Cold sores are small, blister-like lesions that usually appear around the mouth. They are caused by the herpes simplex viruses. The strain that usually causes them around the mouth is herpes simplex type 1 (HSV-1).

In rare cases, cold sores can also be caused by the herpes simplex type 2 virus (HSV-2). This can happen as a result of having oral sex with a man or woman who has genital herpes.

The herpes simplex virus

The herpes simplex virus, or 'cold sore virus', is highly contagious and can be easily passed from person to person by close direct contact. Once someone has been exposed to the virus, it remains dormant (inactive) most of the time.

However, every so often the virus is activated by certain triggers, causing an outbreak of cold sores. The triggers that cause cold sores vary from person to person. Some people have frequently recurring cold sores, two to three times a year for example, while others have one cold sore and never have another. Some people never get cold sores because the virus never becomes active.

Outlook

Cold sores usually clear up without treatment in 7 to 10 days and do not leave a scar. 

Creams and treatments are available over the counter that may help ease the symptoms and speed up the healing time. To be effective, these treatments must be applied as soon as you have signs of a cold sore, such as a burning or tingling sensation.

In most cases, cold sores are mild. In rare cases, they can cause a number of complications.

In newborn babies or people with weakened immune systems, cold sores can be life threatening, although this is rare.

Usually, when you first become infected with the herpes simplex virus (known as the primary infection), there are no symptoms. You may not know that you have contracted the virus until you get an outbreak of cold sores sometime later.

However, if the primary infection causes symptoms, these can be quite severe.

Symptoms of the primary infection

Symptoms of the primary infection are most likely to occur in children under the age of five. They include:

• swollen and irritated gums with small, painful sores in and around the mouth (known as herpes simplex gingivostomatitis, see below)
• sore throat and swollen glands
• producing more saliva than normal
• fever
• dehydration (a lack of water in the body)
• nausea (feeling sick)
• headaches

If you or your child develops herpes simplex gingivostomatitis, it can last 7-14 days and may take up to three weeks for the sores to heal. However, gingivostomatitis does not often recur after the primary infection. It is usually young children who get gingivostomatitis, although it is possible for adults to get it.

Adults

If an adult has a primary infection, it usually presents itself as pharyngotonsillitis (a sore throat and swollen tonsils) or an illness such as glandular fever. The symptoms will usually be a sore throat with or without swollen glands. You may also have halitosis (foul-smelling breath) and painful sores in and around your mouth, which can develop into ulcers with grey or yellow centres.

If someone has been infected with the herpes simplex virus at an early age, it may be triggered periodically in later life, which can cause recurring bouts of cold sores. After the primary infection, the symptoms are usually reduced to just the cold sores themselves.

Symptoms of the recurrent infection (outbreaks of cold sores)

Recurrent infections are normally shorter and less severe than the primary infection. Usually, the only symptom is the outbreak of cold sores, although in some cases 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 appear, most commonly on the edges of your lower lip.

If you have frequent recurrent infections, your cold sores may occur in the same place every time. Your cold sores may grow in size and cause irritation and pain. They may weep and eventually grow a crust or scab within 48 hours of the initial tingling sensation.

Most cold sores disappear within 7-10 days without treatment and they generally heal without scarring.

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 when a child is kissed by a person with a cold sore, such as a family member. The virus goes through the skin and travels up the nerves, where it lies dormant (inactive) until it is triggered at a later date.

Several different factors are thought to trigger outbreaks of cold sores, which can differ between people. The triggers may include:

• emotional upset or psychological stress
• fatigue and tiredness
• an injury to the affected area
• menstruation (periods)
• strong sunlight

In rare cases, cold sores can be caused by the herpes simplex virus type 2 (HSV-2), which usually causes genital herpes. This can happen if you have oral sex with a man or woman who has genital herpes.

If you have had outbreaks of cold sores before, it is likely that you will know what they are if they return. However, if you think that you or your child has a primary infection of the cold sore virus, or your cold sores have not healed after 7-10 days, see your GP.

