Skip to main content

Health condition · Clinically reviewed

Cold sores, the tingle, the antiviral and when to escalate.

Recurrent HSV on the lip is common and mostly self-limiting. Early antivirals shorten attacks, and a few clear red flags need same-day medical care.

Jump to treatment
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE CKS, BASHH and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK guidance on antivirals, when to escalate and the ocular red flags.

Key facts

Cold sores at a glance.

The essentials, in plain English - what a cold sore is, what triggers it and how it is treated in the UK today.

  • What it is

    Recurrent HSV-1 (mostly) or HSV-2 orolabial infection - tingling, then grouped vesicles, ulcers and crusts healing over 7 to 10 days.

  • How common

    Very common - most UK adults carry HSV-1, though not everyone gets visible cold sores.

  • First infection

    Often silent in childhood - sometimes a florid gingivostomatitis with fever, mouth ulcers and swollen glands.

  • Triggers

    Sun and UV, colds and fever, stress, tiredness, menstruation, trauma to the lip and lowered immunity.

  • Foundation care

    Most episodes are self-limiting - sun protection, hygiene and topical aciclovir at the tingle stage help.

  • When to escalate

    Frequent, severe, immunocompromised, near the eye, in atopic eczema or in neonates - all need medical review.

Why this guide matters

A quick plan, and a short list of red flags.

Cold sores are common and mostly manageable at home. The three points below shape everything else on this page.

  • Early antivirals help most

    The best time to act is the tingle stage - topical or oral aciclovir, valaciclovir or famciclovir start working before the blister forms.

  • Sun is the trigger to manage

    Daily SPF lip balm reduces recurrence more than almost any other single habit.

  • Some cold sores are emergencies

    Eye involvement, eczema herpeticum, neonates and encephalitis need same-day hospital care - the rest of this page shows when.

How the diagnosis is made

From tingle to a clear plan.

The steps a UK GP will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History of prodrome

    A day of tingling, burning or itching on the same spot before the blister appears is highly suggestive of HSV.

  2. 02

    Assessing

    Look at the lesion

    Grouped vesicles on an erythematous base at the vermillion border of the lip is the classic cold sore pattern.

  3. 03

    Assessing

    Site check - mouth or lip?

    Cold sores sit on the lip, chin or nose. Ulcers on non-keratinised mouth lining are usually canker sores (aphthous), not HSV.

  4. 04

    Confirming

    Swab for PCR when uncertain

    A vesicle-fluid swab sent for HSV PCR distinguishes HSV-1 from HSV-2 and confirms diagnosis in immunocompromised or severe cases.

  5. 05

    Confirming

    Exclude look-alikes

    Impetigo, contact dermatitis and early shingles (VZV) can mimic HSV - a careful look and, if needed, swab settles it.

  6. 06

    Preparing

    Ophthalmology if eye involved

    Any red eye, pain, blurred vision or lesions near the eye needs same-day ophthalmology - HSV keratitis is sight-threatening.

  7. 07

    Preparing

    Plan for frequent recurrences

    More than six episodes a year, disabling attacks or post-HSV erythema multiforme are triggers for daily suppressive antiviral therapy.

Typical timeline: from first tingle to healed skin in 7 to 10 days.

Symptoms

What a cold sore actually looks like.

The classic stages, and the features that mean it is time to see someone urgently.

  • Prodrome

    Tingling, burning or itching at the site 12 to 24 hours before any visible change - the best moment to start topical antiviral.

  • Erythema and papules

    A small red patch appears and firms up into tiny bumps within hours.

  • Grouped vesicles

    Clusters of clear fluid-filled blisters on a red base - the hallmark of HSV.

  • Pustules and ulceration

    Blisters cloud, burst and leave shallow ulcers - often painful for a day or two.

  • Crusting and healing

    Golden crusts form and separate over 7 to 10 days - scarring is unusual with normal healing.

  • Same-site recurrence

    Attacks tend to return to the same lip corner, chin or nostril each time.

  • Systemic first episode

    A first infection in children can be florid - fever, extensive mouth ulcers and swollen neck glands (gingivostomatitis).

  • Red flag - eye involvement

    Lesions near the eye, a red painful eye or blurred vision need urgent ophthalmology - avoid topical steroid.

Treatment

How cold sores are treated in the UK.

Supportive care first, topical or oral antiviral started at the tingle stage, and daily suppression for frequent or severe recurrences.

  • Supportive care

    Cool compresses, bland lip balm, gentle cleaning and no picking - most episodes settle in a week or two on their own.

  • Sun and trigger avoidance

    SPF lip balm, hats and managing stress, sleep and colds reduce how often cold sores return.

  • Topical aciclovir 5% cream

    Applied five times a day for five days - modest benefit, best if started at the tingle stage.

  • Topical penciclovir or docosanol

    Alternative over-the-counter creams - similar modest benefit when applied early and often.

  • Oral aciclovir

    200 to 400 mg five times a day or 800 mg three times a day for five days - for severe or frequent episodes.

  • Oral valaciclovir (Valtrex)

    High-dose short course - 2 g twice for one day - is a convenient option started at prodrome.

  • Oral famciclovir

    1500 mg as a single dose or 500 mg twice for one day - another short-course oral option.

