Condition

Cold Sores (Herpes Labialis)

Cold sores are painful blisters on or around the lip, caused by the herpes simplex virus. They are contagious, they come back, and treatment works best if you start it at the first tingle.
At a Glance

Cold sores are small painful blisters on or around the lip, caused by herpes simplex virus type 1 — a virus most adults carry and that stays in the body for life. Unlike most of the harmless bumps people look up, this one is genuinely contagious, especially while the blister is open, and it is genuinely treatable. Timing is the whole game: antiviral tablets started within the first hours, at the tingling stage, can cut an outbreak short, and once the blister has crusted they barely help at all. That is why it is worth keeping a prescription at home rather than trying to get one after the sore appears.

Key Facts

How CommonVery common. Around two thirds of people under 50 worldwide carry the virus, though most never get visible sores.
Who Gets ItAnyone carrying HSV-1. Most people catch it in childhood, from a kiss by an adult who had no sore at the time.
Chronic or CurableChronic. The virus stays in a nerve for life. Outbreaks are treatable and often become less frequent with age, but there is no cure.
Rx RequiredAntiviral tablets need a prescription. Over-the-counter creams and patches do not.
ContagiousYes. Most contagious from the tingle through to the crust, but the virus can be passed on with no sore present at all.
CostGeneric antiviral tablets are inexpensive. Some branded creams cost far more than they are worth.

Symptoms

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Cold sores follow the same sequence nearly every time, and knowing that sequence is what lets you treat one early enough to matter.

What it looks and feels like

The tingle first — burning, itching, tightness or a prickly feeling in one spot, usually 6 to 24 hours before anything is visible. This is the window where treatment works best.
A red, swollen patch — the area becomes tender and slightly puffy.
A cluster of small blisters — several tiny fluid-filled blisters grouped together on a red base, not one single blister. The grouping is the identifying feature.
Blisters break and weep — they burst within a day or two into a shallow, raw, painful sore. This is the most contagious stage.
A yellow-brown crust — the sore scabs over for several days, and cracks and bleeds if the lip is stretched.
Swollen glands and feeling unwell — mainly with a first-ever infection, which is usually much worse than later ones and can include fever, sore throat and sores inside the mouth.

Where it shows up

  • The border of the lip, where lip meets skin, is by far the most common spot.
  • Around the mouth, the nostrils and the chin.
  • The same place nearly every time, because the virus travels back down the same nerve.
  • Inside the mouth, but essentially only during a first infection in a child. Recurring sores inside the mouth are almost always canker sores, which are a completely different thing.
  • A finger, if the virus gets into broken skin around a nail.

How it looks on different skin tones

The blisters look the same on all skin tones — small, clear or cloudy fluid-filled bumps that crust over yellow-brown. The red base is easier to see on light skin. On brown and Black skin the surrounding skin may look darker, purplish or ashy rather than red, so the swelling and the grouped blisters are the more reliable clues. Once healed, the spot often leaves a darker mark for weeks to months, which is pigment change rather than a scar.

Light
Medium
Brown
Deep

Several mouth and lip problems get called cold sores. See Lookalikes near the bottom of this page.

Causes & Risk Factors

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Cold sores are caused by herpes simplex virus, nearly always type 1. Most people catch it as a young child, usually from an ordinary kiss from an adult who had no sore visible at the time. That first infection often causes nothing noticeable, or a bout of sore, ulcerated gums and fever that gets put down to teething.

After that, the virus does not leave. It travels up a nerve and settles in a cluster of nerve cells near the base of the skull, where it sits inactive and out of reach of the immune system. From time to time it reactivates, travels back down the same nerve, and produces a sore in roughly the same place. Nobody fully knows why it reactivates when it does, but the triggers are consistent: strong sunlight on the lips, fever and illness, physical or emotional stress, exhaustion, dental work or lip injury, and for some women the days around a period. Having cold sores says nothing about hygiene or about your sex life — most people carrying this virus got it before they started school. Only about a quarter to a third of carriers ever get visible sores at all, and why some do and most do not comes down largely to genetics.