Cold sores can usually be diagnosed based on their appearance. In some cases, your GP may take a blood sample or a sample of the fluid scraped from your cold sores so that the presence of the cold sore virus can be confirmed with laboratory analysis. However, this is usually only necessary for people who have a damaged immune system, such as people undergoing chemotherapy or who are HIV positive.

The treatments for cold sores and the steps you can take to aid your recovery are detailed below.

There is also information on treating gingivostomatitis, which may need different treatment if you or your child develops it as part of a primary infection.

Creams and patches for cold sores

If used correctly, antiviral cold sore creams may speed up the healing time of a recurrent infection. They usually contain medication known as aciclovir or penciclovir. Brand names include Zovirax.

These creams are widely available over the counter from pharmacies without a prescription. However, they are only effective if you apply them as soon as the first signs of a cold sore appear, when the herpes simplex virus is spreading and replicating itself. Using an antiviral cream after this initial period is unlikely to have much effect.

If you have frequently recurring bouts of cold sores, apply an antiviral cream as soon as you feel the tingling sensation, that indicates that a cold sore is about to develop. You will need to apply the cream up to five times a day for four to five days. However, antiviral creams can only help heal a current outbreak of cold sores. They do not get rid of the virus that causes cold sores or prevent future outbreaks from occurring.

There are also cold sore patches (brand name Compeed) that contain a gel called hydrocolloid, which is an effective treatment for skin wounds. The patch is placed over the cold sore and hides the sore while it heals.

Research suggests that cold sores heal in the same amount of time with either patches or antiviral creams. 

Treating complications

If your cold sores are particularly severe, or you have a damaged immune system (for example because you are having chemotherapy or you have HIV), you may be at risk of further complications, including encephalitis (swelling of the brain) or a spread of your infection to other parts of your body, such as your eyes.

If this is the case, see your GP, who may prescribe antiviral tablets and refer you for specialist treatment. The kind of treatment you will receive will depend on the severity of your cold sores or the particular complication that is causing problems. For example, if you develop herpetic keratoconjunctivitis (a secondary infection that affects the eyes), you may need to see an ophthalmologist (specialist eye doctor).

Non-antiviral treatments for cold sores

Several non-antiviral creams are available over the counter (without a prescription) from pharmacies. These may help ease the irritation of your cold sores. The creams are not made specifically to treat cold sores and will not help them to heal faster, but you may want to try them if your cold sores are painful, dry or itchy. Brand names include Bonjela, Blistex and Cymex.

Pain can be treated with painkillers, such as ibuprofen or paracetamol (both are available in liquid form for young children). Do not take ibuprofen if you are asthmatic or if you have (or have had) stomach ulcers. Children under the age of 16 should not take aspirin.

Speak to your GP if you have cold sores and you are pregnant.

Treatment for gingivostomatitis

If you or your child has gingivostomatitis as a result of the cold sore virus, see your GP, who can suggest treatments to ease the symptoms.

If your infection is painful, your GP may suggest using a preparation that contains benzydamine (available as an oral rinse or spray) to relieve any pain in your mouth or throat.

Brushing your teeth may also be painful because of the inflammation (swelling) of your gums. Your GP may suggest using an antiseptic mouthwash. This will help prevent secondary infections and can help control plaque build-up if you cannot brush your teeth effectively.

As with the treatment of cold sores, any pain or fever can be treated using ibuprofen or paracetamol. However, do not take ibuprofen if you are asthmatic or if you have or have had stomach problems, such as stomach ulcers. Children under the age of 16 should not take aspirin.

In rare cases of gingivostomatitis, it is possible for your lips to become stuck together in places (known as labial adhesions). You can buy a lip barrier cream from your local pharmacist, such as Vaseline or Lypsyl, to prevent this happening.

If you or your child has gingivostomatitis, it is important that you drink plenty of fluids to avoid becoming dehydrated. Young children are particularly at risk as they may refuse to eat or drink due to the pain in their mouth. It is important to watch out for signs of dehydration, which may include:

• headaches
• tiredness
• irritability
• light-headedness
• low urine output

If you or your child become severely dehydrated, hospital treatment may be required. If this is the case, it may be necessary to have fluids administered directly into a vein (intravenously).

