Cold sores are small blisters that develop on the lips or around the mouth. They're caused by the herpes simplex virus and usually clear up without treatment within 7 to 10 days.
You may not have any symptoms when you first become infected with the herpes simplex virus. An outbreak of cold sores may happen some time later.
Cold sores often start with a tingling, itching or burning sensation around your mouth. Small fluid-filled sores then appear, usually on the edges of your lower lip.
Read more about the symptoms of cold sores .
When to visit your doctor
If you've had outbreaks of cold sores before, it's likely that you'll know what they are if they return.
You only need to visit your doctor if you're unsure whether it's a cold sore or if it's severe and spreading further than just the lip. See your doctor if a cold sore hasn't healed after 7 to 10 days.
What causes cold sores?
The herpes simplex virus is responsible for cold sores. There are two strains, known as HSV-1 and HSV-2.
Read more about the causes of cold sores .
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. After someone has contracted the virus, it remains inactive (dormant) most of the time.
However, every so often the virus can be activated by certain triggers, resulting in an outbreak of cold sores. These triggers vary from person to person, but can include sunlight, fatigue, an injury to the affected area, and, in women, their period .
Some people have frequently recurring cold sores around two or three times a year, while others have one cold sore and never have another. Some people never get cold sores at all because the virus never becomes active.
Treating cold sores
Cold sores usually clear up by themselves without treatment within 7 to 10 days.
However, antiviral creams are available over the counter from pharmacies without a prescription. If used correctly, these can help ease your symptoms and speed up the healing time.
To be effective, these treatments should be applied as soon as the first signs of a cold sore appear – when you feel a tingling, itching or burning sensation around your mouth. Using an antiviral cream after this initial period is unlikely to have much of an effect.
Cold sore patches are also available that contain hydrocolloid gel, which is an effective treatment for skin wounds. The patch is placed over the cold sore while it heals.
Antiviral tablets may be prescribed for severe cases.
Read more about treating cold sores .
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.
The herpes simplex virus can also spread to other parts of your body. Examples of when this can occur include:
- skin infections – these often occur 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
Left untreated, herpetic keratoconjunctivitis can cause the cornea, the transparent layer at the front of your eye, to become infected, which can eventually lead to blindness.
It's therefore important not to touch your eyes if you have an unhealed cold sore. If you must touch your eyes – for example, to remove contact lenses – wash your hands thoroughly first.
In very rare cases, encephalitis , a condition where the brain becomes inflamed and swollen, can be caused by the cold sore virus spreading to the brain. It can be treated with intravenous injections of antiviral medications, such as aciclovir.
It's not possible to prevent infection with the herpes simplex virus or prevent outbreaks of cold sores, but you can take steps 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.
You can help minimise the risk of the cold sore virus spreading and cold sores recurring by following the advice below:
- avoid touching cold sores unless you're applying cold sore 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 cold sore cream and after touching the affected area
- don't share cold sore creams or medication with other people as this can cause the infection to spread
- don't 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
- be particularly careful around newborn babies, pregnant women and people with a low immune system, such as those with HIV or those having chemotherapy
- if you know what usually triggers your cold sores, try to avoid the triggers – for example, a sun block lip balm (SPF 15 or higher) may help prevent cold sores triggered by bright sunlight
Symptoms of cold sores
You won't usually have any symptoms when you first become infected with the herpes simplex virus (the primary infection).
An outbreak of cold sores may occur some time later and keep coming back (recurrent infection).
However, if the primary infection does cause symptoms, they can be quite severe.
Herpes simplex virus primary infection
Symptoms of the primary infection are most likely to develop in children younger than five years old. Symptoms 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
- feeling sick (nausea)
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 three weeks to heal. However, gingivostomatitis doesn't usually recur after the primary infection.
Primary herpes simplex viruses are rare in adults, but the symptoms 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 the herpes simplex virus 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.
Recurrent infections (cold sores)
Recurrent infections usually last for less time and are less severe than the primary infection. The only symptom is an outbreak of cold sores, although 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 develop, usually on the edges of your lower lip.
If you have frequent recurrent infections, you may develop cold sores in the same place every time. They may grow in size and cause irritation and pain. Initially, they may ooze before crusting or scabbing over within 48 hours of the initial tingling sensation.
