What Causes Herpes? A Dermatologist Explains the Real Causes, How to Tell It Apart from Canker Sores and Shingles, and Effective Treatment
Herpes (herpes simplex) is an infection with the herpes simplex virus (HSV) that causes clusters of clear blisters on a red base, which break into shallow sores within 1–2 days. After the first infection, the virus hides permanently in sensory nerve ganglia and comes back to the same area of skin from time to time for life. It is a condition that can be “controlled”, but there is still no way to remove the virus from the body.
This article is the main guide to everything about herpes. It covers causes, how it spreads, symptoms at each body site, how long it takes to heal, the medicines actually used with their doses and duration, and how to tell it apart from look-alike conditions.
What causes herpes?
Herpes is caused by the herpes simplex virus, which belongs to the Herpesviridae family, the same family as the chickenpox-shingles virus but a different virus. The virus enters the body through tiny breaks in the skin or through moist mucous membranes such as the lips, mouth, conjunctiva, genitals and anus, then multiplies in the upper skin cells until blisters form.
First infection can happen as early as childhood, from being kissed on the cheek, sharing food, or using the same glass or straw. Many people are infected in childhood and never have any symptoms.
Hiding in the nerve ganglia After that, the virus travels along the nerves to settle in a ganglion, such as the trigeminal ganglion for the face and the sacral ganglia for the genitals and buttocks.
Recurrence When local immunity drops temporarily, the virus travels back down the same nerve, so blisters reappear at or near the same spot every time. This is the best feature for telling herpes apart from other rashes.
The World Health Organization estimates that about 2 in 3 people worldwide aged 0–49 carry HSV-1, and about 1 in 8 adults aged 15–49 carry HSV-2. Having herpes is therefore not unusual and has nothing to do with cleanliness.
How do HSV-1 and HSV-2 differ?
HSV-1 was traditionally the virus of the face and lips, but it is now an increasingly common cause of first genital herpes in teenagers and young adults, through oral sex.
HSV-2 is found mostly on the genitals, buttocks and thighs, spreads mainly through sexual contact, and clearly recurs more often than HSV-1 in the same location.
What matters in practice is not “which one is worse” but how often it recurs. Genital herpes from HSV-2 recurs on average 4–5 times in the first year, while from HSV-1 it usually recurs about once a year and becomes less frequent over time. This information is used to decide whether long-term suppressive medication is worthwhile.
Typing the virus can be done with a blood test for type-specific antibodies (type-specific IgG) or by testing the lesion directly for the virus’s genetic material.
How does herpes spread, and when is it contagious?
Herpes spreads through direct contact with skin or mucous membranes carrying the virus. It does not spread through the air, and it is not caught from toilet seats or swimming pools.
The most common routes are kissing, cheek kisses, and oral, vaginal and anal sex.
Sharing items that touch saliva or sores directly, such as glasses, straws, spoons, lip balm and towels, while there is an open sore.
Spreading it with your own hands (autoinoculation) means touching a sore and then rubbing your eyes, picking your nose or touching another area, which is how herpes ends up on a finger or in the eye.
The most contagious period runs from the first burning or itching sensation, before blisters appear, until the sore has completely dried and crusted over.
Asymptomatic shedding is the most important point and most people do not know about it. People with HSV-2 shed virus on the skin without any visible sore on roughly 10–20% of all days. No sore does not mean not contagious, and this is why partners of patients can be infected even though they have “never seen a sore”.
First-time herpes symptoms versus recurrences
Appearance A first infection (primary herpes) is usually much more severe, with several groups of blisters, wide and very painful sores, along with fever, body aches and swollen nearby lymph nodes. In young children it can fill the mouth and gums so they cannot eat (herpetic gingivostomatitis). A recurrence has a single small cluster in the same place, no fever, and heals much faster.
Cause With a first infection the body has no immunity to the virus yet. A recurrence is the same virus in the ganglion being reactivated while the immune system is already keeping it in check.
Severity and urgency Adults with a first episode should always receive an oral antiviral, because it clearly reduces pain and duration. An ordinary recurrence may heal on its own.
When to see a doctor A first episode on the genitals, a first episode in a child who cannot eat or is passing less urine, and any case with high fever or severe headache.
