Condition

Cold Sores

Cold sores are small clusters of blisters on or around the lip, caused by the herpes simplex virus. The virus stays in the body for life, but episodes get shorter when treatment starts early, and for most people they become less frequent over the years.
Dr. Schwarz, MD · Board-certified dermatologistLast reviewed September 8, 2026
16:9 hero for Cold Sores. Never cropped: the tone strip and the corner logo depend on the full frame.

Start here

Most people who get cold sores caught the virus as a small child, usually from an ordinary kiss, so it says nothing about you - it is one of the commonest infections in the world. Almost everyone waits for a visible blister before doing anything, and by then the virus has finished most of its multiplying. Learn your own warning sign - the tingle, itch or tight feeling that shows up a day early - and treat at that moment, which is why I like patients to keep a course of antiviral tablets in a drawer instead of chasing an appointment on the morning it starts. Episodes also get less frequent with age - patients who came to me in their twenties with one a month are often down to a couple a year by their forties.

— Dr. Schwarz, Board Certified Dermatologist

Key Facts

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How commonVery common - roughly two thirds of people under 50 worldwide carry the virus, though only some of them ever get visible sores
Who gets itMost people catch the virus in childhood. Sores can start at any age
Curable or managedManaged - the virus stays in the body for life, but episodes can be shortened and prevented
Prescription neededNot always. Over-the-counter cream helps a little; prescription antiviral tablets help more
Time to improveAbout 7 to 10 days on its own, a day or two less if antivirals start at the first tingle

What It Is

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A cold sore is a tight cluster of small blisters on or just outside the lip border, caused by herpes simplex virus, almost always type 1. The blisters break within a day or two, leave a shallow raw patch, then crust and heal.

The first infection usually happens in early childhood and often causes nothing. In some children it causes a sore, swollen mouth and gums with fever, called gingivostomatitis - unpleasant for a week, then over. After that the virus does not leave. It travels up a sensory nerve to a cluster of nerve cell bodies behind the cheekbone, the trigeminal ganglion, and sits there inactive.

Now and then it reactivates, travels back down that nerve, and produces a sore in the same small patch of skin. That is why they keep appearing in the same place.

Cold sores are not canker sores. Canker sores are shallow ulcers on the soft lining inside the mouth, not viral and not contagious. Cold sores sit on the lip border or the skin around it.

Symptoms

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Before anything shows

Tingling Stage

A tingle, itch or burn on the lip a day or so before a blister appears. Nothing may be visible yet. This is the point where antiviral treatment works best, so recognizing it matters more than it looks.
Small clustered blisters

Blister and Weeping

A cluster of small blisters on or near the lip border that break open and weep. This is the most contagious stage, through kissing and shared items. Picking at them spreads the virus to other spots.
The scab stage

Crusted and Healing

The broken blisters dry into a yellow crust that cracks when the mouth moves. It usually settles over a week to ten days without a scar. Keeping the crust soft reduces splitting and bleeding.

Where It Shows Up

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Front view of a head with red marks along the upper and lower lip, at both corners of the mouth, at the base of the nose and on the chin.
The lip border, and the same patch every time
Almost always on the border of the lip or the skin just outside it, and usually the same small patch each time, because one nerve supplies one patch of skin. The corner of the mouth, the base of the nose and the chin are the next most common places. Rarely a sore turns up on a cheek, a finger or near an eye.

What Happens in the Skin

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This is what is going wrong under the skin, in the order it happens. Click a step to see it.

How Cold Sores happens
Skin basics
BARRIEREPIDERMISDERMISNERVE0A SLEEPING VIRUS1THE VIRUS WAKES UP2IT TRAVELS DOWN THE NERVE3BLISTERS FORM AND SHED VIRUS4IT HEALS AND GOES BACK TO SLEEP

After a first infection, herpes simplex retreats up a nerve and sits quietly in a nerve bundle near the spine or the base of the skull. Most of the time it does nothing at all.

Illness, fever, sunlight, stress, tiredness or a period can wake it. Many people feel a tingle or burn hours before anything shows.