In most cases of gingivostomatitis, the infection will run its course in 7-14 days, although it may take up to three weeks for sores to heal completely.

Referral to a specialist

If you or your child still has symptoms of gingivostomatitis after two weeks, or if the infection is severe, return to your GP, who may refer you for specialist treatment.

You may also need to be referred for specialist treatment for gingivostomatitis if you are pregnant or have a damaged immune system. If your newborn baby develops gingivostomatitis, see your GP as they may also need to be referred for specialist treatment.

General tips

• Drink plenty of fluids to avoid dehydration.
• Avoid acidic or salty foods and eat cool, soft foods.
• If brushing your teeth is painful, use an antiseptic mouthwash.
• Dab creams onto sores rather than rubbing it in.
• Wash your hands using soap and water before and after applying cold sore creams.
• Avoid touching your cold sores, other than to apply cream, and do not share your cold sore cream with other people.

• Infections caused by the cold sore virus are often mild and usually heal without the need for treatment. However, in rare cases they can cause complications, particularly in people with damaged immune systems, such as people undergoing chemotherapy or who are HIV positive.

  The possible complications of the cold sore virus are detailed below.

  Dehydration

  Dehydration (a lack of water in the body) may occur as a result of the pain caused by a cold sore. It is easy to neglect the need to drink plenty of fluids if your mouth is painful. Young children are particularly at risk of becoming dehydrated. .

  Herpetic whitlow

  It is possible for the cold sore virus to spread to other parts of your body. This is known as a secondary infection. Herpetic whitlow is a secondary infection of the cold sore virus that causes painful sores and blisters on your fingers. It can occur when the cold sore virus comes into contact with a cut or graze on your hand and enters your skin. However, it can be easily treated using antiviral medication.

  Herpetic keratoconjunctivitis

  Herpetic keratoconjunctivitis is a secondary infection of the cold sore virus that affects your eyes. If the virus comes into contact with your eyes, it can cause inflammation (swelling and irritation) of your eye area and sores to appear on your eyelids. However, it can usually be easily treated using antiviral medication available from a specialist eye doctor.

  If left untreated, herpetic keratoconjunctivitis can cause your cornea (the transparent layer over your eye) to become infected, which can eventually lead to blindness. It is very important not to touch your eyes when you have an active cold sore. However, if you must touch your eyes, for example to remove contact lenses, wash your hands thoroughly first.

  Encephalitis

  Encephalitis is a serious condition in which the brain becomes swollen, possibly causing brain damage and even death. In severe cases it is caused by the cold sore virus spreading to the brain, but this is very rare. Encephalitis can be treated by injecting antiviral drugs, such as aciclovir, into the veins.

  Eczema Herpeticum

  People with some skin conditions such as atopic eczema who suffer an eruption of cold sores can develop more severe skin eruptions when they become badly infected and require oral or intravenous antibiotics.

  It is not possible to completely prevent primary infections or outbreaks of cold sores. Cold sores are at their most contagious when they burst (rupture), but remain contagious until they are completely healed. Therefore, it is important for other people to avoid direct contact with your affected area until your cold sore has completely healed and disappeared.

  However, if you or your child has a cold sore, there is no need for you to stay away from work or for your child to miss school.

  Minimising the spread of the infection

  You can help minimise the spread and recurrence of the cold sore virus by following the advice below:

  • Avoid touching your cold sores unless you are applying a 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 cream and after touching the affected area.
  • Do not share creams or medications with other people because this can cause the infection to spread.
  • Do not 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.
  • If you have a cold sore, be particularly careful around newborn babies, pregnant women and people with a low immune system, such as people having chemotherapy or with HIV.

  Preventing recurrent outbreaks

  If you know what usually triggers your cold sores, try to avoid these triggers if possible. For example, a sun block lip balm (SPF 15 or higher) may help prevent cold sores triggered by bright sunlight.

  Use an antiviral cold sore cream, such as Zovirax, as soon as you feel the tingling sensation that indicates a coming cold sore. However, there is no benefit in using an antiviral cream continuously to try to prevent future cold sores. They cannot cure the virus and will only be effective once the virus has been triggered.