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Cold Sores (Herpes Simplex)

What are cold sores?

Cold sores are small blisters that develop on and around the lips. The blisters are filled with fluid. Cold sores are also called fever blisters. Cold sores are a common condition caused by a virus. Cold sores cannot be cured. Your child can take steps to have them less often and for a shorter time.

For most children, the virus only causes sores around the mouth. The sores may be painful but will go away. They often come back. Some children can become very sick from the virus. Those particularly at risk include newborn babies, children with weak immune systems, and children with eczema.

Signs and symptoms of cold sores

The first infection is usually the most severe. The child’s gums, palate, and tongue become red and swollen. They become covered with blisters. The child often has a high fever. He may be very irritable. He may refuse to eat or drink because of pain. Symptoms usually last 7 to 14 days. Some children need pain medication. They may rarely require admission to the hospital for help with pain and dehydration.

The virus becomes inactive in nerve cells. It may start again in the form of cold sores: about 4 to 12 hours before the actual blisters appear on your child’s skin, there will be a tingling sensation around the infected area. One blister or a few small blisters surrounded by red and inflamed skin will appear in that area. The blisters will be itchy or sore. They will likely burst within a few days. The clear fluid will then form a crust. The sore will heal on its own, without scarring, within a week.

Usually the blisters appear around the mouth or on the lips. Sometimes they can also appear on other areas of the skin, eyes, and fingers.


A virus called herpes simplex type 1 causes cold sores. Another type of virus, herpes simplex type 2, is usually responsible for genital herpes, but it can also cause sores on the face.

Children usually get infected by coming in close contact with saliva or open lesions of an infected person. If your child has a cold sore, they should avoid close contact with babies, children with eczema, or people with a weak immune system. However, people who carry the virus and do not have obvious cold sores can infect others.

Once your child has been infected, the virus lies inactive in the nerve cells of the skin. Over-tiredness, a weak immune system, chapped lips, fever, menstruation, stress, or exposure to the sun may trigger an outbreak. Most people will get recurrent cold sores from the same trigger.

There is no cure for cold sores. Your child will likely have the sores throughout life. The frequency varies. Some people get cold sores as often as once a month. Some only get them once or twice a year.


The following complications can occur but are rare:

  • dehydration and severe pain
  • eye infections
  • severe skin infections, usually in people with underlying skin diseases like eczema

Infection of other organs like the brain or liver may occur, more commonly in young babies or people who have weak immune systems. These can cause severe illness or death.

What your child’s doctor can do for cold sores

Pain medications may be prescribed. Anti-viral medications may be helpful if it is diagnosed early. In general, cold sores clear up without treatment in 3 to 7 days. Your child’s doctor may prescribe a treatment to rub on the skin. But this type of treatment is only effective when applied to the skin at the first sign of infection.


Your child can take the following steps to guard against cold sores, prevent spreading them to other parts of the body, or to avoid spreading the virus to another person:

  • Avoid kissing and skin contact with people while blisters are present.
  • Avoid sharing items like food utensils and lip balm that can spread the virus.
  • Keep hands clean.
  • Be careful about touching other parts of the body, especially the eyes and genital area.
  • Avoid triggers such as undue stress, getting a cold or flu, a lack of sleep, and over-exposure to the sun.
  • Use sunblock.

When to seek medical assistance

See a doctor if you notice any of the following:

  • blisters or pain in or around the eye
  • high fever
  • confusion or change in behaviour
  • if your child appears very unwell or is not drinking well
  • blisters anywhere on the body if the baby or child has a weak immune system

Key points

  • Cold sores are very common and contagious.
  • There is no cure for cold sores. They can be prevented and controlled.
  • The first episode is usually the most severe.
  • Your child may require an antiviral medication or an ointment to rub on his skin.

Sheila Jacobson, MBBCh, FRCPC