Cold Sores (Herpes Simplex)
What is herpes simplex?
Herpes simplex is a common viral infection that presents with localised blistering. It affects most people on one or more occasions during their lives.
Herpes simplex is commonly referred to as cold sores or fever blisters, as recurrences are often triggered by a febrile illness, such as a cold.
What causes herpes simplex?
Herpes simplex is caused by one of two types of herpes simplex virus (HSV), members of the Herpesvirales family of double-stranded DNA viruses.
- Type 1 HSV is mainly associated with oral and facial infections
- Type 2 HSV is mainly associated with genital and rectal infections (anogenital herpes)
However, either virus can affect almost any area of skin or mucous membrane.
After the primary episode of infection, HSV resides in a latent state in spinal dorsal root nerves that supply sensation to the skin. During a recurrence, the virus follows the nerves onto the skin or mucous membranes, where it multiplies, causing the clinical lesion. After each attack and lifelong, it enters the resting state.
During an attack, the virus can be inoculated into new sites of skin, which can then develop blisters as well as the original site of infection.
Who gets herpes simplex?
Primary attacks of Type 1 HSV infections occur mainly in infants and young children. In crowded, underdeveloped areas of the world, nearly all children have been infected by the age of 5. In less crowded places, the incidence is lower; for example, less than half of university entrants in Britain have been infected. Type 2 HSV infections occur mainly after puberty and are often transmitted sexually.
HSV is transmitted by direct or indirect contact with someone with active herpes simplex, which is infectious for 7–12 days. Asymptomatic shedding of the virus in saliva or genital secretions can also lead to transmission of HSV, but this is infrequent, as the amount shed from inactive lesions is 100 to 1000 times less than when it is active. The incubation period is 2–12 days.
Minor injury helps inoculate HSV into the skin. For example:
- A thumb sucker may transmit the virus from their mouth to their thumb.
- A health-care worker may develop herpetic whitlow
- A rugby player may get a cluster of blisters on one cheek (‘scrumpox’).