What Hurts and What Helps

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What Makes It Worse

  • Sunlight on the lips. This is the most reliable trigger of all, and the one you can actually do something about. Ski trips and beach holidays set off outbreaks in a lot of people.
  • Being ill or running a fever. The old name for these was fever blisters for a reason.
  • Stress, exhaustion and poor sleep.
  • Dental work, lip injury, cosmetic lip procedures, and even aggressive lip scrubbing.
  • Hormonal shifts, including the days before a period.
  • Picking the scab. It reopens the sore, delays healing by days, puts virus on your fingers, and is the main reason a cold sore leaves a mark.
  • Waiting to start treatment. Antivirals lose most of their benefit once the blister has formed, and are close to useless once it has crusted.

Daily Habits That Help

  • Starting antiviral treatment at the tingle. This is the single most effective thing on this page. Have the tablets at home already, so the first dose is within hours rather than after two days of trying to get an appointment.
  • Lip balm with sunscreen, used daily. There is real trial evidence that SPF on the lips prevents sun-triggered outbreaks, and it costs almost nothing.
  • Keeping the sore covered and moist. Petroleum jelly or a hydrocolloid patch stops the crust cracking and reduces the chance of spreading it.
  • A cold compress for ten minutes, which genuinely helps the pain and swelling.
  • Not touching it, and washing your hands if you do. Virus carried on a finger to your eye is the one thing on this page that really matters.
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  • Suppressive dosing, if you get frequent outbreaks. A low daily dose of an antiviral taken continuously cuts the number of outbreaks substantially. It is a normal, well-established option rather than a last resort.
  • Skipping kissing, oral sex, and shared cups, cutlery, towels and lip balm from the tingle until the sore has fully healed.

Try at Home

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These help with comfort and can shorten an outbreak slightly. None of them come close to what an antiviral tablet started at the tingle does, so treat them as support rather than as the treatment.

Always
Sunlight on the lips is the most reliable trigger there is, and this is the one prevention step with real trial evidence behind it. Use it daily, and reapply on ski trips and beach days.
Always
Keeps the crust soft so it does not split and bleed every time you talk or eat. It does not shorten the outbreak, but it makes days five to ten considerably more comfortable. Use a clean finger or a cotton bud, not the tube on your lip.
Always
A thin gel patch worn over the sore. It covers it, keeps it moist, reduces the urge to pick, and contains the fluid — which matters, because that fluid is how you pass it on and how it reaches your own eye.
Moderate evidence
The main over-the-counter antiviral cream. Started at the tingle and applied five times a day, it shortens an outbreak by roughly half a day on average. That is a real effect, and a small one compared with tablets.
Moderate evidence
Purely for pain. It numbs the sore for an hour or two, which helps with eating and sleeping during the worst days. It does nothing to the virus and does not shorten anything.
Limited evidence
A few small studies of zinc oxide with glycine suggest it shortens an outbreak slightly when started early. It is cheap and safe, but the evidence behind it is much thinner than for antivirals.
Limited evidence
One of the most popular remedies for cold sores, and one of the least well supported. Some small trials suggest fewer outbreaks at higher daily doses; others show nothing. Cheap and safe to try, but not a substitute for an antiviral.

When to See a Dermatologist

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Most cold sores are managed at home once you have a prescription in the cupboard. Worth booking if:

  • You have never had one before and want the diagnosis confirmed, plus a prescription for next time.
  • You get them more than a few times a year. Daily suppressive dosing is worth discussing.
  • Outbreaks are severe, last more than two weeks, or are spreading beyond the usual spot.
  • You want tablets on hand before a trip, a wedding, dental work or a lip treatment.

Get care the same day, not an appointment in a fortnight, if:

  • The eye is involved. Pain, redness, watering, light sensitivity or blurred vision, or a sore near the eye. Herpes in the eye can damage sight and needs treating immediately.
  • Sores are spreading across skin that has eczema. Clusters of painful punched-out sores spreading over eczema, often with fever, is called eczema herpeticum and needs urgent antiviral treatment.
  • The person has a suppressed immune system — from chemotherapy, transplant medication, high-dose steroids or advanced HIV — and the sore is spreading or not healing.
  • A newborn has been exposed. Herpes in the first weeks of life is a medical emergency. Do not kiss a newborn if you have an active cold sore, and tell the parents if you do.
What Happens at the Dermatologist?+

A typical cold sore in someone who has had them before does not need any test. It is recognised from the grouped blisters, the location, and the fact that it keeps returning to the same spot.