Warning symptoms before blisters (prodrome) are burning, itching, numbness or a stabbing, needle-like pain at the usual spot, appearing about 6–24 hours ahead. This is the golden window to start medicine.
How many days does herpes take to heal, and counted from when?
Count from the day the first blisters appear, not from the day you were exposed.
Incubation period after a first exposure is 2–12 days, about 4 days on average.
A typical recurrence has clear blisters for 1–2 days, shallow sores for 2–3 days, then crusting and complete healing, 5–10 days in total, without scarring if you do not pick at it.
A first infection takes much longer, 2–4 weeks for the sores to heal completely.
Effect of starting medicine early Starting an oral antiviral within the first 48–72 hours, or best of all during the burning or itching stage before blisters appear, shortens the course by about 1–2 days and reduces the number of blisters. If started after the blisters have already broken into sores, the benefit drops a lot.
Signs it is healing are no new blisters appearing 48 hours after starting medicine, and sores that begin to dry with smoother edges. If new blisters keep appearing for more than 5 days, or the sore keeps getting wider, go back to the doctor to review the diagnosis.
Herpes on the mouth and lips
Appearance Small clear blisters in a cluster on the edge of the lip or where the lip meets the skin, breaking into shallow sores and then forming brown crusts, returning at the same corner every time.
Cause Mostly HSV-1 hiding in the facial ganglion, triggered by strong sun, fever, lack of sleep and stress.
Severity and urgency Not dangerous, but highly contagious while the sore is open. Avoid kissing and sharing glasses or straws until the sore has dried.
When to see a doctor When it recurs more than 6 times a year, the sore spreads into the mouth so that you cannot eat, or you are unsure whether it is herpes or a canker sore.
Full details for this location, including a comparison table with canker sores and angular cheilitis, are in the article Cold sores: causes, how long they last, and which medicine really works
1-minute summary clip by Dr. Patara Voravutinon, Dermatologist: Why does a cold sore appear as a clear, burning, itchy blister and come back to the same spot every time? The answer is that the herpes virus (HSV-1) never leaves the body. It hides in the ganglion that supplies the skin in that area. When you are short of sleep, stressed, ill or in strong sun, the virus travels back out along the same nerve, so it appears in the same place, and burning or itching usually comes 6–48 hours before the blister is visible.
Herpes on the nose and around the nostrils
Appearance Blisters or shallow sores on the side of the nose, under the nostril or inside it. It is often more painful than on the lip because the skin here is thin, and it is often mistaken for an inflamed pimple or a sore from nose picking.
Cause HSV-1 in the facial ganglion, as with the mouth. It often follows a cold or frequent nose wiping that breaks the skin.
Severity and urgency Not severe in itself, but this site is close to the eye, so take particular care not to touch it and then rub your eyes.
When to see a doctor When the sore spreads up toward the bridge of the nose or the inner corner of the eye, or there is eye irritation.
Herpes on the fingers and arms (herpetic whitlow)
This answers a question many people search for: “what causes herpes on the arm”.
Appearance Clear or cloudy blisters in a cluster on the fingertip, beside the nail or on the back of the hand, swollen, red and with a deep throbbing pain out of proportion to what you can see. Sometimes it appears as a band along the nerve in the arm.
Cause The virus enters through a break in the skin of the finger, from touching your own herpes sore, biting nails or picking the skin around the nails. In young children it often comes from sucking a finger while they have herpes in the mouth, and it is seen in people whose work involves contact with other people’s saliva or secretions.
Severity and urgency It heals on its own in 2–3 weeks, but it is very painful and is often misdiagnosed as an abscess or ingrown nail and then lanced to drain pus, which does not help and spreads the virus. This is the most important point in this section.
When to see a doctor Every time there is a cluster of blisters on a finger, have a doctor confirm it before letting anyone lance it.
Herpes on the legs, buttocks, thighs and hips
And this answers “what causes herpes on the leg”.
Appearance Clusters of blisters on a red base on the buttocks, the cleft between them, the inner thigh or the back of the thigh, usually on one side and in the same place every time. A dull ache in the buttock or back may come first.
Cause Mostly HSV-2 hiding in the sacral ganglia, which supply the whole band of skin covering the genitals, buttocks and thighs, so a flare can appear outside the genital area.
Severity and urgency Not dangerous, but often mistaken for a pimple on the buttock, an abscess or a friction rash, so people repeatedly get the wrong medicine.
When to see a doctor When blisters return to the same spot more than 2–3 times, because the pattern of “same place, one side, in a cluster” is a key clue to herpes.
Genital herpes
Appearance Several blisters that break into shallow sores with smooth edges, with a sharp burning pain when urine touches them. Women may have more vaginal discharge, and in men it is usually on the shaft of the penis or the foreskin.
Cause Mainly HSV-2, but HSV-1 from oral sex is now an increasingly common cause of first infections in young people.
Severity and urgency The first episode is often severe and the pain may make it impossible to pass urine. Everyone needs an oral antiviral, and screening for other sexually transmitted infections should be done at the same time.
When to see a doctor Everyone with a first episode, everyone who cannot pass urine, and everyone who is pregnant.
Herpes of the eye: a condition that needs a doctor the same day
Appearance Redness in one eye, irritation, watering, sensitivity to light and blurred vision, and there may be blisters on the eyelid or the inner corner of the eye.
Cause HSV-1 spreading to the cornea or conjunctiva, often from rubbing the eye with a finger that touched a sore.
Severity and urgency This is the most urgent condition of the disease. Repeated inflammation of the cornea causes scarring and is a major cause of vision loss from corneal clouding. See an eye doctor the same day.
When to see a doctor As soon as there are eye symptoms together with herpes, and never put steroid eye drops in on your own, because they make a corneal sore spread faster.
Herpes on the trunk and face from contact sports
Appearance Clusters of blisters scattered over the face, neck, shoulders or trunk. In athletes with skin-to-skin contact such as wrestlers and judo players, it is called herpes gladiatorum.
Cause HSV-1 passed on through broken skin during training.
Severity and urgency The first infection often comes with fever and swollen lymph nodes. Stop training until the sores have fully crusted over, to avoid an outbreak in the team.
When to see a doctor When there are blisters in several places with fever, because it must be told apart from chickenpox and a drug rash.
What triggers herpes to flare up?
Triggers differ from person to person. Keeping a note of what came before each flare is more useful than avoiding everything.
Sunlight and UV radiation are the clearest trigger for herpes on the lips. Using a lip balm with SPF 30 or higher before going out in the sun helps reduce flares in this group.
Fever and illness, which is why the English name is “fever blister”.
Lack of sleep and ongoing stress.
Menstruation and hormonal changes.
Injury or procedures in that area such as dental work, tattoos, exfoliation and facial procedures.
Immunosuppressants and steroids, both oral and strong topical ones applied where you have had herpes.
Herpes medicines: creams, tablets and long-term suppression
All herpes medicines are antivirals of the same group. They work by stopping the virus from multiplying in infected cells, so sores heal faster and spread is reduced, but they cannot remove the virus hiding in the ganglion. The drug names below are generic names. Choosing the type, dose and duration is a doctor’s decision based on the site, severity, kidney function and underlying conditions of each person.
Topical creams: limited benefit
Acyclovir 5% cream (topical acyclovir 5% cream) is applied thinly on the blisters 5 times a day for 4 days and shortens the sore by only about half a day to one day.
Penciclovir 1% cream (penciclovir 1% cream) is applied every 2 hours while awake for 4 days.
What to understand Creams suit only infrequent, mild herpes on the lips. They are not a substitute for tablets in a first infection, on the genitals, or in people with weak immunity, and never use a steroid-only cream on a herpes sore because it makes the sore spread wider.
Oral medicine taken per episode (episodic therapy)
Taken only during a flare, started as early as possible, from the burning or itching stage before blisters appear.
Acyclovir For herpes on the mouth, 400 mg 3 times a day for 5 days · first genital herpes, 400 mg 3 times a day for 7–10 days · genital recurrence, 800 mg twice a day for 5 days. The downside is that it must be taken often and the doses spaced on time.
Valacyclovir is absorbed better so it is taken less often. For herpes on the mouth, 2 g twice a day for just 1 day · first genital episode, 1 g twice a day for 7–10 days · recurrence, 500 mg twice a day for 3 days.
