Cold sores

Also called Herpes simplex, Fever blisters

Caused by a virus most adults already carry. Harmless in most people, and genuinely dangerous around newborns and eczema.

What it is

Blisters around the lips and mouth caused by herpes simplex virus, usually type 1. Most people are infected in childhood, often by an adult's kiss, and around two thirds of adults carry it.

After the first infection the virus stays in a nerve near the spine for life and reactivates from time to time, triggered by illness, fever, sunlight, stress, tiredness or menstruation. Most people have a few episodes a year; some have none.

For almost everybody it is a nuisance. Three situations turn it into something serious, and they are the reason this entry is here.

**A newborn baby.** Neonatal herpes is rare and can be life-threatening. Nobody with an active cold sore should kiss a baby under three months, and any unwell newborn with blisters needs immediate assessment.

**Eczema.** The virus can spread across broken eczematous skin, called eczema herpeticum, causing rapidly worsening, painful, punched-out sores with fever. It is a medical emergency. See eczema.

**A weakened immune system**, where it can spread and needs antiviral treatment.

It can also infect the eye, causing pain, redness and light sensitivity, which needs same-day eye assessment and must never be treated with steroid drops.

Signs you might notice

A tingling, itching or burning feeling on the lip a day or so before anything appears. This is the moment treatment works best.

Small fluid-filled blisters, usually at the border of the lip, which burst, weep and crust over.

Healing within about 10 days without scarring.

A first infection in a child can be much worse: painful mouth ulcers throughout the mouth, fever, swollen glands and difficulty eating and drinking.

999 or urgent: a baby under three months with blisters, fever, poor feeding or floppiness; rapidly spreading painful sores on eczema with fever; a red painful eye with light sensitivity.

How it can affect day-to-day life

The stigma is disproportionate to the biology. Most adults carry the virus, and having a visible sore says nothing about anybody's behaviour.

For people who get frequent recurrences, the visible sore affects work, confidence and relationships more than the symptoms do, and suppressive antiviral treatment is available and rarely offered.

In care settings, staff with active cold sores should not provide mouth care or work with newborns, and should cover the sore and wash hands scrupulously.

Sunlight is a common trigger; lip balm with a sun protection factor genuinely reduces recurrences for those people.

Supporting someone well

Treat at the tingle. Antiviral cream works if started before the blister forms and barely at all afterwards. Keep some in.

Do not kiss babies, and do not let anyone with a cold sore near a newborn's face.

Do not touch the sore then the eyes, and wash hands after applying anything.

Do not share towels, cutlery, lip balm or razors while a sore is active.

For anybody with eczema, watch for rapidly spreading painful sores and treat that as an emergency.

For frequent recurrences, ask about suppressive antiviral tablets.

Use a sun-protective lip balm if sunlight is a trigger.

Never use steroid eye drops for a red eye without an eye assessment.

Where to get help

A pharmacist for antiviral cream and advice, including through Pharmacy First.

A GP practice for frequent recurrences, a first severe episode, or anybody immunosuppressed.

Same-day: a baby with blisters, spreading sores on eczema, or a painful red eye.

Herpes Viruses Association provide accurate information and a helpline.