange juice, tomatoes and other acidic foods can aggravate a cold sore.
- Apply a cool compress: You can use a cool, damp washcloth to soothe a cold sore. Apply it for a few minutes off and on throughout the day. Be sure to wash the towel after you’ve used it to avoid spreading the cold sore to others.
How can you prevent cold sores?
To avoid being infected with HSV-1, you should take the following precautions around people who have cold sores:
- Avoid kissing, intimate contact and oral sex with someone who has a cold sore.
- Don’t share towels, razors, dishes, cutlery, straws, lip balm or lipstick.
- Wash your hands before touching your lips, eyes or genitals.
If you’ve already come into contact with HSV-1, do these to reduce risk of a cold sore outbreak:
- Try to stay healthy: A fever can trigger a cold sore, which is why people sometimes call them fever blisters.
- Get enough rest: Fatigue weakens your immune system and makes you more likely to get sick.
Wear lip balm with SPF: Protecting your lips from sunburn can help you avoid an outbreak.
If you have a cold sore, be careful around babies. Always wash your hands, and do not kiss a baby until the cold sore has healed completely.
Outlook / Prognosis
What is the outlook for patients who have cold sores?
The majority of people who develop cold sores learn to live with and manage their outbreaks. In healthy people, cold sores usually clear up in one to two weeks and have no lasting effects. However, in young babies, immunocompromised people and those with eczema, cold sores can cause life-threatening infections.
When should I call my doctor about my cold sores?
You should seek treatment for a cold sore if you have:
- Eczema (also known as atopic dermatitis)
- Numerous, frequent or extremely painful cold sores
- An outbreak that doesn’t clear up on its own in about 2 weeks
- Sores on your eyes, hands, genitals, or another part of your body
- HIV or cancer
- A compromised immune system, or if you are undergoing chemotherapy or taking medication that weakens your immune system
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy