What causes cold sores?
Cold sores are usually caused by the herpes simplex virus type 1 (HSV1). Most people are exposed to HSV1 in childhood, usually from an infected friend or family member, although only about 30% will ever go on to show symptoms. As part of the herpes simplex family of viruses, HSV1 is not curable and may recur. When not active, the virus hides inside nerve cells until reemerging during the next outbreak.
Although less common, cold sores can also be caused by herpes simplex virus type 2 (HSV2), generally known as genital herpes.
Once the virus is present, many factors may contribute to triggering an outbreak, including but not limited to the following:
- Stress and fatigue
- Illness, including colds and flu
- Hormonal fluctuations during menstruation or pregnancy
- Immune system deficiencies
- Food allergies
- Trauma to the mouth area, including dental work
- Sunlight or exposure to ultraviolet lamps
How are cold sores transmitted?
Like all herpes simplex viruses, cold sores are highly contagious and transmitted through skin-to-skin contact. Cold sores caused by HSV1 are typically transmitted through mouth-to-mouth contact, such as kissing.
HSV2 (genital herpes) can also cause cold sores. In this case, transmission is usually through genital-to-mouth contact during oral sex. The reverse is also possible, with an HSV1 cold sore being transmitted to a partner’s genitals via mouth-to-genital contact.
The virus is most contagious during an outbreak, particularly when blisters are oozing, but may be transmitted even when the virus is dormant. Avoid direct contact whenever an active cold sore outbreak is present.
You can further prevent transmission by avoiding sharing items such a toothbrush, towel, lip balm and utensils. Washing your hands carefully after touching an affected area may also help. Antiviral medications may reduce the rate of HSV transmission but do not eliminate the risk.