Cold Sores Causes, Remedies, Diagnosis

A woman touches her lip.

What You Should Know

Cold sores, also known as fever blisters, can make you feel uncomfortable and self-conscious. What's worse, it seems like some people get them while others are apparently spared. Even though there is no cure, treatments are available to shorten the duration of the symptoms or bring some relief. This guide will show you how to recognize and manage cold sores.

Close up photo of herpes cold sore blisters

Colds Aren’t to Blame

Cold sores, despite the name, are not caused by the common cold. They are caused by a virus, specifically, the herpes simplex virus (HSV). Cold sores are contagious and are passed to others through direct contact or contact with body fluid. There are two different types of HSV- type 1 and type 2. Type 1 HSV usually caused cold sores. As the virus reproduces, it damages the skin and leads to blister formation that lasts about a week. In between outbreaks of cold sores, the virus remains present in the body inside nerve cells.

A woman gives another a social kiss.

Who Can Get Cold Sores and Why

Kissing is a common form of transmission of HSV, and estimates suggest that about half the population has been infected with HSV-1. But not everyone who has been infected will develop cold sores. Genetics may play a role in determining who does or doesn't get cold sores; a study in 2008 identified six genes that may increase a person's risk of getting cold sores.

Photo of a man driving.

Stress Can Be a Trigger

As mentioned, HSV remains in nerve cells in an inactive state for most of the time. Outbreaks occur when the infection becomes active again. Common triggers for outbreaks include stress, fever, sunlight, and menstruation. Outbreaks can occur as often as monthly in some people, while others are affected less commonly.

Photo of herpes blisters on the lip with an inset of a canker sore on the inner lip

Canker Sores Are Different

Sometimes cold sores are confused with canker sores. Canker sores affect the inside of the mouth and are not caused by the herpes virus. In contrast to canker sores, cold sores usually develop on the lip and not inside the mouth. The cause of canker sores is poorly understood, and canker sores are not contagious like cold sores.

Photo of oozing cold sore.

When You're Contagious

HSV is contagious from the time the skin turns itchy or red until the sores heal. Sometimes, the virus can even be spread through the saliva of an infected person, even if that person does not get cold sores. The most contagious period is the time when blisters are present and just after the blisters have ruptured.

A couple about to kiss

How Does the Virus Spread?

HSV spreads through contact with sores or body fluids. Even without obvious sores, the virus is usually present on the lips of an infected person. So kissing remains a major way that the virus is transmitted to other people. HSV-1 is also found in saliva, so sharing drinking glasses or eating utensils can spread the infection. Genital infection with HSV-1 can occur after oral sex.

A woman feeds a man with a fork.

How to Avoid Spreading Cold Sores

Although it may not be completely possible to eliminate the chance of getting cold sores, using caution when sores are present can reduce the possibility of spreading the virus. This means no kissing, no oral sex, and no sharing of toothbrushes, eating utensils, or drinking glasses.

A woman with her hand on her mouth in pain.

Relieving Cold Sore Pain

The initial outbreak of cold sores is usually most severe and can last up to two weeks. Recurrent outbreaks typically last about a week. Some over-the-counter creams or gels can offer pain relief, and some people find hot or cold compresses to be helpful in relief of burning and pain.

A woman applies herpes medication to her lip.

Antiviral Creams

Antiviral creams may reduce healing time, but these must be applied at the very first sign of an outbreak. Docosanol cream (Abreva) is available over the counter. Prescription creams include acyclovir (Zovirax) and penciclovir (Denavir).

A pharmacist holds a bottle of prescription pills.

Prescription Cold Sore Medications

Oral antiviral drugs can also speed healing time, but like their topical counterparts, they must be taken at the very first sign of an outbreak. Acyclovir (Zovirax) is taken at the first sign of the cold sore, then orally five times daily. Valacyclovir (Valtrex) is taken immediately at the first sign of a cold sore and then 12 hours later. Famciclovir (Famvir) is given as a single dose.

A photo of a herpes sore under the nose and above the lip

Is This a Cold Sore?

Cold sores don't always appear on the lips. They can develop in other areas of the face, including the cheek, nose, or chin. Recurrent outbreaks tend to occur at the same location each time.

A woman crosses her arms and legs.

Can You Spread It Around Your Body?

Spread of a cold sore to another part of your body is not common, but it is possible. It can happen by touching a cold sore and then touching an area of broken skin or a mucus membrane (moist lining tissue, as is found in the eyes or vagina). You can prevent this self-spread (known as autoinoculation) by careful hand washing and not touching the cold sore.

A photo of a herpes eye infection

Herpes Eye Infections

HSV can infect the eye (ocular herpes) or the finger (herpetic whitlow). Ocular herpes usually involves the cornea and can cause eye damage, including blindness if not treated promptly. Herpetic whitlow usually occurs because of finger or thumb sucking in children with cold sores, or when adults touch the lips or mouth of someone who has cold sores without wearing gloves.

Photo of a yoga class.

Outbreak Prevention

Limiting your exposure to triggers can help reduce cold-sore outbreaks. Use sunscreen and UV-blocking lip protection to avoid sun exposure. Relaxation and stress-management techniques can help reduce stress. Getting plenty of sleep and exercise can ensure your immune system is as healthy as possible.

A woman with two cold sores on her top lip

When to Visit a Doctor

If you have frequent or severe outbreaks of cold sores, discuss the condition with your doctor. He or she can recommend medications to reduce the severity of the symptoms and speed the healing process.



  1. Stockbyte
  2. © Interactive Medical Media LLC. All rights reserved.
  3. John Rowley / Stone
  4. Bernd Opitz / Riser
  5. © Interactive Medical Media LLC. All rights reserved.
  6. © Interactive Medical Media LLC. All rights reserved.
  7. Cormac Hanley / The Image Bank
  8. Peter Scholey / Photographer's Choice
  9. Studio MPM / Photonica
  10. © BSIP / Phototake -- All rights reserved.
  11. Jupiter Images Unlimited
  12. © Interactive Medical Media LLC. All rights reserved.
  13. Advertisement
  14. Alain Daussin / Riser
  15. © ISM / Phototake -- All rights reserved.
  16. Thomas Northcut / Riser


  • Medscape: "Herpes Simplex"
WebMD does not provide medical advice, diagnosis or treatment. See additional information