If the cold sores are very troublesome, it's possible to suppress them by taking an antiviral tablet called acyclovir regularly, every day for a few months. This is usually only recommended if cold sores are causing a lot of problems, and they may come back when treatment is stopped.
Most cold sores disappear within 7 to 10 days without treatment and usually heal without scarring .
Causes of cold sores
Cold sores are usually caused by the herpes simplex virus.
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
Factors thought to trigger outbreaks of cold sores 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.
Cold sores can happen after having oral sex with a man or woman who has genital herpes .
Treating cold sores
Cold sores usually clear up without treatment within 7 to 10 days. Antiviral tablets or cream can be used to ease your symptoms and speed up the healing time.
If you develop a cold sore, some general advice to follow includes:
- 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 on to sores rather than rubbing them 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 don't share your cold sore cream with others
Antiviral creams and tablets
Antiviral creams such as aciclovir or penciclovir (also known as Fenistil) may speed up the healing time of a recurrent cold sore infection if used correctly.
Cold sore creams are widely available over the counter from pharmacies without a prescription.
They're 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. Using an antiviral cream after this initial period is unlikely to have much effect.
If you have frequently recurring bouts of cold sores, use antiviral medication as soon as you feel the tingling sensation that indicates a cold sore is about to develop. You'll need to apply the cream up to five times a day for four to five days.
Antiviral creams can only help to heal a current outbreak of cold sores. They don't get rid of the herpes simplex virus or prevent future outbreaks of cold sores occurring.
Antiviral tablets are generally more effective than creams at treating cold sores, but are usually only prescribed for more severe cases.
Cold sore patches
Cold sore patches that contain a special gel called hydrocolloid are also available. They're an effective treatment for skin wounds and are placed over the cold sore to hide the sore area while it heals.
Several non-antiviral creams are also available over the counter from pharmacies without the need for a prescription.
These creams aren't specifically designed to treat cold sores and won't help them heal faster, but they may help ease any pain or irritation. Ask your pharmacist to recommend a suitable treatment for you.
Children under the age of 16 shouldn't be given aspirin.
Speak to your doctor if you have cold sores and you're pregnant.
If your cold sores are particularly severe or your immune system is damaged – for example, if you have HIV or you're having chemotherapy treatment – you may be at risk of developing serious complications.
For example, your risk of developing encephalitis or the infection spreading to other parts of your body, such as your eyes, is increased.
Visit your doctor if you're at risk. They may prescribe antiviral tablets and refer you for specialist treatment.
The type of treatment recommended will depend on the severity of your cold sore symptoms and the complication that's causing problems.
For example, if you develop herpetic keratoconjunctivitis – a secondary eye infection – you may need to see an ophthalmologist, a specialist eye doctor.
Visit your GP if you or your child develops swollen, painful gums (gingivostomatitis) as a result of the primary herpes simplex infection. They'll be able to suggest treatments to help ease your symptoms.
If the infection is painful, your doctor may suggest using a preparation that contains benzydamine, which is available as an oral rinse or oral spray, to help relieve any pain in your mouth or throat.
Brushing your teeth may also be painful because of the swelling of your gums. Your doctor may suggest using an antiseptic mouthwash. This helps prevent secondary infections and will also control a build-up of plaque if you can't brush your teeth effectively.
As with the treatment of cold sores, any pain or fever can be treated using ibuprofen or paracetamol.
In rare cases of gingivostomatitis, it's possible for your lips to become stuck together in places. Using a lip barrier cream available from your local pharmacist will help prevent this.
If you or your child has gingivostomatitis, it's important to drink plenty of fluids to avoid becoming dehydrated. Young children are particularly at risk as they may refuse to eat or drink because of the pain in their mouth.
It's important to watch out for signs of dehydration , such as:
- low urine output
Most cases of gingivostomatitis get better in 7 to 14 days, although it may take up to three weeks for the sores to heal completely.
If you or your child still has symptoms of gingivostomatitis after two weeks or the infection is severe, go back to your doctor, who may refer you for specialist treatment.
Specialist referral may also be needed for gingivostomatitis if you're pregnant or have a weakened immune system.
Visit your doctor if you have a newborn baby who develops gingivostomatitis, as they may also need to be referred for specialist treatment.