Herpes simplex virus type 1

The most common of infection by herpes simplex virus type 1 (HSV1) are cold sores. These are ulcers of the skin or mucous membranes (the thin moist lining of many parts of the body such as the nose, mouth, throat and genitals).

Although HSV1 infection can occur at any age, most people get their first infection in early childhood; frequently symptoms are mild or absent. After the first infection, the virus remains latent (resting) in nerve cells in the brain or spinal cord and is present for life. If the virus becomes active again it results in cold sores: painful clear blisters (see image) on a red base, usually on the face or lips. The blisters crust and heal within a few days. The virus can be triggered to become active again by physical or emotional stress, sunlight, a viral infection or hormonal changes. Appearance of the blisters is often preceded by tingling, itching and pain at the site.

Image courtesy Public Health Image Library (PHIL), Department of Health and Human Services, Centers for Disease Control and Prevention (CDC-USA) Dr Herrmann.

Herpes simplex virus type 1


Herpes simplex virus infection can be diagnosed by scraping the base of the cold sore and examining cells under the microscope, by growing the virus, or by a PCR (polymerase chain reaction) test in a pathology laboratory. Blood tests are not usually helpful in diagnosis. About 80% of adults in Australia have antibodies to HSV1 and 25% have antibodies to HSV2.

Incubation period

(time between becoming infected and developing symptoms)

2 to 12 days.

Infectious period

(time during which an infected person can infect others)

Spread of infection is most likely when a moist blister is present. However, people with a history of cold sores may shed the virus in their saliva and are therefore capable of infecting others even without a blister being present.


Topical therapy (cream or ointment) is available through pharmacies without a prescription. Oral (by mouth) antiviral therapy is restricted to severe cases and requires a doctor’s prescription. The cost is not covered by the Pharmaceutical Benefits Scheme for herpes simplex infections.


  • Young children unable to follow good hygiene practices should be excluded from childcare, preschool or school while the cold sore is weeping
  • cold sores should be covered with a dressing where possible
  • follow good hand washing techniques
  • do not kiss on or near the cold sore
  • do not perform oral sex if cold sores are present
  • do not share food or drink containers
  • dispose of used tissues correctly.

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