Chickenpox (Varicella): Causes, Symptoms, Treatment and Prevention
Updated: 3 days ago
Cover image: F malan · CC BY-SA 3.0 · cropped
Chickenpox, medically known as varicella, is a viral infection caused by the Varicella-Zoster Virus (VZV). It causes a fever together with a clear, fluid-filled blistering rash that appears over the body in waves. The spots are at different stages at the same time: some are blisters, some are pustules, and some have already crusted over. This is the feature that sets chickenpox apart from other blistering rashes.
The short answer to the question people search for most: counting from the first day of the rash, new spots keep appearing for another 3-5 days, and every spot has crusted over within 7-10 days. You are contagious from 1-2 days before the rash appears until the last spot has dried and crusted, and antiviral medicine works best when it is started within the first 24 hours after the rash appears, not after that.
This article is written by a dermatologist. It explains the timeline of the illness stage by stage, how to tell chickenpox spots apart from hand, foot and mouth disease, cold sores, shingles and insect bites, the medicines actually used with their doses and duration, the medicines that must never be used, and the questions people ask after recovery: pitted scars and immunity testing.
What is chickenpox and what causes it?
Chickenpox is caused by the Varicella-Zoster Virus, a member of the herpes virus family (Human herpesvirus 3). This virus has two special properties worth knowing from the start.
It spreads very easily. Among people without immunity who live in the same household as a patient, the infection rate is as high as about 85-90%. In other words, if one person in the home has it, someone who has never had chickenpox and has never been vaccinated is almost certain to catch it.
It does not leave the body. After recovery, the virus stays quietly in the sensory nerve ganglia beside the spinal cord for life, and it can return as shingles (Herpes zoster) when immunity declines.
In Thailand, cases occur all year round, but outbreaks tend to increase from January to March, when the weather is cool and schools reopen, so children spend time together in enclosed classrooms.
How does chickenpox spread, and when is it contagious?
Chickenpox spreads in 3 ways.
Droplets from coughing, sneezing or talking. This is the main route. The virus can stay in the air of a closed room for a while, so you can catch it without touching the patient directly.
Direct contact with the fluid in the blisters. The clear fluid contains a large amount of virus. Scratching the blisters and then touching objects spreads it.
Contact with items soiled by fluid from the blisters, such as towels, pillowcases and clothing.
The contagious period is the point people misunderstand most. A patient can spread the virus from 1-2 days before the rash appears, when nobody yet knows they are ill, and continues to spread it until every blister has dried and crusted over, which usually takes about 5-7 days after the rash appears. Isolation should therefore be counted from how the spots look, not from the day the fever goes down.
A person with shingles can also spread VZV, but mainly through direct contact with the blisters, and a person who catches the virus from someone with shingles will develop chickenpox, not shingles.
Incubation period of 10-21 days: what to watch for after exposure
After infection, the virus takes 10-21 days (on average 14-16 days) before symptoms begin. During this time there are no symptoms and no test can detect anything yet.
What to do during this period if you know you were exposed
Note the day of exposure clearly and keep watching until day 21.
If you have never had chickenpox and have never been vaccinated, getting the vaccine within 3-5 days after exposure can still prevent the illness or reduce its severity.
High-risk groups, namely pregnant women without immunity, newborns and people with weakened immunity, should see a doctor immediately after exposure, because they may need varicella-zoster immune globulin (VZIG), which works best when given within 96 hours.
The 4 stages of the chickenpox rash and the timeline: how many days until it clears
The chickenpox rash follows a predictable order. Each spot takes about 24-48 hours to go through all 4 stages.
Flat red spot stage (macule): It starts as a small red spot 2-4 millimetres across that is not yet raised.
Raised bump stage (papule): Within a few hours the red spot rises into a bump.
Clear blister stage (vesicle): It becomes a thin-walled, clear blister on a red base, which textbooks describe as a 'dewdrop on a rose petal'. This is the itchiest stage.
Cloudy blister and crusting stage (pustule/crust): The fluid in the blister turns cloudy, the centre sinks in to form a dimple, and then it dries into a crust. The crust falls off by itself within 1-3 weeks.