Famciclovir For herpes on the mouth, 1,500 mg as a single dose · first genital episode, 250 mg 3 times a day for 7–10 days · recurrence, 1 g twice a day for 1 day.
Signs it is working No new blisters within 48 hours of starting medicine, and the sore dries faster than in earlier flares when you took no medicine · Signs it is not working Blisters still appearing after the full 5 days, a widening sore, or pus and thick yellow edges, which point to a secondary bacterial infection that needs a different medicine.
Oral medicine for long-term suppression (suppressive therapy)
This means taking a low dose every day continuously. It suits people who have about 6 or more recurrences a year, people whose recurrences badly affect work or relationships, and couples in which one partner does not carry the virus.
Acyclovir 400 mg twice a day, every day
Valacyclovir 500 mg once a day, or 1 g once a day when there are more than 10 recurrences a year
Famciclovir 250 mg twice a day
Expected results Recurrences can be reduced by about 70–80%, and studies in couples where one partner has HSV-2 found that taking valacyclovir once a day cut transmission to the partner by about half, but not to zero, so condoms are still needed. Results vary from person to person.
Follow-up Review the need with your doctor every 12 months, because recurrences often become less frequent over time on their own, and check kidney function in people with kidney disease and in older adults.
Herpes in pregnant women and newborns
Appearance Symptoms in the mother are no different from anyone else, but the risk lies in passing the virus to the baby during delivery through a birth canal with sores.
Cause of the highest risk is a first infection in the third trimester, because the mother has no antibodies yet to pass to the baby. The risk is very different from a recurrence of an existing infection.
Approach used in practice Doctors usually give oral acyclovir as suppression from about 36 weeks of pregnancy until delivery, to reduce the chance of sores on the day of delivery, and consider a caesarean section when there are sores or warning symptoms during labour.
When to see a doctor Every pregnant woman who suspects a first episode of herpes must tell her obstetrician immediately, not wait for the next antenatal visit.
In newborns herpes is a severe condition that can spread into the bloodstream and nervous system and must be treated in hospital with intravenous antiviral medicine. Rush the baby in if the baby becomes drowsy, will not feed, has a fever, or has blisters, even just a few.
Herpes in people with weak immunity
Appearance Sores wider than usual, with deep edges, healing slowly beyond 2 weeks, and sometimes turning into chronic sores that do not look like ordinary herpes and are hard to diagnose.
Who is in this group People with HIV and low immunity, cancer patients on chemotherapy, organ transplant recipients, and people on continuous immunosuppressants.
Severity and urgency Higher and longer doses are needed, some people need intravenous treatment, and acyclovir-resistant virus may occur, which requires switching to another group of medicines.
When to see a doctor Whenever sores do not improve at all after finishing the course, or get larger while on treatment.
Special precaution People with severe atopic dermatitis can develop a condition in which the herpes virus spreads over the whole rash area (eczema herpeticum), with blisters and small punched-out dents scattered over a wide area along with fever. This condition needs treatment quickly.
How to tell herpes apart from look-alike conditions
The most helpful shared feature is clustered blisters on a red base, in the same place, on one side, with burning before they appear
Canker sore (aphthous ulcer) is inside the mouth, on the inner cheek and tongue, does not start as a blister and is not contagious. Herpes starts on the outer edge of the lip, or on the gums and hard palate.
Shingles is caused by a different virus. The blisters line up in a long band along a nerve and stop at the midline of the body, it hurts more, and it usually happens only once in a lifetime, whereas herpes appears in small clusters and comes back.
Angular cheilitis is at the corners of both sides of the mouth, as red, peeling cracks rather than blisters, and is often linked to yeast or pooled saliva.
Hand, foot and mouth disease has blisters appearing together on the palms, soles and inside the mouth, is seen in children and spreads in groups.
Chickenpox has blisters scattered over the whole body including the scalp, in several stages at once, not clustered in one spot.
Bacterial impetigo has honey-yellow crusts around the mouth and nose, spreads quickly and does not return in the same place.
Primary syphilis sore is a single sore with a firm edge that is painless, unlike herpes, which is clearly painful. This matters because both can be in the same location.
