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Cold sores: Overview

Created: ; Next update: 2021.


Many people will be familiar with that typical tingling or itching feeling around their lips that comes about one day before cold sore blisters and swelling appear. Although these typical symptoms are bothersome, they usually go away on their own within one to two weeks.

They are caused by a certain type of contagious herpes virus. Many people have these viruses in their body, but they don’t always lead to cold sores. Those who have had a cold sore in the past will often keep on getting them, though.


Cold sores (herpes labialis) lead to the formation of painful blisters, typically only on one side of the lips. But the blisters can also spread to the surrounding skin or into the mouth.

Illustration: Cold sores, from left to right: Redness, blisters, crusting – as described in the article

Cold sores, from left to right: Redness, blisters, crusting

The blisters easily break open when you talk, laugh or chew. They then ooze fluid. Acidic foods and drinks like juice or vinegar can irritate the wound. When the wound heals, it crusts over into a scab.

Cold sores are often more unpleasant the first time you get them because your body doesn’t yet have any antibodies against the virus. They may then cause symptoms such as a fever, weakness and swollen lymph nodes in the neck area.

Young children also sometimes get a fever the first time they have a cold sore. The lining of their mouth may become severely inflamed and hurt, too. This leads to bad breath.


Cold sores are caused by herpes simplex viruses. There are two types of herpes simplex viruses, known as type 1 and type 2. Cold sores are usually caused by herpes simplex type 1, but can also be caused by herpes simplex type 2. The herpes virus is spread through the fluid in the blisters or open sores, for instance through kissing, oral sex, or shared objects.

The viruses live in a cluster of nerve cells (ganglion) at the side of the face, known as the trigeminal ganglion. People get a cold sore if the viruses move along the nerves to the lips, where they cause the typical symptoms. If you become infected with herpes viruses, they stay in your trigeminal ganglion for the rest of your life.

Cold sores mainly occur if the immune system is weak – for instance, due to a common cold or after strenuous physical activity. But it still isn’t clear why some people keep getting cold sores and others don’t.


It is estimated that about 60 to 90% of all people in Germany are carriers of the herpes simplex virus type 1. The likelihood of having the virus in your body increases with age. A lot of people aren’t aware that they have it because they don’t have any symptoms. It is thought that the virus ends up leading to cold sores in about 20 to 40% of people who have it.


Many people can already feel their lip tingling or itching several hours or a day before visible blisters form. While the sores are healing, they may crust over into scabs, which can also easily crack and bleed.

It takes about one to two weeks for cold sores to go away. The small wounds don’t leave any visible scars.

Some people keep on getting cold sores – usually one to two times per year. But about 5 to 10% of people who get them have more than five per year. The symptoms often become less severe over time, though.


In people who are otherwise healthy, cold sores go away on their own without any long-term health consequences.

If someone has a skin condition like eczema or severe burns, the herpes virus can infect larger areas of skin. This rarely happens, though.

In people who have a very weak immune system, the infection can take longer to go away, be more severe and sometimes lead to complications. Things that weaken the immune system include immune disorders like HIV and chemotherapy for the treatment of cancer. Some medications that are used following a bone marrow transplant or organ transplant make the immune system more susceptible too.


Cold sores can be easily diagnosed based on the typical symptoms. Most people who have had a cold sore in the past know that they’re getting another cold sore as soon as they notice the first signs. It usually isn’t necessary to go to a doctor.

In rare cases, the herpes infection occurs in skin elsewhere on the body. The doctor can then take a sample of fluid from the blisters and have it tested for herpes viruses in a laboratory.


Certain things can activate the herpes virus. These include

  • UV rays (from natural sunlight or a tanning bed),
  • very hot or cold temperatures,
  • damaged or cracked lips, and
  • physical or emotional stress.

Avoiding these things may lower the risk of getting a cold sore. Sunscreen and good lip care might help too.

People who get cold sores very frequently are sometimes advised to take medication to try to prevent them. But there is hardly any research on how effective this medication is.

Until the cold sore blisters and scabs have completely gone away, you can protect yourself and other people from infection by

  • not kissing anyone,
  • not sharing towels, dishes and cutlery,
  • washing your hands if you touch your lips with them (for example, after putting on cream),
  • avoiding sports that involve physical contact, and
  • avoiding oral sex. The herpes virus can spread from the lips to the membranes lining the genitals, leading to genital herpes.

Newborn babies under the age of 8 weeks are particularly at risk because their immune system hasn’t had time to develop. Parents who have a cold sore should take care not to kiss the baby or put the baby’s pacifier in their own mouth. They should also wash their hands regularly and make sure that the baby doesn't accidentally touch their cold sore.

People who have cold sores don’t have to stay home from work or school.

Sometimes people pass the cold sore virus on to others even if they don’t have a cold sore at the time. This very rarely happens, though, so there’s no need to take any precautions if you don't currently have a cold sore.


Cold sores clear up on their own, so there’s usually no need for treatment.

Antiviral ointments, creams, patches or gels can speed up the healing process by about one day. Sometimes they can prevent blisters and scabs from forming too. They contain the drugs aciclovir or penciclovir, and are available from pharmacies without a prescription.

It’s important to use them correctly: In order for the treatment to be able to work, it has to be started within 24 hours of the first symptoms arising. The sooner you start it, the better. The antiviral medications are then applied to the affected area every 2 to 3 hours, over a period of five days.

Unlike creams and other topical (external) treatments, antiviral tablets are only available on prescription. These tablets can also speed up the healing process by about one day. It’s not clear whether they are more effective than topical treatments. But they are easier to use because you only need to take them once or twice a day.

The protective effect of tablets is much greater in people who have a weak immune system, for instance during chemotherapy.

Further information

When people are ill or need medical advice, they usually go to see their family doctor first. Read about how to find the right doctor, how to prepare for the appointment and what to remember.


© IQWiG (Institute for Quality and Efficiency in Health Care)
Bookshelf ID: NBK525782


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