The overall timeline that answers 'how many days until it clears'
Day -2 to 0: Low-grade fever, headache, tiredness and loss of appetite (young children may skip this stage entirely, with the rash as the first sign).
Day 1-5: The rash appears in waves, one crop a day, usually starting on the scalp, face and trunk and then spreading to the arms and legs.
Day 5-7: Most spots crust over and the fever goes down. You stop being contagious once every spot has crusted over.
Day 7-10: The crusts are completely dry. You can return to school or work.
Week 2-3: The crusts fall off, leaving red or dark marks that fade over another 2-6 months.
The total number of spots in an unvaccinated child is about 200-500. People who were vaccinated but still catch it (breakthrough varicella) usually have fewer than 50 spots, a lower fever and a quicker recovery.
What do chickenpox spots look like, and how can you tell it is chickenpox?
Image: Ronny Ager-Wick · CC BY-SA 3.0
Three signs let you confirm it with reasonable confidence.
Spots at several stages at the same time in the same area. This is the most reliable sign. If you look at the back or chest and see flat red spots, clear blisters and crusts mixed together within the area of one palm, it is almost always chickenpox. Other diseases usually come out together as a single batch.
Spots on the scalp. If you run your hand through the hair and feel bumps or crusts on the scalp, that is an important clue, because allergic rashes, insect bites and hand, foot and mouth disease usually do not appear on the scalp.
Sores in the mouth, on the palate or on the tongue together with a rash all over the body. The spots on the lining of the mouth break quickly into shallow sores, which makes swallowing painful.
The distribution also helps. Chickenpox is centripetal, meaning the spots are densest on the trunk, face and scalp and thinner toward the forearms and lower legs, the opposite of hand, foot and mouth disease, which is densest on the hands and feet.
Telling chickenpox apart from hand, foot and mouth disease
These two diseases are confused most often in children because both have blisters and mouth sores.
Appearance: In hand, foot and mouth disease the blisters are oval, somewhat like grains of rice, with thicker walls that break less easily. In chickenpox the blisters are round with thin, clear walls that break easily.
Location: Hand, foot and mouth disease mainly appears on the palms, soles, around the mouth and on the buttocks, and does not appear on the scalp. Chickenpox appears all over the body, including the scalp.
Severity and urgency: Hand, foot and mouth disease usually clears by itself within 7-10 days, and the main problem is that children refuse to drink and become dehydrated. Chickenpox in adults and in people with weak immunity carries a higher risk of complications.
When to see a doctor: For both diseases, see a doctor if the child is drowsy, refuses to drink, passes less urine, or has a high fever for more than 3 days.
For more detail on how to tell them apart, read Hand, foot and mouth disease (HFMD) and how to tell its blisters from cold sores and chickenpox
Telling chickenpox apart from cold sores and shingles
All three are caused by viruses from the same family and all cause clear blisters, but the patterns of distribution are clearly different.
Appearance: Cold sores are a single cluster of small blisters grouped together, about the size of a one-baht coin, in the same place again and again, such as the lips or the genitals. Shingles is a group of blisters in a long band along a nerve, on one side only and stopping at the midline, while chickenpox spreads over the whole body on both sides.
Cause: Cold sores are caused by the HSV virus. Shingles is the same VZV that once caused chickenpox, returning again.
Severity and urgency: Shingles has a 72-hour rule: antiviral medicine should be started within the first 3 days to reduce the chance of long-lasting nerve pain. Chickenpox has an even narrower window of 24 hours.
When to see a doctor: Shingles on the face, around the eye or on the tip of the nose needs to be seen by a doctor the same day, because of the risk to vision.
Read more at Cold sores: what causes them and how to tell them from mouth ulcers and shingles and Shingles: what causes it and the 72-hour rule for urgent treatment
Telling chickenpox apart from insect bites, allergic rashes and impetigo
Insect bites: The bumps are usually limited to skin that is exposed outside clothing, such as the arms, legs and ankles, scattered in patches or in a line, with no fever beforehand, and they do not appear in the mouth or on the scalp.
