Complications of cold sores 

Infections caused by the cold sore virus are often mild and usually disappear without treatment. However, in rare cases, they can cause complications.

People particularly at risk are those with weak immune systems, such as people who are HIV positive or those having chemotherapy treatment.

Some of the possible complications that can develop as a result of the herpes simplex virus are outlined below.


Dehydration is a lack of water in the body. It can sometimes occur as a result of the pain caused by a cold sore.

It can be easy to not drink enough fluid if your mouth is painful. Young children with cold sores are particularly at risk of becoming dehydrated.

Read more about dehydration.

Secondary infection

It is possible for the cold sore virus to spread to other parts of your body. This is known as a secondary infection. Secondary infections can usually be easily treated with antiviral medication.

Examples of secondary infection 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 inflammation (swelling and irritation) 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 is 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.


Encephalitis is a condition where the brain becomes inflamed and swollen. This can be very serious and can cause brain damage and even death.

In very rare cases, encephalitis 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.

Read more about encephalitis.

Page last reviewed: 10/04/2014

Next review due: 10/04/2016