Quick answer
What is cold sores?
Cold sores are small blisters on or around the lips caused by herpes simplex virus (usually HSV-1) — tingling often precedes the blister. They heal in 7 to 10 days but the virus stays in the body and can recur. Highly contagious when blisters are present — avoid kissing and oral sex until healed. Antiviral cream started early shortens outbreaks; tablets for frequent recurrences.
Cold sores — oral herpes simplex
Cold sores ( herpes labialis ) are fluid-filled blisters on or around the lips and mouth, caused by herpes simplex virus (HSV) — almost always HSV-1.
Roughly two-thirds of UK adults carry HSV-1; not all develop visible cold sores. Once infected, the virus remains for life in sensory nerves — reactivating as cold sores during triggers.
Symptoms
Recurrent cold sore (typical)
- Prodrome — tingling, burning, itching, tightness on lip — 12 to 36 hours before blister
- Blister cluster — painful, red base
- Weeping then crusting — heals 7 to 10 days
Primary infection (first time — often childhood)
May cause:
- gums and mouth ulcers
- sore throat
- swollen neck glands
- fever — can mimic glandular fever
Often more severe than recurrences.
Triggers for recurrence
- UV light — sun, sunbeds — use SPF lip balm
- stress and fatigue
- colds and fever
- menstruation
- skin injury around lips
Contagiousness
Spread by direct contact:
- kissing
- sharing lip balm, cups, towels
- oral sex — transmits to partner’s genitals (genital herpes)
Most infectious when blister is open; avoid contact until fully healed.
Neonatal risk: never kiss a newborn with active cold sore — rare neonatal HSV is devastating.
Treatment
Topical antivirals (pharmacy/GP)
Aciclovir 5% cream or penciclovir cream:
- apply at first tingle — 5 times daily for 5 days
- modest benefit if started early — shortens by ~1 day
Oral antivirals (GP)
Aciclovir, valaciclovir, famciclovir tablets for:
- severe primary infection
- frequent recurrences (≥6/year) — suppressive daily dose
- ** immunocompromised** patients
See aciclovir and antivirals guide.
Self-care
- do not pick — spreads virus, risks bacterial infection
- cold compress for comfort
- paracetamol/ibuprofen
- keep lips moisturised after crusting phase
Cold sores vs other lip problems
| Condition | Clues |
|---|---|
| Impetigo | Honey-crusted, bacterial, spreads fast |
| Angular cheilitis | Corners of mouth — fungal/bacterial |
| Aphthous ulcers | Inside mouth — not HSV typically on lips |
| Shingles | Unilateral dermatomal — see shingles |
Eye involvement — emergency
HSV keratitis — infection of cornea:
- red painful eye, light sensitivity, blurred vision
Same-day ophthalmology — prevents scarring and vision loss.
Prevention of recurrences
- sun protection on lips
- stress management
- suppressiv e oral antivirals if frequent
- avoid known triggers where possible
Cold sores are common, benign for most, but contagious and recurrent — early antiviral cream and trigger awareness reduce hassle and transmission.
Common questions
- What causes cold sores?
- Herpes simplex virus type 1 (HSV-1) in most cases — stays dormant in nerve cells after first infection, reactivates causing blisters. HSV-2 can also affect the mouth. First infection may be severe with sore throat and swollen glands; recurrences are usually milder lip blisters only.
- How do you get rid of a cold sore fast?
- Start aciclovir or penciclovir cream at the tingling stage — 5 times daily for 5 days — may shorten outbreak by 1 to 2 days. Keep area clean, avoid picking, use SPF lip balm to prevent sun-triggered recurrences. Oral antiviral tablets work better for severe or frequent outbreaks — GP prescription.
- Are cold sores contagious?
- Yes — most contagious when blister fluid is present; virus also sheds at low levels before and after visible sores. Avoid kissing, sharing lip products, towels, and oral sex until fully healed. Do not kiss babies if you have an active cold sore — neonatal herpes is rare but serious.
- Can cold sores spread to genitals?
- Yes — HSV-1 from oral cold sores causes a growing proportion of genital herpes infections through oral sex. Condoms reduce but do not eliminate oral-genital transmission. See our genital herpes guide if genital symptoms develop.
- Why do I keep getting cold sores?
- Triggers include UV light (sun, sunbeds), stress, fatigue, illness, fever, hormonal changes, and skin trauma. Frequent recurrences — 6 or more yearly — may justify daily suppressive aciclovir from GP.
- Is there a vaccine for cold sores?
- No licensed vaccine currently. Antivirals manage symptoms; research continues.