Drug rashes and hives: These are red raised patches with unclear edges that can move within a few hours and itch intensely. They are not clear blisters that form crusts.
Impetigo: These are blisters or pustules that break and leave a honey-yellow golden crust, usually around the mouth and nostrils, with little fever, and they do not appear all over the body at the same time. The important point is that chickenpox that has been scratched until it becomes infected with bacteria can turn into impetigo on top of it, which makes the crusts turn golden yellow, produces pus and becomes more painful. That is the signal to see a doctor.
Chickenpox in adults: why the symptoms are worse than in children
This is the second most searched question after 'how many days until it clears', and the answer is that it really is worse, and this is not a myth.
Appearance: Adults usually have a higher fever, several days of early symptoms before the rash appears, a lot of body aches, more spots, and spots that are often larger.
Cause: The immune response in adults is stronger, which causes more inflammation. In addition, adults often have underlying conditions or smoke.
Severity and urgency: The complication that clearly differs from children is varicella pneumonia, which occurs in about 1 in 400 adults and is the main reason for hospital admission. The risk factors are smoking and pregnancy. The death rate in adults is many times higher than in school-age children.
When to see a doctor: Every adult with chickenpox should see a doctor from the first day the rash appears, because adults are a group with an indication for antiviral medicine, and if there is cough, shortness of breath or fast breathing around day 3-5 after the rash appears, go to the hospital immediately.
Chickenpox in pregnancy and in newborns
This group is a medical emergency, not something to watch at home.
Pregnancy before 20 weeks: There is a risk of congenital varicella syndrome of about 0.4-2%, which causes skin scarring in the baby, short and deformed limbs, and eye and brain abnormalities.
Pregnancy in the 2nd-3rd trimester: The mother has a higher risk of pneumonia, so there is an indication for antiviral medicine.
Delivery from 5 days before to 2 days after the mother's rash appears: The baby is at risk of severe neonatal varicella, because the baby receives the virus without having received immunity from the mother. The baby needs VZIG and monitoring in hospital.
A pregnant woman without immunity who has been exposed: She must contact a doctor immediately and should not wait for a rash, because VZIG must be given within 96 hours.
The chickenpox vaccine is a live vaccine, so it must not be given during pregnancy, and contraception should continue for another 1 month after the injection. Women planning a pregnancy should have their immunity tested and complete the vaccine before becoming pregnant.
Antiviral medicines: what are they, who should get them, and within how many hours must they be started
The main medicine is acyclovir and medicines in the same group. The key is timing. Medicines in this group work by stopping the virus from multiplying, so they help most while the virus is still dividing, which is the first 24 hours after the rash starts. If started later than that, the benefit becomes smaller and smaller.
Commonly used doses (the doctor adjusts them according to weight, kidney function and severity)
Oral acyclovir in adults and teenagers over 12 years: 800 milligrams 5 times a day for 5-7 days.
Oral acyclovir in children: 20 milligrams per kilogram of body weight per dose, 4 times a day (no more than 800 milligrams per dose) for 5 days.
Valacyclovir in adults: 1,000 milligrams 3 times a day for 5-7 days. The advantage is taking it 3 times a day instead of 5, so it is easier to finish the course.
Famciclovir in adults: 500 milligrams 3 times a day.
Intravenous acyclovir: For people with weakened immunity, pneumonia, encephalitis, or newborns. Treatment must be given in hospital.
Who has an indication for antiviral medicine
Everyone over 12 years old, including teenagers and adults
Pregnant women in the 2nd and 3rd trimesters
People with weakened immunity, and people taking immunosuppressants or steroids
People with chronic skin conditions such as atopic dermatitis, or chronic lung disease
People who regularly take salicylate-type medicines
The second person in a household, who usually receives a larger dose of virus than the first and has more severe symptoms.
Healthy children under 12 years old with mild symptoms generally do not need antiviral medicine, because the illness clears by itself and the benefit is fairly small. The medicine only shortens the fever by about 1 day and reduces the number of spots somewhat.
