Fever With Rash: What Causes It? A Dermatologist Tells 10 Diseases Apart in Children and Adults, When the Rash Appears, Whether It Is Contagious, How Long It Lasts, and When to Go to Hospital Fast
Fever with rash (febrile exanthem) is a fever together with a rash on the skin. Most cases are caused by viral infections such as measles, rubella, roseola, dengue, hand, foot and mouth disease, and chickenpox. Less often the cause is bacterial, such as scarlet fever, and drug rashes can also come with a fever. What helps most in telling them apart is not the colour of the rash, but which day of the fever the rash appears, where it starts, and what it looks like
Most fevers with rash clear up on their own within 3–10 days, but a few diseases can become life-threatening within hours, such as meningococcemia or dengue in its critical phase. This article is arranged for both parents of a child with a fever and adults who have it themselves, covering what each disease looks like, whether it is contagious, how long it lasts, which medicines can ease it, and which signs mean you should not wait at home
What is fever with rash, and why does a fever come with a rash?
The rash in a fever with rash arises through 3 main mechanisms, which explain why the rash looks different in each disease
The germ reaches the skin directly: some viruses enter skin cells and cause blisters, such as chickenpox and hand, foot and mouth disease
The immune system reacts to the germ: small blood vessels in the skin widen and become inflamed, so the rash appears as red patches or red spots over the body, as in measles, roseola, and common viral rashes
Toxins from the germ or damage to blood vessels: for example the toxin of streptococcus in scarlet fever, or leaky blood vessels causing bleeding spots in dengue and meningococcemia
In practice, a doctor always asks in this order: how old are you, how many days of fever, did the rash appear while the fever was still present or after it went down, did it start on the face, trunk, or hands and feet, does it fade when pressed, are there blisters, are there mouth sores or red eyes, have you taken any new medicine in the past 2–8 weeks, and do people around you have the same illness
Quick check: which disease does your fever with rash match?
Use this list as a rough guide only, not as a diagnosis
High fever, cough, runny nose, and red eyes 3–4 days earlier, then a red rash starting at the hairline and behind the ears and spreading downward → measles
Low fever or no fever, a faint pink rash starting on the face and spreading over the whole body within 24 hours, swollen lymph nodes behind the ears → rubella
A child aged 6 months to 2 years with a high fever for 3–5 days, and the rash appears after the fever goes down on the trunk → roseola
A high persistent fever for 2–7 days, severe body aches, flushed face, tiny bleeding spots, or a red rash with white islands in between as the fever subsides → dengue
A mild fever, an itchy red rash, red eyes, or joint pain so severe that walking is difficult, after mosquito bites → Zika or chikungunya
Blisters on the palms, soles, and buttocks with mouth sores → hand, foot and mouth disease
Itchy clear blisters starting on the trunk, with several stages at the same time: new blisters, pus-filled blisters, and scabs → chickenpox
A sore throat and a fine red rash that feels rough like sandpaper, with a red bumpy tongue → scarlet fever
An itchy red rash over the body appearing 4–14 days after starting a new medicine → drug rash
A high fever with spots or bruises that do not fade when pressed and spread quickly, or a black scabbed sore like a cigarette burn → meningococcemia or scrub typhus, go to hospital immediately
1. Measles
What it looks like: A high fever of 39–40 °C with cough, runny nose, and red eyes for 2–4 days before the rash. There may be tiny white spots on the inside of the cheeks (Koplik spots). The rash is made of red patches that start at the hairline, behind the ears, and on the face, then spread down the trunk and limbs within 3 days. The patches merge into sheets, and the fever is usually highest on the day the rash appears. As the rash fades it leaves brown marks and fine peeling
Cause: The measles virus, spread by respiratory droplets and able to linger in the air for a long time. It is one of the most contagious diseases. Anyone who has never been vaccinated and shares a room with a patient has a very high chance of catching it. The incubation period is 10–14 days
Severity/urgency: Moderate to high, especially in young children, adults, pregnant women, and people with weak immunity. Complications include pneumonia, middle ear infection, diarrhea, and encephalitis. A person can spread the virus from 4 days before to 4 days after the rash appears
When to see a doctor: Everyone who may have measles should see a doctor to confirm it and report it for disease control, and should call ahead so they do not infect others in the waiting room. Go urgently if there is breathlessness, drowsiness, seizures, or inability to eat or drink
Treatment is symptomatic. The World Health Organization recommends that children with measles receive an age-appropriate dose of vitamin A on 2 consecutive days, for example 200,000 units for children aged 1 year and over, prescribed by a doctor. For more detail, read What is measles? How do measles and rubella differ?
2. Rubella (German measles)
What it looks like: A low fever or no fever, and a faint pink rash of small spots that starts on the face, spreads over the whole body within 24 hours, and fades within 3 days. The hallmark is swollen, tender lymph nodes behind the ears and at the back of the head. Adults, especially women, often have pain in the finger and wrist joints as well
Cause: The rubella virus, spread by respiratory droplets. The incubation period is 14–21 days. About half of infected people have no rash at all
Severity/urgency: Low for most people, but very high for pregnant women, because infection in the first trimester puts the baby at risk of birth defects of the heart, eyes, and ears
When to see a doctor: A pregnant woman who has a rash or has been near someone with a feverish rash must tell her obstetrician immediately for a blood test, even if she has no symptoms herself
3. Roseola (Roseola infantum)
What it looks like: A child aged 6 months to 2 years has a high fever of 39–40 °C for 3–5 days but does not look very ill for that level of fever. Once the fever drops, a pink-red rash of small spots appears on the trunk and neck. It is not itchy and clears by itself in 1–2 days
Cause: Human herpesvirus 6 and 7 (HHV-6, HHV-7). Most children have already been infected before the age of 3
Severity/urgency: Low. The rash is not dangerous. The real risk is during the high fever, because about 10–15% of children may have a febrile seizure
When to see a doctor: Every infant under 3 months with a fever of 38 °C or higher must see a doctor, as must a child of any age who has a seizure, is drowsy, is hard to wake, or has a fever longer than 5 days. A rash that appears after the fever drops in a child who is cheerful again can usually be managed at home
4. Dengue
What it looks like: A high persistent fever for 2–7 days, headache, pain behind the eyes, and severe muscle aches. The face and trunk are flushed early on, and there may be tiny bleeding spots on the arms and legs. Around day 3–6, as the fever subsides or after it subsides, an itchy red rash appears on the legs and arms, with patches of pale skin in between, like white islands in a red sea
Cause: The dengue virus, carried by Aedes mosquitoes. It occurs all year round in Thailand and is most common in the rainy season
Severity/urgency: High. The most dangerous time is when the fever starts to drop, the critical phase of 24–48 hours when shock from plasma leakage can occur. Many people wrongly think that a falling fever means recovery
When to see a doctor: Anyone with a high fever for 2 days or more in an area with Aedes mosquitoes should have a blood test, and should go to hospital immediately if there are warning signs: severe abdominal pain, persistent vomiting, bleeding from the gums or nose, black stools, drowsiness, restlessness, cold hands and feet, or no urination for more than 4–6 hours
Important prohibition: when dengue is suspected, do not take aspirin, ibuprofen, or NSAID anti-inflammatory drugs, because they increase the risk of bleeding. Use paracetamol only. To tell a dengue rash from other rashes, read What does a dengue rash look like, is it itchy, and how many days does it last?
