Cold sore

A cold sore is a small blister (or cluster of blisters) that appears on or around the lips. It's caused by the herpes simplex virus, usually type 1 (HSV-1). Cold sores are incredibly common — most people catch the virus during childhood — and they come back from time to time. The reason they appear in a sex education glossary is that the virus can be passed to the genitals through oral sex.

• Cold sores are caused by the herpes simplex virus (usually HSV-1).
• They're extremely common — most people in the UK carry the virus, though not everyone gets visible sores.
• The virus stays in your body for life and can reactivate, causing sores to come back.
• Cold sores can be passed to the genitals through oral sex, causing genital herpes.
• They're most contagious when a sore is visible, but can sometimes be passed on without one.

How common they are

The majority of people in the UK carry HSV-1 — estimates suggest around 50-80% of adults. [CHECK: current UK prevalence] Most people catch it as children, often from a kiss from a family member. Many people carry the virus without ever getting a visible cold sore. When sores do appear, they usually start with a tingling or itching feeling, then develop into blisters that crust over and heal within 1-2 weeks.

Cold sores tend to come back during times of stress, illness, tiredness, or sun exposure. Some people get them frequently, others rarely or never.

The link to genital herpes

This is the important bit for sex education. HSV-1 (the cold sore virus) can be transferred to someone's genitals through oral sex. If you give oral sex while you have an active cold sore, you can pass the virus to your partner's genitals, where it causes genital herpes. This is actually one of the most common ways people get genital herpes now.

The risk is highest when a cold sore is visible (from the tingling stage through to fully healed), but the virus can occasionally be passed on even when there's no sore present — this is called asymptomatic shedding.

What to do about it

If you have a cold sore, avoid kissing and oral sex until it's completely healed. That's the simplest way to prevent passing it on. Using a condom or dental dam during oral sex reduces the risk but doesn't eliminate it completely, since the sore may be on skin that isn't covered.

Antiviral creams (like aciclovir) can speed up healing if applied early — when you first feel the tingle. These are available over the counter at pharmacies. For people who get cold sores frequently, a GP can prescribe antiviral tablets.

Things people get wrong

"Cold sores aren't herpes." They are. Cold sores are caused by the herpes simplex virus. The stigma around the word "herpes" is way bigger than the reality of the virus — most of the population carries it.

"You can only pass it on when you can see a sore." The risk is much higher with a visible sore, but the virus can occasionally be passed on without one through asymptomatic shedding.

"If I've always had cold sores, it's fine to give oral sex." If you have an active cold sore, you can pass HSV-1 to someone's genitals. Waiting until the sore is fully healed significantly reduces the risk.

Things people ask about cold sores

If I get cold sores, does that mean I have an STI?

Cold sores are caused by the herpes virus, which is the same family of virus that causes genital herpes. Most people catch HSV-1 as children from non-sexual contact. Whether you call it an STI depends on how it was transmitted — but the virus itself is the same.

Can I get rid of the virus?

No. Once you have HSV-1, it stays in your body for life. But for most people it's a minor inconvenience at worst — occasional cold sores that heal on their own.

Should I tell a partner I get cold sores?

If you're about to give oral sex and you have (or recently had) a cold sore, yes — it's the right thing to do so they can make an informed decision. Given how common cold sores are, most people won't be fazed.

Where to get help

• Your pharmacist — for over-the-counter antiviral cream (aciclovir) to treat cold sores.
• Your GP — if you get cold sores very frequently, they can prescribe antiviral tablets.
• Sexual health clinics — for advice if you're worried about passing HSV-1 to a partner.

A cold sore is a small blister that pops up on or around your lips. It's caused by a virus called herpes simplex. Most people catch this virus when they're young, usually from being kissed by a family member. It's extremely common.

Once you have the virus, it stays in your body forever. Most of the time it does nothing. But sometimes — when you're stressed, tired, or ill — it can wake up and cause a cold sore. The sore usually tingles first, then turns into a blister, then crusts over and heals in a week or two.

The reason cold sores come up in sex education is that the virus can be spread to someone's private parts through oral sex. If you have a cold sore and give oral sex, you can give your partner the same virus in a different place on their body.

The easiest way to stop this happening is to avoid kissing and oral sex when you have a cold sore. Wait until it's fully healed.

Cream from the pharmacy can help cold sores heal faster if you put it on early, when you first feel the tingle.