The sign that it is working is no new spots appearing 48-72 hours after starting the medicine and the fever going down. If after 72 hours new spots are still appearing or the fever rises, go back to the doctor to be assessed for complications or a secondary infection. The choice of medicine, dose and duration is a decision for the doctor who examines the patient. Do not buy antiviral medicine to take yourself or use leftover medicine from someone else.
Reducing fever and itch: medicines you can use and medicines you must never use
Fever medicines you can use
Paracetamol (Paracetamol / Acetaminophen) at 10-15 milligrams per kilogram of body weight per dose in children, or 500 milligrams 1-2 tablets in adults, every 4-6 hours when there is a fever, no more than 4 grams a day.
Medicines to avoid: these two groups matter more than many people think
Never use aspirin and any salicylate-group medicine in children and teenagers. They are linked to Reye's syndrome, which causes sudden liver failure and brain swelling and can be fatal. Take special care with this, because some cold and pain-relief formulas contain salicylates without the name on the box saying so directly.
Avoid non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, because there is evidence linking them to severe, spreading streptococcal bacterial infection in people with chickenpox.
Medicines and ways to reduce itch
Calamine lotion: Apply a thin layer on the spots as often as needed. Do not apply it on spots that have broken into open sores.
Oral antihistamines such as chlorpheniramine or hydroxyzine at 0.5 milligrams per kilogram per dose in children help with sleep on nights when the itch is severe. The main side effect is drowsiness.
A cold compress or a lukewarm, not hot, bath for 10 minutes truly reduces itch and is the safest option.
Cut nails short and put cotton gloves on young children at night. In practice this is the measure that reduces scarring the most.
Strong steroid-containing creams are not recommended on chickenpox spots, because they suppress immunity locally and increase the chance of a secondary bacterial infection.
Can you bathe, what must you not eat, and myths to correct
You can bathe, and you should. The old belief that you must not get wet is wrong. Bathing in lukewarm, not hot, water with a mild fragrance-free soap reduces the bacteria on the skin and lowers the chance of a secondary infection. After bathing, pat gently with a clean cloth and never rub.
There are no foods that must be avoided because of this disease. Eggs, pickled foods and meat do not make the rash flare up or increase scarring. What should be avoided is spicy, sour or hard food in people with mouth sores, because it makes eating too painful.
Do not pick the crusts. This is the restriction that has the most real effect. Picking causes both secondary infection and permanent pitted scars.
Do not apply herbs, leaves or powder on spots that have broken, because this increases the chance of infection and makes the rash harder to assess.
How many days until it clears, how long off school or work, and when can you go back
The criterion is how the spots look, not the number of days. A patient can return to school or work when every spot has crusted over and dried, with not a single clear blister left. In practice this usually matches day 5-7 after the rash appears, and in some cases up to day 10.
People who were vaccinated but still caught it may have only small red bumps without any blisters at all. In this case the criterion is no new lesions appearing for 24 hours.
During isolation, sleep in a separate room, use separate towels and bedding, and avoid being with high-risk people: pregnant women without immunity, babies under 1 year old, and people taking immunosuppressants.
Complications to watch for
Although most cases clear by themselves, these complications do occur.
Secondary bacterial skin infection is the most common in children, usually caused by Staphylococcus aureus or Streptococcus pyogenes. Look for spots that turn to pus, redness and warmth that spreads outward, more pain, or a fever that returns after it had gone down.
Viral pneumonia is more common in adults, pregnant women and smokers. It usually starts on day 3-5 after the rash appears with cough, shortness of breath and fast breathing.
Cerebellar inflammation (cerebellar ataxia) occurs in about 1 in 4,000 children. The signs are an unsteady walk, being unable to keep balance, and slurred speech. It usually occurs in the first week after the rash and clears by itself over several weeks.
Encephalitis is less common but severe. The signs are drowsiness, seizures and confusion.
Dehydration from mouth sores that make swallowing impossible, which is common in young children.
Pitted chickenpox scars: how to prevent and treat them
Most chickenpox scars are not caused by the disease itself but by scratching and secondary bacterial infection, which damage the skin as deep as the dermis. The typical appearance is a round, sharp-edged depression 2-6 millimetres across, usually on the forehead, cheeks and upper trunk.