5. Zika and Chikungunya
What it looks like: Zika usually causes a low fever, a red rash of spots and small raised bumps over the body, marked itching, red eyes without discharge, and mild joint pain. Chikungunya causes a sudden high fever with severe pain in the wrists, ankles, and fingers, so much that making a fist or walking is difficult. The red rash appears around day 2–5
Cause: Viruses carried by Aedes mosquitoes, the same mosquito as dengue. The Zika virus can also be passed through sex and from mother to the baby in the womb
Severity/urgency: Mostly mild, clearing within 5–7 days, but Zika in pregnancy can cause the baby to have a small head, and joint pain from chikungunya can last for weeks to months
When to see a doctor: Every pregnant woman with a feverish rash, and anyone who cannot tell whether it is dengue, because these three diseases come from the same mosquito and look very similar at first
6. Hand, foot and mouth disease
What it looks like: A low to moderate fever for 1–2 days, mouth pain so bad that the child refuses food, shallow sores in the mouth, on the tongue, and on the palate, together with red spots or oval blisters on the palms, soles, buttocks, and knees. They are rarely itchy
Cause: Enteroviruses such as coxsackievirus A16 and enterovirus 71. It is common in children under 5 years and spreads through saliva, fluid from the blisters, and stools. Adults who care for children can catch it too
Severity/urgency: Mostly mild, clearing within 7–10 days, but enterovirus 71 can cause encephalitis. Some people lose their nails 3–8 weeks after recovery, which is not dangerous
When to see a doctor: A child who cannot drink, passes little urine, or has nervous system symptoms such as frequent startling during sleep, drowsiness, repeated vomiting, limb weakness, or fast breathing must go to hospital immediately. Read more: Hand, foot and mouth disease: how to tell the blisters from herpes and chickenpox
7. Chickenpox
What it looks like: A low fever and tiredness for 1–2 days, then red bumps that turn into clear blisters on a red base, starting on the trunk and scalp and then spreading to the face and limbs. They are very itchy. The hallmark is having bumps in several stages at the same time: new red bumps, blisters, pus-filled blisters, and scabs
Cause: The varicella-zoster virus, spread by respiratory droplets and fluid from the blisters. The incubation period is 10–21 days. The same virus hides in nerve ganglia and may return later as shingles
Severity/urgency: Most children recover within 7–10 days, but adults, teenagers, pregnant women, and people with weak immunity are more likely to get pneumonia or a secondary bacterial skin infection. A person can spread it from 1–2 days before the rash until every blister has scabbed over
When to see a doctor: Adults and teenagers aged 13 and over should see a doctor within the first 24 hours of the rash, because the antiviral drug acyclovir works best when started in this window. A commonly used adult dose is 800 mg 5 times a day for 7 days. Go to hospital if the blisters are swollen, red, hot, or very pus-filled, or if there is breathlessness or drowsiness. Read more: Chickenpox: causes, symptoms, and treatment
8. Scarlet fever
What it looks like: A child aged 5–15 years has a fever, a very sore throat, and red swollen tonsils. Within 1–2 days a fine red rash of tiny spots appears that feels rough like sandpaper, starting on the neck, armpits, and groin and then spreading over the body. The skin folds have dark red lines, the face is flushed but the area around the mouth is pale, and the tongue is red and bumpy like a strawberry. 1–2 weeks later the skin on the fingertips and toes peels
Cause: Group A Streptococcus bacteria that produce a toxin which causes the rash
Severity/urgency: Moderate. Unlike most fevers with rash, it needs antibiotics to prevent rheumatic fever and kidney inflammation. A commonly used drug is amoxicillin 50 mg/kg/day (not more than 1,000 mg/day) or penicillin V, taken for the full 10 days even if the fever goes down by day 2
When to see a doctor: A child with a sore throat and a rough rash over the body should see a doctor to have the throat examined. The child can return to school after 24 hours of taking the medicine and having no fever
9. Drug rash with fever (Drug exanthem)
What it looks like: A red rash of small spots and patches similar to a measles rash, markedly itchy, starting on the trunk and spreading to the limbs, appearing 4–14 days after starting a new medicine. There may be a low fever as well. Common culprits are penicillin-group antibiotics and sulfa drugs, anti-seizure drugs, and allopurinol. The rash usually fades within 1–2 weeks after stopping the drug
