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Cold sores (oral herpes)

Key points

  • You will usually feel a tingling sensation, redness and swelling around your lip before a cold sore develops.
  • There are several factors that can trigger cold sores, including being stressed and run down.
  • Cold sores usually heal without any treatment within seven to 10 days.

Cold sores are small, fluid-filled blisters that develop around your lips or inside your mouth

About cold sores

Cold sores are a result of an infection with the herpes simplex virus (HSV). There are two types of HSV: HSV-1 and HSV-2. Most cold sores are caused by HSV-1, whereas most genital sores (genital herpes) are caused by HSV-2. However, both types of HSV can cause sores to develop on your face or genitals.

About eight in 10 people are infected with HSV-1 by the time they are adults but many will have had no symptoms. The first time you get infected with HSV is known as the primary infection. Your symptoms will probably be more severe during the primary infection. This is most likely to happen when you're a child. The virus will then stay in your body for the rest of your life. It moves into your nerve cells and lies dormant (inactive) but can become active again. If this happens, it's called a recurrent infection.

Most people who get recurrent cold sores will have attacks two to three times each year. Some people get cold sores every month. However, the majority of people who have been infected don't get any recurrence.

Symptoms of cold sores

Primary infection symptoms

The primary HSV infection can affect people in different ways.

Symptoms of a primary infection in children include:

  • a fever
  • feeling sick
  • a headache
  • swollen and painful gums (gingivitis)
  • white blisters inside their mouth, followed by yellow ulcers

In adults, the primary infection may cause an illness similar to glandular fever. You can get symptoms such as:

  • a sore throat
  • swollen tonsils
  • a fever
  • a headache

You may also get swollen and painful gums and mouth ulcers.

Recurrent infection symptoms

The main symptom of a recurrent infection is cold sores that usually develop on your lips or around your mouth. You may also get them on your face.

You will usually feel a tingling sensation, redness and swelling around your lip before a cold sore develops. Then small, fluid-filled blisters will form, which break open and develop a crust (scab). The scab usually falls off about seven to 10 days later. Colds cores can be painful for a few days.

Recurrent cold sores usually occur in or around the same place each time.

You probably won’t need to see your GP if you have these symptoms as you can usually manage them at home. However, if they get worse or don’t improve within about seven days, see your GP for advice.

Also see your GP if you have symptoms of a HSV infection and have a weakened immune system. For example, this could be because you have HIV/AIDS or are taking medicines, such as steroids, that suppress your immune system. It's important to see your GP because there is a risk that HSV may cause serious complications.

Complications of cold sores

Complications of cold sores can include the following.

  • Eye infection. If HSV infects your eyes, it can seriously damage your vision, so it’s important to seek medical help.
  • Dehydration. Young children are especially at risk if they have sores in and around their mouth because it can be painful to drink.
  • Eczema herpeticum. This is a severe rash and fever that can develop if you have a type of eczema (called atopic eczema) and are infected with HSV.
  • Paralysed face. If the nerves in your face get infected with HSV, it can temporarily numb the muscles in your face.

Causes of cold sores

Cold sores are caused by HSV – usually HSV-1. You can pass on the virus through skin-to-skin contact, such as kissing. This can happen if you have a cold sore. You can also pass the virus on when you don't have symptoms (but the virus is active), through your saliva.

You're more likely to pass on the virus when you have a cold sore. You will continue to be contagious until it has healed.

There are certain factors that can trigger a recurrence of the virus and cause cold sores. These include:

  • emotional stress
  • being tired or run down
  • hormones – for example, women can get a cold sore before their period
  • exposure to the sun
  • an injury to your mouth or a dental procedure
  • having a cold

Diagnosis of cold sores

If you see your GP, he or she will usually be able to recognise cold sores by looking inside and around your mouth. Most people don't need to have any tests.

However, your GP may take a swab from your cold sore blister and send it to a laboratory to be tested. This is to confirm that the infection is caused by HSV.

Treatment of cold sores

Cold sores usually heal without any treatment within seven to 10 days.


If you use an over-the-counter antiviral cream, such as aciclovir (eg Zovirax), it may help cold sores clear up more quickly. It's important to apply it as soon as you first notice symptoms. If you're pregnant, check with your GP before you use an antiviral cream.

If you have any pain or discomfort, you can take over-the-counter painkillers, such as paracetamol or ibuprofen. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

Remember to drink enough fluids to prevent dehydration; this is particularly important for young children. It might help to moisten your lip with petroleum jelly (eg Vaseline) to stop your lips sticking together.

A special type of laser treatment may help to reduce pain and the number of colds sores you get. You can buy a device from a pharmacy but there isn’t enough evidence yet to say whether or not it's effective.


If you have a particularly severe HSV infection, or have a weakened immune system, your GP may prescribe you antiviral tablets (aciclovir or valaciclovir).

If you have a sore mouth, your GP may prescribe you a mouthwash to help with the pain.

Always ask your GP for advice and read the patient information leaflet that comes with your medicine.

Prevention of cold sores

If you have cold sores, it's important to take steps to help stop them spreading to other parts of your body and to other people. Some examples are listed below.

  • Try not to touch cold sores. If you do, make sure you wash your hands thoroughly with soap and water. If you wear contact lenses, it’s particularly important to wash your hands before you touch them.
  • Don't kiss anyone or have oral sex until your cold sores have completely healed.
  • Don't share any objects, such as lipsticks or lip gloss, razors, face towels or cutlery that may have touched your cold sores.
  • Use tissues to dry your mouth after washing and brushing your teeth, and dispose of these straight away.

You may also be able to avoid some triggers of cold sores. For example, use sunscreen (SPF 15 or higher) on your lips when you're in the sun. If you get cold sores when you're run down, make sure you get plenty of rest. You can also help your immune system, for example by eating healthily and not drinking alcohol or smoking.

By tackling the triggers, it may help to reduce your risk of developing a cold sore.

Reviewed by Rachael Mayfield-Blake, Bupa Health Information Team, January 2014.

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For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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