Prevention while you still have the illness is when you can do the most
Cut nails short, wear cotton gloves at night, and use antihistamines to help sleep on nights when the itch is severe.
Keep the skin clean and bathe every day to lower the chance of secondary infection.
See a doctor immediately when pus begins to appear, because treating a secondary infection early is what truly reduces scarring.
After the crusts have fallen off
The red or dark marks that remain are not scars and will fade by themselves within 2-6 months. What speeds up fading is regular sun protection with sunscreen of SPF 30 or higher, because sunlight makes the pigment darker and keeps it longer.
Pitted scars that have already formed do not go away by themselves and do not respond to ordinary creams. The evidence-based approach is procedures such as releasing the fibrous bands under the depression (subcision), filler injections, and fractional carbon dioxide laser, which need to be done several times and give results that differ from person to person. They should be considered starting at least 3-6 months after the rash has completely cleared.
For the raised scars that are sometimes seen, read the guide to scar creams at Scar creams: which to choose and how long to apply before you see results
Can you get it again, and why does the virus come back as shingles
Chickenpox can recur, but this is very rare. Most people who have had it develop lifelong immunity. People who get it again are usually those who had it for the first time before the age of 1 year, those whose first illness was so mild that immunity did not build up fully, or those with weakened immunity.
What is more common than a recurrence is its return as shingles, because after recovery the virus is not removed from the body but hides in the nerve ganglia. When immunity falls because of older age, stress, illness or immunosuppressant medicine, the virus travels back along the nerve to the skin. About 1 in 3 people who have had chickenpox will have shingles at some point in life, and the risk rises clearly after the age of 50.
Blood test for IgG: how to tell whether you have already had it
Many people cannot remember whether they have had it, especially adults who are planning a pregnancy, working in a hospital, or about to receive immunosuppressant medicine. The method that gives a clear answer is a blood test for VZV IgG antibodies.
A positive VZV IgG means you already have immunity, whether from past infection or from the vaccine, and generally no further vaccine is needed.
A negative VZV IgG means you do not yet have immunity and should have 2 doses of the vaccine, especially if you are a healthcare worker, a teacher, or a woman planning a pregnancy.
VZV IgM is used to look for acute infection, not old immunity, so it is not the test used to answer the question 'have I had it?'
Remembering that you had pitted scars on the face or trunk is fairly good indirect evidence, but it is not as certain as a blood result.
Chickenpox vaccine: who should get it and how many doses
The chickenpox vaccine is a live attenuated vaccine that prevents about 92% of disease of any severity and more than 98% of severe disease when the full 2 doses are given.
Children: The first dose at 12-15 months and the second dose at 4-6 years.
Aged 13 years and over without immunity: 2 doses, 4-8 weeks apart.
Vaccination after exposure to a patient: If given within 3-5 days after exposure, it can still prevent the illness or reduce its severity.
Must not be given to: pregnant women, people with severely weakened immunity, and people allergic to a component of the vaccine.
People who are vaccinated but still catch it have much milder symptoms, with fewer than 50 spots, a low fever and almost no scarring.
When to see a doctor
See a doctor the same day if you have any of the following
Older than 12 years or an adult, so that antiviral medicine can be considered within the 24-hour window
Pregnant, or a baby under 1 year old
Weakened immunity, or regularly taking immunosuppressants or steroids
Cough, shortness of breath, fast breathing or chest pain
Drowsiness, confusion, seizures, stiff neck, an unsteady walk or being unable to keep balance
Spots that turn to pus, skin around the spots that is red and warm and spreading outward, or a fever that returns after it had gone down
Spots or redness and pain in or around the eye
Unable to eat or drink because of mouth sores, or passing less urine
In brief
Chickenpox is caused by the VZV virus, with an incubation period of 10-21 days, a rash that keeps appearing for 3-5 days, and crusting of every spot within 7-10 days.
The distinctive feature used for diagnosis is seeing spots at several stages at the same time, together with spots on the scalp and sores in the mouth.