Cause: A reaction of white blood cells to the drug, not an infection, so it is not contagious. A common source of confusion is a child or teenager with a sore throat from EBV virus who is given amoxicillin and develops a red rash over the body, which a doctor must sort out
Severity/urgency: Mostly mild, but it must be told apart from two severe drug reactions: Stevens-Johnson syndrome (SJS), with sores in the mouth, eyes, or genitals, blistering or peeling skin, and painful skin, and DRESS, which appears 2–8 weeks after starting a drug with facial swelling, high fever, swollen lymph nodes, and hepatitis
When to see a doctor: Whenever a rash covers the body after starting a new medicine, see a doctor before stopping the drug yourself, especially medicine for a chronic condition, and go to the emergency room immediately if there are sores on the mucous membranes or blistering skin. Read more: Drug exanthem: how to tell it from SJS
10. Fever with bruise-like spots or a cigarette-burn sore: meningococcemia and scrub typhus
What it looks like: Meningococcemia begins with a sudden high fever, body aches, and cold hands and feet, then purple spots or bruises that do not fade when pressed and spread within a few hours. Scrub typhus has a high fever, severe headache, a red rash on the trunk, and often a black scabbed sore with a red border, 5–10 mm across, like a cigarette burn, in warm hidden areas such as the groin, armpits, or waistband
Cause: Meningococcemia is caused by the bacterium Neisseria meningitidis. Scrub typhus is caused by rickettsia bacteria spread by mite larvae in forests, orchards, or farmland
Severity/urgency: The highest in this article. Meningococcemia can cause shock and death within 24 hours. Scrub typhus responds well to doxycycline 100 mg twice a day for about 7 days, but late diagnosis can lead to lung and liver failure
When to see a doctor: A fever with bleeding spots that do not fade when pressed means going to the emergency room immediately, without waiting to see how it goes. A simple test is to press a clear glass onto the rash: if the rash is still red or purple when seen through the glass, it is a bleeding spot. Read more about telling them apart at What causes bleeding spots under the skin?
When the rash appears in relation to the fever helps tell diseases apart the most
If you remember only one thing, remember when the rash appears compared with the fever
Rash appears with the first days of fever: rubella, Zika, chickenpox, hand, foot and mouth disease, and scarlet fever (within 1–2 days)
Rash appears on day 3–5 while the fever is still high: measles, chikungunya, scrub typhus
Rash appears as the fever goes down: roseola in young children, and the recovery-phase rash of dengue
Rash appears 4–14 days after starting a medicine: drug rash (if it is 2–8 weeks and the face is swollen, think of DRESS)
Bleeding-spot rash that spreads within hours: meningococcemia, go to hospital immediately
Where the rash starts also helps. Measles starts at the hairline and behind the ears, rubella starts on the face, roseola and chickenpox start on the trunk, scarlet fever starts on the neck and skin folds, hand, foot and mouth disease appears on the palms, soles, and buttocks, and the recovery-phase dengue rash is usually most obvious on the legs
“Weak immunity, rash appears”: what causes it?
“Weak immunity, rash appears” is not a formal medical diagnosis, but people use it for a rash that appears when they are ill, sleep-deprived, or stressed. In reality it is usually one of the following conditions
Common viral rash (viral exanthem): A red rash of small spots over the body that appears during or after a cold, flu, or COVID. It is rarely itchy, clears on its own within 3–7 days, and is the most common
Hives from an infection: Itchy raised red patches that move around, each lasting no more than 24 hours. Common in children with a cold or urinary tract infection. Read more: What causes hives?
Herpes or shingles flare-up: Grouped blisters with a burning pain along one side following a nerve. This one really does relate to lowered immunity, and you should see a doctor within 72 hours to get an antiviral drug
Rash from early HIV infection: A fever, sore throat, and red rash over the body 2–4 weeks after a risk exposure. A blood test is advised. Read more: What does an HIV rash look like?
If a rash keeps coming back every time you are ill, you have repeated shingles or oral thrush, or you lose weight without knowing why, have a doctor assess your immunity rather than concluding it is just weak immunity
How does fever with rash in adults differ from children?