Diagnosing herpes
Most of the time a dermatologist can diagnose it from the look of the sore and the history of recurrence in the same place. Extra tests are used when the picture is unclear or confirmation is wanted.
Testing the sore for the virus’s genetic material (PCR) is the most accurate and tells whether it is HSV-1 or HSV-2. The swab should be taken from a freshly broken blister, because a crusted sore may give a negative result even when it is herpes.
Viral culture can be used but is more sensitive to the timing of collection.
Blood test for type-specific antibodies (type-specific IgG) shows which type you have had in the past. It does not show whether the sore you have now is herpes, and the result takes 2–12 weeks after infection to appear, so it is more useful for counselling couples than for diagnosing an acute sore.
A test that should no longer be relied on is the Tzanck smear alone, because it cannot tell HSV from the chickenpox-shingles virus.
Complications of herpes to watch for
Secondary bacterial infection of the sore from picking and scratching. Look for pus, thick yellow crusts, and swollen red skin spreading around the sore.
Inflammation of the cornea, a major cause of vision loss from corneal clouding.
Inflammation of the brain and its coverings is uncommon but serious. Signs are high fever, severe headache, confusion or seizures, and you must go to hospital immediately.
Erythema multiforme rash is a target-like ring rash that follows herpes by about 1–2 weeks. In people who have frequent recurrences, long-term suppressive medicine may be needed to break this cycle.
Spread of the virus over atopic dermatitis as described above.
Psychological impact, especially with genital herpes, which often affects people more than the disease itself. Correct information on how common it is and how it can be controlled helps more than you might expect.
Preventing spread and preventing recurrences
While you have a sore avoid kissing, avoid sexual contact of every kind including oral sex, and do not share glasses, straws, spoons, lip balm, towels or razors until the sore has crusted over and dried completely.
Wash your hands every time you touch a sore and never rub your eyes. This is the most effective way to prevent herpes of the fingers and the eye.
Use a condom every time It reduces the risk a great deal but not completely, because it does not cover all the skin that can shed virus.
Talk with your partner first It is difficult but is the most effective real step to reduce transmission, together with considering long-term suppressive medicine in couples where one partner does not yet carry the virus.
Do not go near a newborn while you have a sore on your mouth and do not kiss the baby. This is the point people neglect most and it has the most serious consequences.
Reduce recurrences by applying sunscreen lip balm before going out in the sun, sleeping enough, managing stress, and telling your dermatologist or dentist that you have had herpes before any procedure on the face or mouth, so that preventive medicine can be considered.
Common myths about herpes
“Having herpes means being unfaithful” Not true. Most HSV-1 is caught in childhood, and a first infection may cause no symptoms at all for many years before the first outbreak. A first sore today therefore does not mean the virus was caught today.
“No sore means not contagious” Not true, as explained in the section on asymptomatic shedding.
“Herpes is the same as molluscum or a pimple” No. Herpes always has clear blisters and burning that comes first.
“Putting toothpaste or salt on it dries it faster” It does not help, and it irritates the skin around the sore so that the sore gets wider.
“Popping the blister to let the fluid out makes it heal faster” The opposite. The fluid in the blister is full of virus, and popping it spreads the virus and risks a secondary bacterial infection.
“One dose of medicine cures it completely” No medicine today removes the virus from the ganglion. The aim of treatment is for sores to heal faster, recur less often and spread less.
When to see a doctor
Eye symptoms of any kind, whether redness, irritation, sensitivity to light or blurred vision — see a doctor the same day.
A first episode, especially on the genitals, or with fever and swollen lymph nodes.
The sore has not improved at all within 10 days, or new blisters keep appearing after finishing the medicine.
Pus, thick yellow crusts, or swollen red skin spreading around the sore.
Recurring more than 6 times a year, or clearly affecting daily life.
Pregnant, weak immunity, or already having severe atopic dermatitis.
A newborn with blisters, drowsiness or not feeding — this is an emergency.
Key points
Herpes is caused by the herpes simplex virus, which hides permanently in the nerve ganglia, so it can recur in the same place for life, and there is still no medicine that removes the virus.
The best clue for telling herpes apart from other conditions is clustered blisters on a red base, in the same place, on one side, with burning or itching 6–24 hours beforehand.