The virus moves down the nerve fiber to the patch of skin that nerve serves - which is why cold sores come back in the same spot each time.

It multiplies in the skin cells there, raising a cluster of small blisters. This is the stage when it can be passed to someone else.

The blisters crust and heal within a week or two. The virus retreats up the nerve and waits - treatment shortens an attack but does not remove it.

The outer film of dead cells and oil. It holds water in and keeps irritants out, and it is thinner than a sheet of paper. Almost every dry, itchy, stinging skin problem starts here.

The outer layer, and the only one anything in a jar reaches. It renews itself constantly: a cell made at the bottom takes about a month to reach the surface and flake off. Most of what a skincare product does, it does here.

The living layer underneath, holding the blood vessels, the nerves and the collagen. It is where lasting change happens and it is hard to reach: most of what is sold for the skin never gets this far.

Four things happen, in order. The virus, sitting quietly in a nerve cluster near the cheekbone since childhood, is switched back on by something - strong sun, a fever, a bad night, hormonal shifts. It travels back down that sensory nerve to the small patch of lip it supplies, which takes a few hours and produces the tingling. It multiplies inside the skin cells there, and those cells swell and break apart, which is what a blister is. Then the immune system arrives in force, and the redness, swelling and soreness are that response, not the virus.

The nerve is why cold sores keep coming back to the same spot. Nothing you put on the skin reaches the virus while it is dormant there, so there is no cure - only treatment that shortens episodes and, if needed, daily medicine that prevents them.

Risk Factors

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Some people carry the virus for life and never get a sore; others get several a year. The difference is mostly out of your control.

The virus
Carrying HSV-1
The starting requirement. Most people caught it in childhood and never knew.
Everyday triggers
Strong sun on the lips
A consistent trigger. Skiing, beach holidays and long days outdoors set off episodes reliably.
Everyday triggers
Fever and illness
Where the old name fever blister comes from. Any illness with a temperature can bring one on.
Everyday triggers
Stress and short sleep
Both raise the chance of reactivation, especially over weeks rather than a day.
Everyday triggers
Lip injury
Dental work, a split lip, waxing, laser or aggressive exfoliation can all trigger the nerve.
Hormones
Menstrual cycle
Some people get an episode at the same point each month.
Other health conditions
A weakened immune system
Chemotherapy, transplant medicines, high-dose steroids and untreated HIV make episodes bigger and slower to heal. Ask your doctor.
Other health conditions
Eczema
Broken, inflamed skin lets the virus spread widely instead of staying in one spot.

Course

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Most episodes run a week to ten days. People settle into a rhythm - one or two a year, or several, and some have one episode and never another. Frequency drops with age.

WarningHours 6 to 24
The best moment to start treatment

Tingling, itching, burning or tightness in one small spot on the lip. Nothing visible yet.

One small spot on the lip
BlisteringDays 1 to 2
Often the most painful stage

A cluster of small, tense blisters on a red or swollen base.

OpenDays 2 to 4
The most contagious point of the episode

The blisters break, leaving a shallow, weeping raw patch.

CrustingDays 4 to 8
A yellow-brown crust forms and dries

It cracks when the lip moves, which is why it bleeds a little.

HealingDays 8 to 10
The mark fades over weeks

The crust comes away, leaving skin that is pink, or brown to gray on deeper skin tones. They heal without scarring unless picked repeatedly or infected with bacteria.

What Makes It Better & Worse

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A cold sore is four problems — waking up, multiplying, spreading, healing. What helps depends on where you are in the episode, and almost all the benefit of antivirals is on the first day.

What is driving yours?

FATNERVEBARRIEREPIDERMISDERMIS

Illness, fever, sunlight, stress, tiredness or a period can wake it. Many people feel a tingle or burn hours before anything shows.

The virus moves down the nerve fiber to the patch of skin that nerve serves - which is why cold sores come back in the same spot each time.

It multiplies in the skin cells there, raising a cluster of small blisters. This is the stage when it can be passed to someone else.

The blisters crust and heal within a week or two. The virus retreats up the nerve and waits - treatment shortens an attack but does not remove it.