Children usually have viral fevers with rash that clear on their own, such as roseola and hand, foot and mouth disease. In adults with a fever and rash, doctors think of a different group of diseases
Dengue, Zika, and chikungunya: The most common in Thai adults, and adults who have had dengue before are at risk of severe disease when infected again with a different serotype
Drug rash: Adults take more medicines than children, so a rash after starting a new drug must always be considered
Chickenpox and measles in adults: Clearly more severe than in children, with a higher risk of pneumonia
Sexually transmitted infections: The rash of early HIV, and secondary syphilis, which often has a rash on the palms and soles
Scrub typhus and leptospirosis: In people who hike in forests, garden, or wade through floodwater
Adults with a fever and rash should therefore see a doctor sooner than a cheerful child, especially if the fever lasts more than 2–3 days or a new medicine was just started
Is fever with rash contagious, and how many days off school or work?
Most infectious fevers with rash are contagious, except drug rashes and mosquito-borne fevers, which do not pass directly from person to person (except Zika by sex). The general guidance in use is
Measles: Stay isolated until 4 days after the rash appears
Rubella: Stay isolated for 7 days after the rash appears, and avoid pregnant women
Chickenpox: Stay isolated until every blister has scabbed over, usually about 5–7 days
Hand, foot and mouth disease: Stay off school for about 7 days, or until the mouth sores heal and there is no fever. The virus can still pass in stools for several weeks, so wash hands after changing diapers
Scarlet fever: Stay off school until 24 hours after finishing the antibiotics dose and having no fever
Dengue, Zika, chikungunya: Not spread by touch, but the patient should sleep under a mosquito net or avoid mosquito bites, so mosquitoes do not carry the virus to others at home
How many days until fever with rash goes away?
The duration depends on the disease. The following figures are approximate for healthy people
Roseola: fever 3–5 days, rash clears in 1–2 days
Rubella: rash clears in 3 days
Measles: rash lasts about 5–7 days and can leave brown marks for another 1–2 weeks
Dengue: fever 2–7 days, the recovery-phase rash can itch for another 3–7 days
Hand, foot and mouth disease and chickenpox: 7–10 days
Scarlet fever: fever goes down within 24–48 hours of starting the drug, and skin peels 1–2 weeks later
Drug rash: fades within 1–2 weeks after stopping the drug causing the allergy
If the fever has not gone down after more than 5 days, or the rash keeps spreading after 7 days, go back to the doctor again, even if you have already been examined
How is fever with rash treated, and which medicines can ease it?
Most viral fevers with rash have no medicine that kills the virus directly, so treatment means controlling the fever, easing the itch, and preventing dehydration, except for a few diseases that need specific medicines from a doctor: scarlet fever (antibiotics), chickenpox in adults (antiviral drug), scrub typhus (doxycycline), and measles in children (vitamin A)
Fever medicine: Paracetamol is the main choice. In children, use 10–15 mg/kg per dose, at least 4–6 hours apart, no more than 5 times a day. In adults, 500–1,000 mg per dose, no more than 4,000 mg/day, and no more than 2,000–3,000 mg/day for people who drink alcohol regularly or have liver disease. Fever medicine makes you more comfortable but does not make the disease go away faster
Medicines not to use on your own: Do not give aspirin to children and teenagers with a fever, because of the risk of Reye syndrome, especially in chickenpox, and avoid ibuprofen and all NSAID painkillers until a doctor has ruled out dengue
Itch relief: Antihistamines such as cetirizine, 10 mg once a day for adults and 2.5 mg twice a day for children aged 2–5 years, or chlorpheniramine, 4 mg every 6 hours as needed for adults, which cause drowsiness. Avoid antihistamines in children under 2 years without asking a doctor. Apply calamine lotion on the rash or on chickenpox blisters that have not broken, and take a warm bath or sponge the body with room-temperature water
What not to apply: Steroid creams on a rash of unknown cause, especially on blisters, and medicated balms or herbal remedies on broken blisters, which irritate the skin and risk a repeat infection
The choice of medicine, the dose, and the length of use are decisions for a doctor, based on weight, age, underlying conditions, and the actual disease
How to care for yourself at home with a fever and rash
Drink enough fluids: Watch for urine every 4–6 hours and a colour that is not dark. For a child with mouth pain from hand, foot and mouth disease, give milk or cold water and soft, non-spicy food
