Cold sore

Cold sores are small blisters that appear on the lips or around the mouth. The herpes simplex virus (HSV) causes them. In most cases a cold sore clears up on its own within 7 to 10 days, without any treatment.

You may have no symptoms at all when you first catch the herpes simplex virus (HSV). This first infection is called the primary infection. Cold sores can appear later as an outbreak, and they may keep coming back (recurrent infection). But if the primary infection does cause symptoms, they can be quite severe.

Children younger than 5 years old are the most likely to have symptoms when they first catch the cold sore virus (the primary infection). These can include:

• swollen and irritated gums with small, painful sores in and around the mouth, which 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 mostly affects young children, though adults can get it too. It can last 7 to 14 days, and the sores may take up to 3 weeks to heal. But gingivostomatitis doesn't usually happen after the primary infection.

Adults rarely have symptoms from the first (primary) infection with the cold sore virus, but when they do, the symptoms are much like those children get.

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 turn into ulcers with grey or yellow centres.

If you catch HSV at an early age, it can be triggered now and then later in life and cause repeated bouts of cold sores. After the primary infection, the symptoms are usually down to just the cold sores themselves.

If you have cold sores, you can get advice and treatment straight from a pharmacy. If needed, the pharmacist may suggest that you speak to your doctor.

• see a doctor if the cold sore has not started to heal within 10 days
• see a doctor if you're worried about a cold sore or think it's something else
• see a doctor if the cold sore is very large or painful
• see a doctor if you or your child have swollen, painful gums and sores in the mouth (gingivostomatitis)
• see a doctor if you have a weakened immune system, for example, because of chemotherapy, diabetes, or HIV

• eat cool, soft foods
• wash your hands with soap and water before and after you apply cream
• avoid anything that triggers your cold sores
• use a sunblock lip balm (SPF 15 or above) if you're outside in the sun
• use an antiseptic mouthwash if brushing your teeth is painful
• take paracetamol or ibuprofen to ease pain and swelling (both come in liquid form for young children), but do not give aspirin to children under 16
• drink plenty of fluids to avoid dehydration

• don't kiss anyone while you have a cold sore
• don't have oral sex until your cold sore has completely healed
• don't touch your cold sore, apart from applying cream, and if you do touch it, wash your hands
• don't rub cream into the cold sore, dab it on instead
• don't eat acidic or salty foods if they make your cold sore feel worse

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

Pharmacies also sell electronic devices that treat cold sores with light or lasers. Some people find them helpful, but there haven't been many studies to confirm whether they work.

If you get cold sores regularly, use antiviral creams as soon as you notice the early tingling feeling. They don't always work once blisters have appeared.

If your cold sores are very large, painful and keep coming back, your doctor 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.

Cold sores are usually caused by the herpes simplex virus type 1 (HSV-1). Most people pick the virus up in early childhood, for example when a family member or friend who has a cold sore kisses the child.

The virus passes through the skin and travels up the nerves. There it lies inactive (dormant) until something triggers it at a later date.

A cold sore outbreak can be set off by a number of things:

• 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

In many cases, though, there's no obvious trigger for an outbreak.

Cold sores can sometimes be caused by herpes simplex virus type 2 (HSV-2). This can happen after 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 area around them.

You can't stop an infection with the herpes simplex virus, and you can't prevent outbreaks of cold sores either. But there are things you can do to limit how far the infection spreads.

A cold sore is most contagious when it bursts (ruptures), though it stays contagious until it has completely healed. So avoid close contact with other people until your cold sore has healed and gone.

You don't need to stay away from work or miss school, though, if you or your child have a cold sore.

Cold sores are usually mild, but in rare cases they cause complications. People with weak immune systems, whether from an illness or from treatments such as chemotherapy, are particularly at risk.

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

Other complications of cold sores include:

• skin infections, which 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), which causes painful sores and blisters on and around your fingers
• herpetic keratoconjunctivitis, which causes swelling and irritation (inflammation) of your eye area and sores on your eyelids