  • Daily suppressive antiviral

    Aciclovir 400 mg twice daily or valaciclovir 500 mg daily for frequent, severe or complication-prone recurrences.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or pharmacist can tell you which of these steps applies to you. If in doubt - especially with an eye or an unwell baby - get seen the same day.

  • NICE Clinical Knowledge Summaries. Herpes simplex - oral.

  • BASHH. UK national guideline on the management of anogenital herpes (background HSV pharmacology).

  • MHRA and BNF. Aciclovir, valaciclovir and famciclovir prescribing information.

  • Royal College of Ophthalmologists. Herpes simplex keratitis clinical guidance.

Red flags

When a cold sore needs urgent attention.

Most attacks settle at home. These are the situations that need same-day medical care.

  • Herpetic eye disease

    Lesions near the eye, a red painful eye, watering or blurred vision suggest HSV keratitis - same-day ophthalmology and no topical steroid.

  • Eczema herpeticum

    HSV superinfecting atopic eczema causes widespread painful clusters, systemic upset and needs urgent assessment for IV aciclovir.

  • Neonatal herpes

    A blistering rash, feeding trouble or unwell baby with any maternal HSV history is an emergency - admit for IV antiviral therapy.

  • Herpes encephalitis

    Fever, confusion, seizures or focal neurology - a rare but serious HSV complication needing hospital admission and IV aciclovir.

  • Herpetic whitlow

    A painful blistering finger lesion, often in healthcare workers or children - HSV, not bacterial - manage with oral antiviral, avoid incision.

  • Herpes gladiatorum

    Wrestlers and rugby forwards can develop HSV skin outbreaks - keep off the mat until crusted and treat with oral antiviral.

  • Immunocompromised patient

    Disseminated, prolonged or atypical HSV needs prompt swab, oral or IV antiviral and specialist input.

  • Recurrent erythema multiforme

    Target-lesion rashes triggered by HSV are a strong indication for daily suppressive antiviral therapy.

  • Very frequent recurrences

    More than six attacks a year, or attacks that disrupt work, sleep or mood, deserve a suppression conversation with a GP.

Living with it

A treatable pattern, with a clear ladder.

Four things that make the biggest difference day to day - acting early, protecting your lips from UV, keeping vulnerable people safe and knowing when to ask about daily suppression.

A quiet reminder

Speed matters more than product.

Whichever antiviral you use, it works best in the first few hours - keep a tube where you will actually reach for it.

  1. 01 Early

    Treat at the tingle

    Antivirals - topical or oral - work best when started in the first hours of the prodrome, before blisters form.

  2. 02 Protect

    SPF lip balm, every day

    UV is a major trigger - a daily SPF lip balm and a hat in strong sun cut recurrences noticeably.

  3. 03 Consider

    Protect the vulnerable

    Avoid kissing infants, people with severe eczema and immunocompromised contacts while a cold sore is active.

  4. 04 Escalate

    Ask about suppression

    Frequent, disabling or complication-prone attacks respond well to daily antiviral therapy - it is safe long-term.

Frequently asked

Everything we get asked about cold sores.

Quick answers on antivirals, triggers, suppression and when a cold sore is an emergency.

  • What actually causes a cold sore?

    Reactivation of herpes simplex virus - usually HSV-1, occasionally HSV-2 - that has been living quietly in the trigeminal nerve since a first, often silent, childhood infection. Triggers such as UV, colds, stress or tiredness let the virus travel back down the nerve to the lip.

  • How long does a cold sore last?

    A typical episode runs seven to ten days from prodrome to fully healed. It moves through tingling, redness, blisters, ulcers, crusting and healing, and antivirals started early can shorten each stage a little.

  • When should I use aciclovir cream versus tablets?

    Topical aciclovir 5% cream, applied five times a day for five days from the tingle stage, is enough for most people with occasional mild cold sores. Oral aciclovir, valaciclovir or famciclovir is better for severe, frequent or complicated attacks and for anyone immunocompromised.

  • Can I stop the cold sores coming back?

    Sometimes yes. Daily suppressive antiviral therapy - typically aciclovir 400 mg twice daily or valaciclovir 500 mg daily - cuts the number of recurrences significantly and is used for people with more than six episodes a year, severe attacks or post-HSV erythema multiforme.

  • How do I tell a cold sore from a mouth ulcer?

    Cold sores sit on the lip, chin or nose - the keratinised outer skin - and start with grouped vesicles on a red base. Canker sores (aphthous ulcers) sit inside the mouth on the softer non-keratinised lining, are single or few, and never blister. If you are unsure, ask a GP.

  • When is a cold sore an emergency?

    Any lesion near or on the eye, sudden widespread blistering in someone with eczema, a very unwell newborn with blisters, or confusion and seizures with a rash all need urgent medical review the same day. Cold sores in the immunocompromised also need prompt input.

Related content

Keep reading.

Pulse Healthcare concierge

Send us your enquiry

A concierge service for UK private healthcare. We match you with the best vetted clinics and consultants in our network - they then contact you directly.

So we can match you to the right clinician close to you.

We reply to every enquiry within 24 hours (Mon–Fri). Confidential - your details are never shared outside our vetted consultant network.