Take the temperature and keep a record: Write down the temperature, the times medicine was given, and the day the rash appeared. Taking a photo of the rash every day helps the doctor diagnose much faster
Keep nails short and do not scratch the blisters: This reduces repeat bacterial infection and scarring, especially in chickenpox
Separate belongings and wash hands: Do not share cups, towels, or spoons. Wash hands with soap for at least 20 seconds
Prevent mosquito bites: If dengue, Zika, or chikungunya is suspected, sleep under a net and apply mosquito repellent throughout the fever
Note the medicines you take: Every one, including supplements and herbal products in the past 2 months, so the doctor can assess for a drug rash
How does a doctor diagnose fever with rash?
Most of the time a doctor can diagnose it from the history and physical examination, looking at the rash pattern, location, blisters, bleeding spots, mouth sores, and lymph nodes, and examining the throat. Further tests are chosen according to the suspected disease, such as
A complete blood count, platelets, and hematocrit for dengue
NS1 antigen or antibody tests for dengue, Zika, or measles virus
A throat swab for streptococcus in a child with suspected scarlet fever
Liver function, kidney function, and eosinophil white cell count in anyone with suspected DRESS
A skin biopsy when the rash does not clearly fit any disease, or when a severe drug rash or vasculitis is suspected
A dermatologist can help most when the rash is still there after the fever has gone, when there is a chronic itchy rash after an infection, or when it is unclear whether it is a viral rash or a drug rash
Danger signs that mean going to hospital immediately
Spots or bruises that do not fade when pressed, especially if they spread quickly or come with a high fever
An infant under 3 months with a fever of 38 °C or higher
Drowsiness, hard to wake, confusion, seizures, stiff neck, or limb weakness
Breathlessness, fast breathing, or blue lips
Severe abdominal pain, persistent vomiting, bleeding from the gums or nose, or black stools, especially when the fever goes down
No urination for more than 4–6 hours, very dry mouth, or cold hands and feet
Mouth sores, red inflamed eyes, blistering skin, or peeling skin after starting a new medicine
A high fever lasting more than 5 days, or any pregnant woman with a feverish rash
People with weak immunity, such as those receiving chemotherapy, immunosuppressants, or high-dose steroids
Common myths about fever with rash
“Once the fever goes down and the rash appears, you have recovered” This holds for roseola in young children, but in dengue the time the fever goes down is the most dangerous time
“Once the rash comes out the fever will go down, so you must let the rash come out fully” The belief in “bringing the rash out” by wrapping up in thick blankets or skipping baths has no evidence and makes the fever higher. Sponging and a warm bath are fine as usual
“Do not eat eggs or foods that make it worse” There is no evidence that they make the rash worse. Patients should get enough protein, except people who truly have an allergy to that food
“If you have had chickenpox or measles, you do not need the vaccine again” True only for a disease you definitely had, but many rashes look alike, so if you are unsure, have your immunity tested or get vaccinated as your doctor advises
Preventing fever with rash
The measles, mumps, rubella (MMR) vaccine, 2 doses, under the Thai childhood vaccine schedule at 9 months and 1 and a half years. Adults who never received it or are unsure can ask a doctor, and women should avoid pregnancy for 1 month after the shot
The chickenpox vaccine, 2 doses, for children and adults who have never had the disease
The dengue vaccine for groups a doctor recommends, and clearing standing water around the home every 7 days
Wash hands, do not share personal items, and keep sick children off school for the contagious period
Tell the doctor every time if you have had a drug allergy, and carry a drug allergy card
Short summary
Most fevers with rash are caused by viruses and clear on their own in 3–10 days, but you must first rule out diseases that need specific medicine or can be life-threatening
The day the rash appears compared with the fever is the key clue: a rash after the fever drops in a young child is usually roseola, but in an adult with a high persistent fever, think of dengue
Bleeding-spot rash that does not fade when pressed, together with fever, means going to the emergency room immediately
Use paracetamol for fever, avoid aspirin in children, and avoid ibuprofen until dengue has been ruled out
A rash over the body 4–14 days after starting a new medicine may be a drug rash, and if there are mouth sores or blistering skin it is an emergency
A pregnant woman with a feverish rash, or who has been near someone with one, should tell her obstetrician immediately
Frequently asked questions about fever with rash
Fever with rash in adults: what are the symptoms?
