Cold sore (herpes simplex virus)

Cold sores are small blisters that develop on the lips or around the mouth. They're caused by the herpes simplex virus. Cold sores usually clear up without treatment within 10 to 14 days.

About cold sores

Cold sores that keep coming back (recurrent) are shorter and less severe than a first infection.

Most people with recurrent herpes lip infections have two or more outbreaks (episodes) per year.

 A minority of people can have six or more outbreaks per year. Infections in the mouth can be more severe and last two to three weeks. 

Symptoms of cold sores

You may not have any symptoms when you first become infected with the virus (the primary infection). An outbreak of cold sores may occur some time later and keep coming back (recurrent infection).

If the primary infection does cause symptoms, they can be quite severe.

Herpes simplex virus primary infection

In children

Symptoms of the primary infection are most likely to develop in children younger than five years old. Symptoms include:

  • swollen and irritated gums with small, painful sores in and around the mouth – this is known as herpes simplex gingivostomatitis
  • sore throat and swollen glands
  • producing more saliva than normal
  • high temperature (fever) of 38C (100.4F) or above
  • dehydration
  • feeling sick (nausea)
  • headaches 

Herpes simplex gingivostomatitis usually affects young children, but adults can also develop it. It can last 10 to 14 days, with the sores taking up to three weeks to heal. Gingivostomatitis doesn't usually recur after the primary infection.

In adults

Primary herpes simplex viruses are rare in adults. But the symptoms are similar to those experienced by children.

Symptoms include:

  • you'll usually have a sore throat with or without swollen glands
  • you may also have bad breath (halitosis) and painful sores in and around your mouth - these can develop into ulcers with grey or yellow centres

If you develop the herpes simplex virus at an early age, it may be triggered from time to time in later life. It can cause recurring bouts of cold sores. 

Picture of a cold sore on a lip

After the primary infection, the symptoms are usually reduced to just the cold sores themselves.


Recurrent infections (cold sores)

Recurrent infections:

  • usually last for less time and are less severe than the primary infection
  • the only symptom is an outbreak of cold sores, although you may also have swollen glands
  • an outbreak of cold sores usually starts with a tingling, itching or burning sensation around your mouth
  • small fluid-filled sores then develop, usually on the edges of your lower lip
  • if you have frequent recurrent infections, you may develop cold sores in the same place every time - they may grow in size and cause irritation and pain
  • to start with they may ooze before crusting or scabbing over within 48 hours of the initial tingling sensation

Most cold sores, in a recurrent infection, disappear within 7 to 10 days without treatment and usually heal without scarring.

When to visit your GP

You only need to visit your GP if:

  • you're unsure whether it's a cold sore
  • it's severe and spreading further than just the lip
  • a cold sore hasn't healed after 10 to 14 days for a first episode, or seven to 10 days for a recurrence

Treating cold sores

Recurrent cold sores usually clear up by themselves without treatment within 7 to 10 days.

Antiviral creams and other treatments are available over the counter from pharmacies without a prescription.

If used correctly, these can help ease your symptoms and speed up the healing time.

To be effective, these treatments should be applied as soon as the first signs of a cold sore appear. This is when you feel a tingling, itching or burning sensation around your mouth. Using an antiviral treatment after this initial period is unlikely to have much of an effect.

Ask your pharmacist if you need information about treatments for cold sores.

If your GP thinks it is necessary, antiviral tablets may be prescribed for severe cases.

Complications of cold sores

Cold sores are usually mild, but may cause complications in rare cases. People with weak immune systems caused by illness or treatments such as chemotherapy are particularly at risk of complications.

If the infection affects the mouth or throat, dehydration sometimes occurs if drinking fluids becomes painful. Young children are particularly at risk of becoming dehydrated.

Preventing infection

The herpes simplex virus – or "cold sore virus" – is highly contagious. It can be easily passed from person to person by close direct contact.

After someone has contracted the virus, it remains inactive (dormant) most of the time.

It's not possible to prevent infection with the virus or prevent outbreaks of cold sores. But you can take steps to minimise the spread of infection.

Cold sores are at their most contagious when they burst (rupture). They stay contagious until they're completely healed. Avoid close contact with others until your cold sore has completely healed and disappeared.

There's no need to stay away from work or miss school if you or your child have a cold sore.

You can help minimise the risk of the cold sore virus spreading and cold sores recurring by:

  • avoid touching cold sores unless you're applying cold sore cream – creams should be dabbed on gently rather than rubbed in, as this can damage your skin further
  • always wash your hands before and after applying cold sore cream and after touching the affected area
  • don't share cold sore creams or medication with other people as this can cause the infection to spread
  • don't share items that come into contact with the affected area, such as lipsticks or cutlery
  • avoid kissing and oral sex until your cold sores have completely healed
  • be particularly careful around newborn babies, pregnant women and people with a low immune system, such as those with HIV or those having chemotherapy
  • if you know what usually triggers your cold sores, try to avoid the triggers – for example, a sun block lip balm (SPF 15 or higher) may help prevent cold sores triggered by bright sunlight


The information on this page has been adapted from original content from the NHS website.

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