Cold sore (herpes simplex virus) - Causes 

Causes of cold sores 

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 – 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 dormant (inactive) until it is 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 is no obvious trigger for an outbreak.

Occasionally, cold sores can be caused by the herpes simplex virus type 2 (HSV-2).

This can happen after having oral sex with a man or woman who has genital herpes, which is usually caused by HSV-2.

In genital herpes, painful blisters develop on your genitals and the surrounding area.

Page last reviewed: 10/04/2014

Next review due: 10/04/2016

Ratings

How helpful is this page?

Average rating

Based on 125 ratings

All ratings

Add your rating

Comments

Genital herpes

Genital herpes often causes no initial symtoms. At least 80% of people who carry the virus don't know they've been infected.