A test is done when the answer would change something.

  • A viral swab with PCR. The sore is swabbed, ideally while the blister is fresh and still fluid-filled, and the sample checked for herpes DNA. This is the accurate test, and it also says whether it is type 1 or type 2. Worth doing for a first outbreak, for an unusual-looking sore, when a sore is not healing, and in anyone whose immune system is suppressed. Swabbing a dry crust often gives a false negative, so timing matters.
  • A blood test for herpes antibodies. This tells you whether you have ever been exposed to the virus, not whether the sore on your lip today is herpes. Because most adults are positive, it usually answers a question nobody asked. It has real uses, mostly around pregnancy and partner testing, but it is not the test for diagnosing a cold sore.
  • A bacterial swab. Taken when a sore is unusually crusted, spreading or golden-yellow, to check for impetigo or a bacterial infection sitting on top of the cold sore.

The old Tzanck smear, where cells from the blister are looked at under a microscope, is rarely used now. PCR replaced it and is far more accurate.

Prescription Treatments

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This is what actually shortens a cold sore, and only if you start early. Tablets work considerably better than creams. If you get outbreaks regularly, ask for a supply to keep at home so you can start within hours instead of days.

Topical prescriptions
Moderate evidence
A prescription antiviral cream applied every two hours while awake. It shortens an outbreak by around a day when started at the tingle. Effective, but the dosing is demanding and tablets do more.
Topical prescriptions
Limited evidence
Honestly, the weakest of the prescription options. Acyclovir does not absorb well through lip skin, and trials show it shortens an outbreak by well under a day. If you can take tablets instead, take the tablets.
Pills and injections
Valacyclovir (Valtrex)
Strong evidence
The most convenient option and the one most people are given. Two large doses taken twelve hours apart, started at the tingle, can cut an outbreak short or stop it appearing. It can also be taken daily to prevent frequent outbreaks. Keep a supply at home so you are not waiting for an appointment.
Pills and injections
Strong evidence
The original antiviral, and very cheap. It works well, but it has to be taken five times a day for five days, which is why most people are given valacyclovir instead. Same rule applies: start at the tingle.
Pills and injections
Strong evidence
Another single-day option — one large dose taken at the first tingle. It works as well as valacyclovir, and which one you get usually comes down to cost and what your pharmacy stocks.

What to Expect

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Step 1
The first 24 hours

The tingle comes before anything visible. This is the window where an antiviral tablet makes the biggest difference. It can knock an outbreak back by a day or two, and occasionally stop it appearing at all.

Step 2
Days 2 to 4

Blisters form, break and weep. This is the painful stage and the most contagious one. Antivirals started now help a little. Started after this, they help very little.

Step 3
Days 5 to 8

The sore crusts over. It looks worse than it feels by this point. Petroleum jelly over the crust stops it splitting.

Step 4
Days 8 to 14

The crust separates and the skin underneath heals. An untreated outbreak usually runs 7 to 14 days start to finish. A treated one is typically a day or two shorter.

Step 5
How often it comes back

Most people who get recurrences have a few a year, and the same trigger tends to set them off each time. Outbreaks generally become less frequent with age.

Step 6
The honest long view

There is no cure and nothing clears the virus from your body. What is achievable is shorter outbreaks, fewer of them, and much lower risk of passing it on — and the difference between managing this well and badly is almost entirely about starting early and having the medication before you need it.

Complications

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For most healthy people a cold sore is painful and inconvenient and nothing more. A few complications matter, and they are worth knowing about without being alarmed by.

  • Spread to the eye (herpes keratitis). Virus carried on a finger to the eye can infect the cornea. Eye pain, redness, watering, light sensitivity or blurred vision alongside a cold sore needs same-day care, because repeated episodes can scar the cornea and damage sight. This is the reason for not touching the sore.
  • Eczema herpeticum. If the virus lands on eczema-damaged skin it can spread widely, causing clusters of small punched-out sores with fever and feeling unwell. It needs urgent antiviral treatment. Anyone with eczema should keep away from an active cold sore.
  • Bacterial infection on top. Golden-yellow crusting, increasing pain, swelling and spreading redness suggest impetigo has set in over the sore, which needs an antibiotic.
  • Herpetic whitlow. A painful cluster of blisters on a finger, from the virus getting into broken skin around a nail. Common in children who suck a thumb during an outbreak.
  • Serious infection in a newborn. Herpes in a baby in the first weeks of life can be severe. Do not kiss a newborn if you have an active or developing sore.
  • Severe or persistent outbreaks in a suppressed immune system. Sores that are larger, deeper, slower to heal or spreading need medical treatment rather than waiting.
  • Marks left behind. Darker patches where the sore was are common and fade over weeks to months. Scars are uncommon and usually follow repeated picking.

