Viral

Oral herpes (HSV-1)

The cold sore virus. About two in three people under 50 carry it, and it is a growing cause of genital herpes.

Oral herpes or genital herpes?

HSV-1 and HSV-2 are two related viruses. HSV-1 usually lives around the mouth and causes cold sores, and HSV-2 usually lives around the genitals. Either can infect either place: oral sex can carry HSV-1 to the genitals, where it flares up less often than HSV-2 does. Having HSV-1 does not stop you catching HSV-2.

Learn more about Genital herpes (HSV-2)

Not in the calculator

Oral herpes is not in the calculator. Nobody has measured the chance of passing HSV-1 on in a single kiss or sex act, so any per-encounter figure would be a guess. The risk is highest while a cold sore is present, but the virus can also pass on from skin that looks normal.

Cause

Virus (HSV-1)

Carriers

About 2 in 3 people under 50

Curable

No, lifelong but usually mild

Vaccine

Overview

Herpes simplex virus type 1 (HSV-1) is the usual cause of cold sores around the mouth. WHO estimates that about two in three people under 50 carry it, and most caught it as children through everyday contact with someone's saliva, not through sex. It stays in the body for life and can flare up as cold sores now and then, though many people never notice anything. People who already have HSV-1 are not at risk of catching it again, and having it does not protect against HSV-2. HSV-1 can also reach the genitals, mostly through oral sex, and it causes a growing share of new genital herpes, especially in young women and in men who have sex with men.

How it spreads

Kissing and other contact with the mouth, most of all while a cold sore is present
Oral sex, the main way HSV-1 reaches the genitals
Skin that looks normal can still pass it on, though less often than an active sore
Rarely, mother to baby during birth

Symptoms

Many people have no symptoms at all
Tingling or itching around the lips before a cold sore appears
Small blisters on or around the lips that burst and crust over
Blisters or sores on the genitals, if the infection is genital
Rarely, an eye infection (keratitis) or a brain infection (encephalitis)

Most people with HSV-1 do not know they have it, and it can be passed on when there is no sore. A blood test can find HSV-1 antibodies, but it misses some infections and cannot tell whether the virus is in the mouth or the genitals, so it is not part of a routine STI screen.

Vaccine

No vaccine is currently available for Oral herpes (HSV-1).

Treatment

There is no cure, but cold sores usually heal on their own. Antiviral creams or tablets (aciclovir, valaciclovir) can shorten an outbreak if started early, and a doctor or pharmacist can advise on them. Avoid kissing and oral sex while a cold sore is present, because that is when it spreads most easily.

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Educational purposes only. Consult a healthcare provider for personal medical advice.