What helps

  • A lip balm with SPF, used daily Prevention if your episodes follow sun.
  • Daily suppressive antiviral treatment For six or more episodes a year.

What makes it worse

  • Strong sun on the lips The most predictable trigger.
  • Being run down Fever, flu or a heavy cold keeps the immune system busy.
  • Stress and short sleep Both make reactivation more likely.
  • Injury to the lip Dental work, waxing, fillers, laser.

What helps

  • Treat at the first tingle Tablets in the warning stage shorten the episode.
  • Keep a course at home In a drawer, not at the end of a queue.
  • Docosanol cream, over the counter Shortens an episode modestly.

What makes it worse

  • Waiting for the blister before treating By then the multiplying is done.
  • Steroid cream on the lip Calms redness, lets the virus spread.

What helps

  • Hydrocolloid cold sore patches Cover the sore, keep it moist, reduce spread.
  • Hand washing and not sharing Worth it around newborns and anyone with eczema.

What makes it worse

  • Picking the crust Restarts healing and leaves a longer mark.
  • Touching the sore and then your eye Herpes simplex in the eye does real damage.
  • Sharing during an episode Lip balm, drinks, utensils, towels.
  • Kissing while a sore is open Especially near a newborn or anyone with eczema.

What helps

  • Leave the crust alone Picking slows healing.
  • Plain petrolatum ointment over the sore Keeps the crust from splitting.
  • A cold compress and ordinary pain relief For the first two days, when soreness peaks.

What makes it worse

  • Letting the area dry out and crack A split crust heals slower.

How These Treatments Work

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Treatments for Cold Sores do not all work in the same place. Tap one to see where it acts.

Pick a treatment
Skin basics
BARRIEREPIDERMISDERMISNERVESTOPS IT MULTIPLYINGKEEPS IT ASLEEPREMOVES A TRIGGEREASES THE SOREIT STAYS IN THE NERVE

Works only if started at the first tingle, before the blister forms.

For people getting frequent outbreaks. Taken every day rather than per sore.

Sun is one of the reliable things that wakes the virus.

Treats the symptom while the outbreak runs its course.

Treatment controls outbreaks. It does not remove the virus.

The outer film of dead cells and oil. It holds water in and keeps irritants out, and it is thinner than a sheet of paper. Almost every dry, itchy, stinging skin problem starts here.

The outer layer, and the only one anything in a jar reaches. It renews itself constantly: a cell made at the bottom takes about a month to reach the surface and flake off. Most of what a skincare product does, it does here.

The living layer underneath, holding the blood vessels, the nerves and the collagen. It is where lasting change happens and it is hard to reach: most of what is sold for the skin never gets this far.

Over-the-Counter Products

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Everything here you can buy without seeing anyone.

A white cream tube lying on its side on a white background, with a plain white label reading Docosanol and a yellow swoosh beneath it.
Abreva
Moderate evidence
The only over-the-counter cream shown to shorten an episode, and only by about half a day. It has to go on at the first tingle and be reapplied five times a day. It is a reasonable thing to keep in a bag, but antiviral tablets started at the same moment do considerably more.
Lip balm with SPF
Lip balm with SPF
Moderate evidence
Strong sun on the lips is one of the most reliable triggers there is, so for anyone whose episodes follow skiing, a beach holiday or long days outdoors, a daily SPF lip balm is genuine prevention rather than lip care. Use it every day rather than only when an episode is due, and keep using it while the mark left behind fades, since sun makes that darker and slower.
Hydrocolloid cold sore patches
Hydrocolloid cold sore patches
Limited evidence
A thin gel patch worn over the sore. It keeps the area moist so the crust splits less, it stops fingers reaching the sore, and it contains the fluid that spreads the virus. It does not shorten the episode itself, and it is easier to use once the blisters have opened than at the tingle stage.
Four ointments on white: CeraVe Healing Ointment, a Vaseline jar, a petroleum jelly tube and Aquaphor16:9 hero for Petrolatum. Never cropped: the tone strip and the corner logo depend on the full frame.
Limited evidence
Plain ointment dabbed over the crust keeps it soft so it does not split each time you talk or eat, which hurts less and leaves less of a mark. Drying the sore out does the opposite of what people expect. Apply it with a clean fingertip or a cotton bud and wash your hands afterwards - it does nothing to the virus itself.
Cold compress and pain relief
Cold compress and pain relief
Limited evidence
Soreness peaks in the first two days, and a cool damp cloth held on for a few minutes plus ordinary acetaminophen or ibuprofen covers most of it. This is comfort only. It does not shorten the episode or change what is happening in the skin.
Lysine supplements
Lysine supplements
Weak evidence
A popular supplement for preventing episodes, but the studies behind it are small, old and inconsistent. It is not dangerous and some people are convinced by it. It is not a substitute for an antiviral, and it is not something to rely on if your episodes are frequent.

