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Cold sores (oral herpes)

Oral herpes is a very common mouth infection caused by the Herpes simplex virus (HSV). It causes small, fluid-filled blisters to develop around the lips or inside the mouth. These are commonly known as cold sores.

  • About oral herpes
  • Symptoms
  • Causes
  • Diagnosis
  • Treatment
  • Special considerations
  • Prevention
  • Further information
  • Sources
  • Related topics

About oral herpes

Oral herpes is caused by the Herpes simplex virus (HSV). You can get oral herpes through skin-to-skin contact with someone who has the herpes virus or by sharing objects which have been in contact with the virus such as a razor or a lipstick.

From the first time you get a HSV infection (primary infection), the virus remains in your body for the rest of your life but is inactive (dormant). However, from time to time the virus can become active again and cause cold sores to develop.


Many people don't get any symptoms the first time they get oral herpes (primary infection) and the infection goes unnoticed. However for some people, the primary infection can cause symptoms and make them feel unwell. Children under the age of five are most likely to be ill from a primary infection.

Symptoms of a primary oral herpes infection can include:

  • blisters on the border between the lip and the surrounding skin (which may crust over)
  • blisters inside the mouth (stomatitis)
  • swollen and painful gums (gingivitis)
  • sore throat and swollen glands
  • bad breath (halitosis)
  • feeling generally unwell with flu-like symptoms such as a fever and headache
  • an increased amount of saliva in your mouth
  • dehydration

Children more commonly get blisters in and around the mouth and swollen painful gums. The mouth sores can last for 10 to 14 days, during which time eating and drinking can be difficult.

If you get symptoms from a primary infection during adulthood, you are more likely to have a sore throat and swollen tonsils or a glandular-fever type illness (see Related topics).

After you have the primary infection, whether or not you have symptoms, the virus lies dormant in your body but can become active from time to time. Recurrent episodes of the infection are commonly known as "cold sores". These usually occur on the border between the lip and the skin surrounding the skin.

Symptoms of a cold sore can include:

  • a tingling sensation, redness and swelling around the lip before the cold sore develops
  • small, fluid-filled blisters which break open and develop a yellow crust (scab). The scab usually falls off around seven days later

Recurrent cold sores tend to appear in or around the same place each time.


HSV can spread to other areas of skin around the body such as the fingers, eyes or genitals (see Related topics).

A HSV infection can be severe, and sometimes fatal, particularly if you have a weakened immune system (see Special considerations). On very rare occasions individuals with atopic eczema may also get a severe infection.

Rarely, HSV can be passed on to your baby during birth (see Special considerations).


Oral herpes is caused by HSV. There are two types of this virus, HSV-1 and HSV-2.

Oral herpes is usually caused by HSV-1 but HSV-2 can sometimes be the cause. Both types of HSV can also cause genital herpes (see Related topics).

You can get oral herpes through skin-to-skin contact with someone who has the herpes virus or by sharing objects which have been in contact with the virus such as a razor or a lipstick. The herpes virus can also be passed between the mouth and the genitals during oral sex.

There are a number of things that can trigger an episode of cold sores. These include:

  • emotional stress
  • tiredness
  • menstruation
  • strong sunlight on the lips
  • an injury to the mouth or a dental procedure
  • a fever

For many people, however, the trigger is unknown.


You may wish to go and see your GP if you have oral herpes. Usually, your doctor will be able to recognise oral herpes from looking inside and around your mouth. However, he or she may also take a swab of fluid from the blister or sore. The sample will be sent to a laboratory to confirm that you have the herpes virus.


There is no treatment that can get rid of the herpes virus from your body. Once you are infected it will remain in your body, even if you never get another episode. An episode of oral herpes will clear up on its own, usually within a week or so.

Treatment for cold sores

There are steps that you can take to help relieve any pain or discomfort from cold sores and prevent them spreading:

Take an over-the counter painkiller, such as paracetamol or ibruprofen to ease any pain or discomfort if necessary.

Anti-viral cold sore creams (which you can get over-the-counter from your pharmacy) can help the cold sore to clear more quickly, particularly if applied when you first notice symptoms, such as a tingling sensation around your lips, before the blister appears. Don't share cold sore creams with anyone else.

Occasionally, if the infection is particularly severe or frequent, your GP may prescribe anti-viral tablets

Creams and liquids (which you can get over-the-counter from your pharmacy) can ease irritation once the cold sore has developed. These should be dabbed on, and not rubbed in, to prevent further irritating the skin.

Try not to touch the cold sore and if you do, wash your hands thoroughly to prevent spreading the infection.

Don't kiss or have oral sex until you (or your partner's) cold sores have completely healed.

Don't share any objects which have been in contact with the virus such as a lipstick or lip gloss, razor, face towel or cutlery.

Wash your hands thoroughly before putting your contact lenses in to prevent HSV infection in the eye.

Always follow the instructions in the patient information leaflet that comes with the medicine and ask your pharmacist for advice on if it's suitable for your individual circumstances.

Treatment for blistering of the mouth and gums

If you or your child has severe blistering of the mouth and gums, there are other treatments that may be needed. Your doctor may give you a cream to help relieve pain and may also give you a mouthwash to help maintain good oral hygiene if brushing your teeth is painful.

The self-help steps for cold-sores can help if you or your child has this problem, but in addition to these you should also:

  • drink plenty of water to avoid dehydration; it's particularly important to check that your child is drinking enough as they may avoid drinking because of a painful mouth
  • eat cool, soft foods and avoid foods which are salty or acidic
  • use a lip barrier cream (such as Vaseline) to stop your lips sticking together

Special considerations

If you have a weakened immune system

If you have a weakened immune system (for example HIV/AIDS or certain types of cancer treatment), you should visit your GP if you develop either primary or recurrent oral herpes because the infection can be severe and you may develop complications.

If you are pregnant

Although very rare in the UK, HSV can occasionally be passed on to your baby when he or she is born. This is known as neonatal herpes and can cause your baby to be seriously ill. If you have oral herpes when you are pregnant, particularly in the later stages of pregnancy, you should go and see your GP or obstetrician for advice.

You shouldn't kiss anyone or share anything which may have come into contact with HSV (such as cutlery or lipstick) when you are pregnant.

If you have eczema

If you have eczema and HSV together, this can cause a severe rash called eczema herpeticum. You should see your GP for advice about this.


There are ways that you can lower your risk of getting or passing on oral herpes and prevent recurrent episodes.

  • use sun block on your lips if overexposure to sunlight triggers your cold sores to develop
  • don't kiss someone who has a cold sore
  • don't have oral sex if you or your partner has a cold sore or has genital herpes
  • don't share any creams, medicines, make-up or any object which may have come into contact with an infected area

Further information

Herpes Viruses Association


  • Herpes simplex - oral. NHS library for health. Clinical Knowledge Summaries 2007. www.cks.library.nhs.uk
  • Kumar P, Clark M, Clinical medicine. 6th ed. London: Elsevier Saunders, 2005
  • Beers M et al (eds) The Merck manual of medical information. 2nd ed. New York: Pocket books, 2004
  • Chantel S, Everitt H, Kendrick T. Oxford Handbook of General Practice. 2nd ed. Oxford: Oxford University Press, 2005
  • Herpes labialis (oral Herpes simplex). Medline plus. www.nlm.nih.gov/medlineplus, accessed 17 January 2008

Related topics

  • Genital herpes
  • HIV and AIDS
  • Glandular fever