You are contagious from 1-2 days before the rash appears until every spot has crusted over. Returning to school or work is based on dry crusts, not on the number of days.
Adults really do get more severe illness than children and have an indication for acyclovir, which should be started within the first 24 hours after the rash appears.
Never use aspirin or salicylate-group medicines in children and teenagers, because of the risk of Reye's syndrome, and avoid NSAIDs.
Pitted scars can be prevented while you still have the illness by not scratching and by treating a secondary infection quickly.
What to do if you have it today: If you are over 12 years old, pregnant or have weak immunity, see a doctor on the first day the rash appears. Healthy children should be cared for according to symptoms, with nails cut short and a watch kept for the warning signs above.
Frequently asked questions
How many times can a person get chickenpox?
Generally just once in a lifetime, because after recovery the body builds immunity that lasts a long time. However, recurrence has been reported in a very small proportion of people, usually those who had it for the first time before the age of 1 year, those whose first illness was so mild that immunity did not build up fully, and those with weakened immunity. What is more common than a recurrence is the same virus returning as shingles, which happens in about 1 in 3 people who have had chickenpox and becomes more common after the age of 50.
How do you know it is chickenpox?
The best confirming sign is seeing spots at several stages at the same time in one area, with flat red spots, clear blisters, cloudy blisters and crusts mixed together within an area about the size of one palm. The second sign is to run your hand over the scalp: finding bumps or crusts in the hair helps a lot, because similar diseases such as hand, foot and mouth disease or insect bites usually do not appear there. The third sign is shallow sores in the mouth or on the palate, and there is often a low-grade fever one to two days before the rash. If you are still unsure, see a doctor before buying medicine yourself, because the window of time for antiviral medicine is narrow.
How can you make chickenpox clear up quickly?
Only a few things really help. The first, if you are in a group with an indication (older than 12 years, adults, pregnant women in the second and third trimesters, people with low immunity, or the second person in a household), is starting the antiviral acyclovir within the first 24 hours after the rash appears, which reduces the number of spots and the length of the fever. The second is to get enough rest, drink plenty of fluids, and eat soft food if you have mouth sores. The third is to keep the itch under control with calamine and antihistamines, because not scratching makes it clear faster and avoids scarring. What does not help is avoiding certain foods or applying herbs on the spots.
How many days does chickenpox take to clear?
Counting from the first day of the rash, new spots keep appearing in waves for about another 3-5 days. After that the spots start to crust, and every spot has crusted within 7-10 days. The crusts then fall off by themselves over another 1-3 weeks, and the red or dark marks that remain fade within 2-6 months. In adults it usually takes somewhat longer than in young children and there are more spots. People who were vaccinated but still caught it usually clear faster and have fewer than 50 spots. For returning to school or work, look at whether every spot has crusted and dried, not the number of days.
What must you avoid with chickenpox?
There are three restrictions that truly matter. The first is not to pick the crusts or scratch the spots, because this is the main cause of both secondary bacterial infection and permanent pitted scars. The second is not to take aspirin or medicines containing salicylates in children and teenagers, because of the risk of Reye's syndrome, which causes liver failure and brain swelling, and to avoid ibuprofen as well. The third is not to apply herbs, leaves or powder on spots that have broken. The beliefs that you must not bathe and must not eat eggs are incorrect. Bathing in lukewarm water with mild soap every day helps reduce secondary infection, and food does not make the rash flare up.
How do you tell whether you have already had chickenpox?
The method that gives the clearest answer is a blood test for VZV IgG antibodies. A positive result means you already have immunity, whether from past infection or from the vaccine, and generally no further vaccine is needed. A negative result means you do not yet have immunity and should have two doses of the vaccine. The test is very useful for women planning a pregnancy, healthcare workers, teachers, and people about to receive immunosuppressant medicine. Looking for pitted scars on the face or trunk is reasonably reliable indirect evidence, but it is not as certain as a blood result, and not remembering having had it does not mean you have not had it.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed September 16, 2026
Read other articles on skin conditions at All skin condition articles
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