Prescriptions

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These need a prescription.

A white cream tube lying on its side on a white background, with a plain white label reading Penciclovir and a blue swoosh beneath it.
Penciclovir cream
Limited evidence
A prescription antiviral cream applied every two hours while awake for four days. It shortens an episode by around half a day to a day, so a little more than the over-the-counter cream and a lot less than tablets. It is a reasonable option for someone who cannot take the tablets.
A white cream tube lying on its side on a white background, with a plain white label reading Acyclovir and a blue swoosh beneath it.
Acyclovir cream
Limited evidence
The cream version of the tablet, five times a day for four days. The virus is multiplying deep in the skin cells and traveling in a nerve, so a cream only reaches part of the problem, and the benefit is measured in hours rather than days. If you can take the tablets, take the tablets.
A white cream tube lying on its side on a white background, with a plain white label reading Steroid Cream and a blue swoosh beneath it.
Steroid cream on its own
Weak evidence
A steroid cream calms the redness and swelling, which looks like improvement, while leaving the virus free to spread further. It also changes the appearance enough to make the sore hard to recognize later. There is a combination cream that pairs a steroid with an antiviral, but a steroid alone on a cold sore is a step backwards.
An amber pill bottle labeled Valtrex tipped on its side with white tablets spilling out
Strong evidence
The usual first choice, and for a cold sore it is a single day of treatment - two large doses twelve hours apart, started at the first tingle. Taken then, it shortens the episode and can stop a blister forming at all. Started after the blister is out it does much less, which is the whole argument for keeping a course at home.
An amber prescription bottle lying on its side on a white background with a plain white label reading Antivirals, and six small round white tablets spilled out in front of it.
Daily suppressive treatment
Strong evidence
A low dose of the same antiviral taken every day, rather than only during an episode, for people getting roughly six or more a year. It reduces how often they happen substantially and lowers the amount of virus shed in between. The effect stops when the tablets stop, and doctors usually review it after six to twelve months.
An amber prescription bottle lying on its side on a white background with a plain white label reading Famciclovir, and six small round white tablets spilled out in front of it.
Famciclovir
Strong evidence
An equally effective alternative, taken as a single dose at the first tingle, which suits people who will not manage a second dose later in the day. It is used where valacyclovir does not suit or is not available. It is usually the more expensive of the two.
An amber prescription bottle lying on its side on a white background with a plain white label reading Acyclovir, and six small round white tablets spilled out in front of it.
Acyclovir
Strong evidence
The oldest of the antiviral tablets and the cheapest. It works, but it has to be taken five times a day for five days, which is a lot of doses for something that lasts a week anyway. The dose is lowered if your kidneys are not working well.

Procedures

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These are done in the office, usually over several visits.

No procedures listed yet.

When to See a Dermatologist

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Most cold sores never need a dermatologist; with a prescription at home you can handle almost every episode. Get same-day care from urgent care or an eye doctor if a sore appears on or near the eye, or an eye becomes painful, red or light-sensitive during an episode. Get seen urgently if you have eczema and painful blisters or punched-out sores spread beyond the usual spot. Book a dermatology appointment if you get episodes six or more times a year, if a sore has not healed after two weeks, if the area becomes hot, swollen and full of pus with a fever, if you are immune-suppressed or pregnant, or if there is a newborn in the house and you have an active sore. A typical episode needs no test - we diagnose it by looking - and when it looks atypical the base of a freshly opened blister is swabbed for PCR, which is unreliable once a crust has formed.