Lookalikes

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Several different things turn up on and around the mouth, and they are treated in completely different ways.

  • Canker sores (aphthous ulcers). The most common mix-up by a distance. Canker sores are round or oval white or yellow ulcers with a red rim, and they are inside the mouth — on the inner lip, cheek, tongue or under the tongue. They are not herpes, they are not contagious, and antivirals do nothing for them. Cold sores are on the outside of the lip and start as a cluster of blisters.
  • Angular cheilitis. Cracked, sore, red or crusted corners of the mouth, usually on both sides at once, that keeps coming back. It is irritation with yeast or bacteria on top, not a virus, and it is treated with an antifungal or antibacterial cream. Cold sores rarely sit exactly in the corner and rarely appear on both sides.
  • Impetigo. A bacterial infection with honey-coloured golden crusting that spreads outward across the skin, common in children. It usually itches more than it hurts. Needs an antibiotic, not an antiviral.
  • Chapped, split lips. Dry, cracked lips with no blisters and no tingle beforehand. Painful, but it does not follow the blister-to-crust sequence.
  • Perioral dermatitis. A rash of small red bumps and pustules around the mouth, often sparing a thin border right at the lip line, lasting weeks rather than days. Often triggered by steroid creams.
  • Shingles. A painful blistering rash following a nerve on one side of the face, stopping sharply at the midline, and usually covering a much larger area than a cold sore.
  • Mucocele. A soft, clear, painless bubble on the inner lip from a blocked saliva gland, usually after biting the lip.
FAQ+
When should I start treatment?At the tingle, before you can see anything. Antivirals work by stopping the virus multiplying, so once the blister has formed most of the damage is already done, and once it has crusted they do almost nothing. The practical advice is to get a prescription in advance and keep it at home.
Are cold sores a sexually transmitted infection?Not usually. Most people catch HSV-1 in childhood from a kiss from a relative. But the virus can be passed to a partner's genitals through oral sex, so it is worth avoiding that during an outbreak.
How long am I contagious?From the tingle until the sore has completely healed and the skin is back to normal, which is typically one to two weeks. The weeping blister stage is the most contagious. The virus can also be shed with no sore visible at all, which is how most people catch it in the first place.
Can I kiss my baby?Not with an active or developing cold sore. Herpes in a newborn can be very serious. Wait until the sore is fully healed, and wash your hands carefully.
Does Abreva work?A little. Docosanol shortens an outbreak by roughly half a day on average when started very early. That is a real effect but a small one, and much less than antiviral tablets do.
Does lysine help?The evidence is weak and inconsistent. Some small trials suggest fewer outbreaks at higher doses, others show nothing. It is cheap and generally safe, so trying it is reasonable, but it should not replace an antiviral.
What is the difference between a cold sore and a canker sore?A canker sore is an ulcer inside the mouth, is not caused by herpes, and is not contagious. A cold sore is a cluster of blisters on the outside of the lip caused by herpes simplex. This confusion is extremely common, and it matters because antivirals do nothing for canker sores.
Can I get rid of the virus for good?No. It lives permanently in a nerve. Treatment shortens outbreaks and reduces how often they happen, but nothing available clears it.
What is suppressive treatment?A low dose of an antiviral taken every day rather than only during an outbreak. It substantially reduces how often outbreaks happen and how much virus you shed. It is a normal option for anyone getting frequent sores.
Why do I always get one in the same spot?Because the virus lives in one nerve and travels back down the same path each time.
Do cold sores scar?Rarely. What usually stays is a darker or lighter mark that fades over weeks to months. Repeated picking is the main cause of an actual scar.
Do I need to tell a partner?It is fair to. Cold sores are extremely common and most adults already carry the virus, but the risk of passing it on is real during an outbreak, and it is higher through oral sex than most people expect.