A typical recurrence heals in 5–10 days, while a first infection takes 2–4 weeks.
Oral antivirals work best when started within the first 48–72 hours, and people who have about 6 or more recurrences a year should discuss long-term suppressive medicine with a doctor.
No sore does not mean not contagious, because the virus can shed on the skin without symptoms on roughly 10–20% of days.
The only things that need to be rushed are eye symptoms and blisters in a newborn. For both, see a doctor immediately and do not wait and watch.
Frequently asked questions
How many days does herpes take to heal?
For an ordinary recurrence, counting from the day the first blisters appear, clear blisters last 1–2 days, shallow sores another 2–3 days, then crusting and complete healing take about 5–10 days in total. A first infection takes much longer, 2–4 weeks, because the body has no immunity to the virus yet. Taking an antiviral from the stage when you first feel burning or itching, before blisters appear, shortens the course by about 1–2 days and gives fewer blisters, but if started after the blisters have broken into sores the benefit drops a lot. The sign that it is healing is no new blisters appearing 48 hours after starting medicine.
Is herpes dangerous?
In generally healthy people, herpes on the mouth and genitals is not life-threatening. It is mostly a matter of pain, annoyance and spread, but there are three situations that are truly dangerous and urgent. The first is herpes of the eye, because repeated inflammation of the cornea can cause scarring and loss of vision. The second is herpes in a newborn, which can spread into the bloodstream and nervous system and must be treated in hospital. The third is herpes in people with weak immunity or severe atopic dermatitis, where the sores spread wide and heal much more slowly than usual.
What causes herpes on the arm?
Herpes on the arm, fingers or back of the hand is caused by the same virus, entering through a tiny break in the skin there. The most common route is touching your own herpes sore and then picking the skin around the nails or biting the nails. In young children it often comes from sucking a finger while they have herpes in the mouth. When it appears on a finger it is called herpetic whitlow, with a small cluster of blisters that is swollen and has a throbbing pain deeper than what you can see. The key point is that it is often misdiagnosed as an abscess or ingrown nail and then lanced to drain pus, which does not help and spreads the virus, so always have a doctor confirm it first.
What causes herpes on the leg?
Herpes on the leg, thigh, buttock or hip is mostly caused by HSV-2 hiding in the sacral ganglia, which supply the whole band of skin from the genitals to the buttocks and thighs, so a flare can appear outside the genital area. It shows as clustered blisters on a red base, on one side and in the same spot every time. Some people have a dull ache in the buttock or back 1 day beforehand. This location is often mistaken for a pimple on the buttock, an abscess or a friction rash, so people get the wrong medicine repeatedly. If blisters return to the same spot more than 2–3 times, have a doctor examine and confirm it.
Herpes treatment: what to do to heal fastest?
Only a few things really help. The first and most important is to start an oral antiviral as early as possible, from the burning or itching stage before blisters appear. The medicines used are acyclovir, valacyclovir or famciclovir, with doses and number of days that differ by location and whether it is a first episode or a recurrence, and the doctor chooses them. The second is to keep the sore clean, not pick it, not pop the blisters, and use a brief cold compress to ease pain. The third is to get enough rest and avoid strong sun on the affected area. Topical creams help only a little and suit only mild herpes on the lips. Toothpaste, salt and popping the blisters do not help and make the sore worse.
Can herpes be cured completely, and why does it come back?
At present no medicine can remove the herpes virus from the body, because after the first infection the virus settles in sensory nerve ganglia, which medicines cannot reach and the immune system cannot clear. When local immunity drops temporarily, for example with strong sun, fever, little sleep, stress or menstruation, the virus travels back along the same nerve, so it always appears in the same spot. What can be done is to control the disease well, meaning fewer recurrences, faster healing and less spread. The good news is that in most people the frequency of recurrences often falls on its own over time, and people who recur often can use long-term suppressive medicine, which reduces the number of episodes by about 70–80%.
Read more about other skin conditions in Skin disease articles by specialist doctors
The information in this article is for education and is not a diagnosis or a treatment order for any individual. The drug names mentioned are generic names for understanding. The choice of drug type and dose must be assessed and prescribed by a doctor only. Treatment results vary from person to person.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed September 22, 2026
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