— Dr. Schwarz, Board Certified Dermatologist

Complications

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Lookalikes

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Impetigo

The one most often confused with a cold sore, because both end up as a golden crust around the mouth. Impetigo is bacterial, so it spreads outward across the skin in patches rather than staying in one small cluster, the crust is thicker and more honey-colored, and there is no tingle a day beforehand. It is also far more common in children, and it is treated with antibiotics rather than antivirals.

Angular cheilitis

Sore, cracked skin at one or both corners of the mouth, often from saliva sitting in the fold, with yeast or bacteria growing in it. It gets mistaken for a cold sore because it is sore, crusted and near the lip. The differences are that it sits only in the corner, it is a split rather than a cluster of blisters, it can be on both sides at once, and it grumbles on for weeks instead of running a ten-day course.

Canker sores

Many people call these cold sores, which is where most of the confusion comes from. Canker sores are shallow round ulcers with a white or yellow floor and a red rim, and they sit inside the mouth on the soft lining, the tongue or the inner cheek. Cold sores sit on the lip border or the skin just outside it. Canker sores are not caused by a virus, they are not contagious, and antivirals do nothing for them.

Myths

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  • "Having cold sores means you have a sexually transmitted infection." Most cold sores are HSV-1, caught in childhood through everyday family contact. HSV-1 can be passed to the genitals through oral sex, and HSV-2 can cause sores on the mouth, so the two are not divided strictly by location. A cold sore on the lip says nothing about how you caught it.
  • "You can only pass it on when there is a blister." An open sore is by far the most contagious moment, but the virus can be shed when nothing is visible. That is part of why it spreads unnoticed.
  • "Cold sores and canker sores are the same thing." They are unrelated. Canker sores are shallow ulcers on the soft lining inside the mouth, not viral and not contagious. Cold sores sit on the lip border.
  • "Once the blister has appeared, treatment is pointless." Antiviral tablets are much less effective once blisters are out, which is why the tingle matters. For a large or painful episode they are still worth taking, and keeping the area moist shortens healing.
  • "Lysine supplements will stop them." The studies are small, inconsistent and mostly old. Lysine is not dangerous, but it is no substitute for an antiviral.
  • "Drying it out makes it heal faster." The opposite. A crust kept soft with plain ointment splits less, hurts less and marks less than one that dries hard and cracks when you talk.
  • "You can catch it from a toilet seat or a swimming pool." The virus does not survive well on surfaces. It passes by direct contact with a sore or infected saliva - kissing, sharing a drink, sharing lip balm.

Questions Patients Ask

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How did I get this?

Almost certainly in childhood, from ordinary contact with someone who carried the virus - a kiss, a shared cup or spoon. Most people have no memory of it, because the first infection often causes nothing. It is not about hygiene or anything you did.

How long am I contagious?

Most easily passed on from when blisters appear until the sore has fully crusted - roughly the first four to five days. Small amounts are shed when nothing is visible. Precautions matter most around newborns, eczema and anyone immune-suppressed.

Why do I always get it in exactly the same place?

Because the virus lives in one nerve, which supplies one small patch of skin. When it reactivates it travels down to that patch. Some people have two or three usual spots.

Will it ever go away for good?

The virus stays in the body permanently, so there is no cure. But episodes usually become less frequent over the years, and daily suppressive treatment can reduce them a great deal. Plenty of people effectively stop having them.

Is it safe to kiss my baby?

Not while you have an active sore. Herpes simplex is dangerous in newborns in a way it is not in older children or adults. Do not kiss the baby, wash your hands before handling them, and cover the sore. If a newborn develops blisters or a fever, or becomes unusually sleepy or floppy, that is an emergency.

Does the treatment work if I start it late?

Less well. Antiviral tablets stop the virus multiplying, and by the time blisters are out most of that has happened. Still worth taking for a severe episode, but the benefit is in the first 24 hours.

References

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