Cold sores are common in children and are caused by herpes simplex virus-1 (HSV-1).  Another type of herpes virus (HSV-2) is responsible for the majority of sexually-transmitted "herpes" cases.  As the name implies, cold sores often occur when a child is sick for another reason (i.e., with the common cold).

What causes cold sores?

Herpes simplex virus-1 (HSV-1) causes cold sores.  HSV-1 is also an important cause of more serious illnesses in infants such as skin and central nervous system infections. 

Is a cold sore "herpes"?

The term "herpes" is typically used to describe a different type of HSV virus, HSV-2.  HSV-2 causes the majority of genital infections and is considered a sexually transmitted disease (STD).  There are some similarities in HSV-1 and HSV-2 infections, however HSV-2 typically occurs in the genital area while HSV-1 is the most common cause of lesions on the face and near the mouth (i.e., cold sores).

How common are cold sores, and who gets them?

Cold sores are very common in adults and children.  Once someone is infected with the HSV-1 virus, the virus hides in the nerves where it can cause recurrent infections.  It is estimated that 1 out of 3 adults are carriers of the HSV-1 virus and many of these people were first infected as children.

What are the symptoms of HSV-1 infection?

The first infection or "primary" infection with HSV-1 usually occurs with NO symptoms.  Most people who carry the virus do not know when or how they became infected. Occassionally the primary infection may cause a large area of painful blisters on the skin or inside the mouth and eyes. 

Recurrent infections typically present with blister-like sore that occurs near or inside the mouth.  The site typically begins with a itchy or tingling feeling, with a small grouping of blisters occurring within 1 day.  The blisters pop within about 2 days and form an painful sore that heals completely within about 10 days.  Recurrent infections typically occur in the same area as previous lesions because the virus hides in the nerves that supply that skin area.

Neonatal infections typically occur when an infant is exposed to the virus during or shortly after birth.  The virus may cause a blistering lesion on the skin anywhere on the body.  Infants with fever and a known exposure to the virus should be checked for HSV-1 since they can develop a severe central nervous system infection.

How is HSV-1 infection diagnosed?

In most cases, HSV-1 infection is diagnosed when a child develops the typical skin lesion and no tests are necessary.

In complex cases and for infants, suspicious lesions can be scraped with a cotton swab or microscope slide to be tested in a laboratory.  Body fluids (i.e., blood or spinal fluid) can be tested for the virus with rapid tests or culturing.

How are cold sores treated?

Cold sores may be treated with an oral medicine such as acyclovir or valacyclovir.  These medicines work best when taken at the first sign of a developing cold sore (i.e., a itchy, tingling sensation in a typical location).  Taking the medicine should make the lesion less severe and help it heal more quickly. 

Topical creams and ointments typically don't work very well, but may make the lesion less itchy and painful.

How are cold sores prevented?

Once a child is infected with the HSV-1 virus, they will become carriers of the virus for life.  There is no cure for HSV-1.  This helps explain why nearly a third of adults carry the virus.  Many children will not have noticeable recurrent infections, however some will develop cold sores on a regular basis.

For some people with severe, frequent infections, medicines can be given on a daily basis to prevent HSV-1 reactivation.  This is rarely necessary and often not recommended because the medicines have known side effects.

Photo - This is a close-up of a herpes simplex lesion of the lower lip on the 2nd day after onset. Also known as a cold sore, this lesion is caused by the contagious herpes simplex virus Type-1 (HSV-1), and should not be confused with a canker sore, which is not contagious. The HSV-1 virus remains in the body throughout an exposed person’s entire life. CDC/ Dr. Hermann. 1964. Used with permission.