Cold sore

Cold sores are small blisters that develop on the lips or around the mouth. They’re caused by the herpes simplex virus (HSV) and usually clear up without treatment within 7 to 10 days.

Symptoms of cold sores

You may not have any symptoms when you first become infected with HSV (the primary infection).

An outbreak of cold sores may occur later and keep coming back (recurrent infection).

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

In children

Symptoms of the primary infection are most likely to develop in children younger than 5 years old. These 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 7 to 14 days, with the sores taking up to 3 weeks to heal. However, gingivostomatitis doesn’t usually happen after the primary infection.

In adults

Symptoms of the primary infection are rare in adults but are similar to those experienced by children.

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 HSV at an early age, it may be triggered periodically in later life and can cause recurring bouts of cold sores. After the primary infection, the symptoms are usually reduced to just the cold sores themselves.

When to get medical advice

If you have cold sores you can get advice and treatment directly from a pharmacy.

Your pharmacist may recommend that you speak to your GP if required.

Treatment for cold sores

Things you can do

Treatment from a pharmacist

If you get cold sores, a pharmacist may recommend:

• creams to ease pain and irritation
• antiviral creams to speed up the healing time
• cold sore patches to protect the skin while it heals

You can buy electronic devices from pharmacies that treat cold sores with light or lasers. Some people find these helpful, but there have not been many studies to confirm if they work.

If you regularly get cold sores, use antiviral creams as soon as you recognise the early tingling feeling. They do not always work after blisters appear.

Treatment from a GP

If your cold sores are very large, painful and keep coming back, your GP may prescribe antiviral tablets.

Newborn babies, pregnant women and people with a weakened immune system who have cold sores may be referred to hospital for advice or treatment.

What causes cold sores

Cold sores are usually caused by the herpes simplex virus type 1 (HSV-1).

In most cases, the virus is passed on in early childhood. For example, when a child is kissed by a family member or friend with a cold sore.

The virus passes through the skin and travels up the nerves, where it lies inactive (dormant) until it’s triggered at a later date.

Cold sore triggers

Things that can trigger a cold sore outbreak include:

• having another infection, such as a respiratory tract infection
• having a high temperature (fever)
• emotional upset or psychological stress
• tiredness and fatigue
• an injury to the affected area
• menstruation (periods)
• strong sunlight

However, in many cases, there’s no obvious trigger for an outbreak.

Herpes simplex virus type 2

Sometimes, cold sores can be caused by the herpes simplex virus type 2 (HSV-2).

This can happen after having oral sex with someone who has genital herpes, which is usually caused by HSV-2.

In genital herpes, painful blisters develop on your genitals and the surrounding area.

Preventing infection

It’s not possible to prevent infection with the herpes simplex virus or prevent outbreaks of cold sores. However, there are things you can do to minimise the spread of infection.

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

However, there’s no need to stay away from work or miss school if you or your child have a cold sore.

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.

Dehydration sometimes occurs if drinking fluids becomes painful. Young children are particularly at risk of becoming dehydrated.

Other complications of cold sores include:

• skin infections – these often happen if the virus comes into contact with broken skin, such as a cut or graze, or a skin condition such as eczema
• herpetic whitlow (whitlow finger) – this causes painful sores and blisters to appear on and around your fingers
• herpetic keratoconjunctivitis – this causes swelling and irritation (inflammation) of your eye area and sores to develop on your eyelids