Cold sores (oral herpes)

This factsheet is for people who have cold sores, or who would like information about them.

Cold sores are small, fluid-filled blisters that develop around the lips or inside the mouth. They are caused by the herpes simplex virus (HSV), which is passed on through skin-to-skin contact such as kissing.

About cold sores

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. Both types of HSV can cause sores to develop on your face or genitals.

From the first time you get HSV, which is known as the primary infection, it stays in your body for the rest of your life. About eight in 10 people have HSV.

Symptoms of cold sores

The primary HSV infection can develop in different ways. It may cause mild symptoms or no symptoms at all. Children under five are most likely to feel unwell from the primary infection. For example, your child may have:

• a high temperature
• a headache
• swollen and painful gums (gingivitis)
• a sore throat (pharyngitis)
• blisters inside his or her mouth

The blisters inside your child’s mouth usually appear between one and three weeks after he or she gets the virus. They can sometimes take up to three weeks to heal.

In adults, the primary infection may cause a glandular fever-type illness, with symptoms such as a sore throat, swollen tonsils, fever and headache.

After you have had the primary infection (with or without symptoms), the virus lies dormant (inactive) in your body. It moves into your nerve cells, but can become active again. This is known as a recurrent infection and causes blisters to develop on your lips. These blisters are commonly called cold sores and usually heal within five to 10 days.

A cold sore outbreak usually starts with a tingling sensation, redness and swelling around your lip. Then, small, fluid-filled blisters form, which break open and develop a yellow crust (scab). The scab usually falls off around seven days later. Recurrent outbreaks usually occur in or around the same place each time. It's possible to have several a year.

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, don’t improve within seven days, or you have recurrent outbreaks, see your GP for advice.

Complications of cold sores

Complications of cold sores can include the following.

• Dehydration. Young children are especially at risk if they have sores in and around their mouth.
• Impetigo. This is a condition that can develop if the sores become infected with bacteria, causing them to become crusty and yellow.
• Skin infection. HSV can spread into broken skin (for example, eczema or dermatitis) and cause a serious skin infection.
• Eye infection. If HSV infects your eyes, it can seriously damage your vision.

If you have symptoms of either primary or recurrent HSV infection and you have a weakened immune system (if you have HIV/AIDS or are taking medicines that suppress your immune system), you should see your GP. This is because there is a risk that the virus may cause a serious illness.

Although rare in the UK, there is a risk that women can pass the HSV infection to your baby in pregnancy, during the birth or immediately after birth. This is known as neonatal herpes and can cause your baby to be seriously ill. This is more of a problem if you have genital herpes. If you have any symptoms of a primary HSV infection or cold sores for the first time when you are pregnant (particularly in the later stages of pregnancy), you should see your GP or obstetrician for advice.

Causes of cold sores

Cold sores are usually caused by HSV-1. The infection is passed on through skin-to-skin contact, for example by kissing someone who has the virus or by sharing objects that have been in contact with the virus, such as a razor or a lipstick.

There are several factors that can trigger cold sores, including:

• emotional stress
• tiredness or feeling run down
• menstruation
• overexposure to the sun
• having an injury to your mouth or a dental procedure
• a fever

For many people, however, the trigger is unknown.

Diagnosis of cold sores

Usually, your GP will be able to recognise cold sores by looking inside and around your mouth. He or she may take a swab from the blister and send it to a laboratory to be tested. This is to confirm that the infection has been caused by HSV.

Treatment of cold sores

Treatment for cold sores usually involves self-help measures to ease your symptoms. There isn’t a treatment that can get rid of HSV. Once you’re infected, it will remain in your body even if you never get any symptoms.

Self-help

An over-the-counter antiviral cream can help cold sores clear up more quickly, particularly if you apply it when you first notice the symptoms. If you have any pain or discomfort, you can take over-the-counter painkillers, such as paracetamol or ibuprofen. Children can take liquid painkillers. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

If you (or your child) have severe blistering in your mouth and gums, the following steps may help ease any pain or discomfort.

• Drink enough fluids to prevent dehydration; this is particularly important in young children.
• Eat cool, soft foods and avoid salty, acidic or spicy foods.
• Use a lip barrier cream (such as Vaseline) to stop your lips sticking together.

Medicines

If the infection is particularly severe, or frequent, your GP may prescribe a treatment, such as:

• a cream or ointment to help relieve any pain
• a mouthwash to help maintain good oral hygiene
• an antiviral cream (aciclovir or penciclovir) to help clear the infection
• antiviral tablets (acyclovir or valacyclovir) to take daily

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, there are steps you can take to help stop them spreading to other parts of your body and to other people. Some examples are listed below. 

• Try not to touch the sores, but 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 someone, or have oral sex, until your cold sores have completely healed.
• Don't share any objects, such as a lipstick or lip gloss, a razor, face towel or cutlery that may have touched your cold sores.

There are also some measures you can take to prevent yourself getting cold sores. Some examples are listed below.

• Use sunscreen (SPF 15 or higher) on your lips to stop overexposure to sunlight.
• Don't kiss, or have oral sex, with someone who has a cold sore or genital herpes.
• Don't share any creams, medicines or make-up, with someone who has a cold sore.

Stress and feeling run down can trigger recurrent episodes of cold sores. Taking measures to prevent yourself feeling this way can also help reduce your risk of having an outbreak. 
 

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.