Adults usually have a fever of 38–40 °C, body aches, and headache, then a red rash of spots or patches on the trunk and limbs. Some diseases itch a lot, such as Zika and the recovery-phase rash of dengue, some cause severe joint pain, such as chikungunya, and some have blisters, such as chickenpox. In Thai adults, the causes to think of first are dengue, a drug rash from a newly started medicine, and chickenpox or measles in people who were never vaccinated. Adults with a fever and rash lasting more than 2–3 days should therefore see a doctor for a blood test instead of waiting for it to pass
How many days until fever with rash goes away?
Most clear within 3–10 days, depending on the disease. In roseola in young children the rash clears 1–2 days after the fever goes down, rubella clears in 3 days, measles takes 5–7 days, and hand, foot and mouth disease and chickenpox take about 7–10 days. Dengue has a fever for 2–7 days, and the recovery-phase rash may itch for about another week. A drug rash fades within 1–2 weeks after stopping the drug causing the allergy. If the fever has not gone down after 5 days, or the rash is still spreading after 7 days, go back to the doctor, even if you have already been examined
Is fever with rash in adults contagious?
It depends on the cause. Measles, rubella, chickenpox, and hand, foot and mouth disease pass from person to person by respiratory droplets or touch. Adults should therefore keep away from young children, older people, and pregnant women during the contagious period, for example until 4 days after the rash appears for measles, and until all the blisters have scabbed over for chickenpox. Dengue and chikungunya do not pass by touch, but a mosquito that bites a patient can carry the virus to others. A drug rash is not contagious at all
Fever with rash in adults: how is it treated?
Most is treated by symptoms: paracetamol 500–1,000 mg per dose, 4–6 hours apart, no more than 4,000 mg a day, drinking enough to urinate every 4–6 hours, and an antihistamine such as cetirizine 10 mg once a day with calamine lotion if itchy. Avoid ibuprofen and aspirin until a doctor has ruled out dengue. Some diseases need specific medicines, such as acyclovir for chickenpox in adults, started within the first 24 hours, or antibiotics for scarlet fever and scrub typhus. The choice of medicine should be a doctor’s after an examination
“Weak immunity, rash appears”: what causes it?
Most often it is a common viral rash that appears during or after a cold or flu. The rash is small red spots over the body, rarely itchy, clearing on its own in 3–7 days. Next most common is hives from an infection, which are itchy raised patches, each lasting no more than 24 hours. The condition that really relates to lowered immunity is a herpes or shingles flare-up, with grouped blisters and burning pain, and an antiviral drug should be started within 72 hours. If the rash keeps coming back, there is thrush in the mouth, or weight loss, have a doctor look for the cause
Rash appeared after the fever went down: is it dangerous?
In a child aged 6 months to 2 years with a high fever for 3–5 days, if the rash appears as the fever goes down and the child is cheerful again and eating, it is usually roseola, which is not dangerous and clears in 1–2 days. But in an older child or adult who has had a high persistent fever, the time the fever goes down may be the critical phase of dengue. If there is abdominal pain, persistent vomiting, drowsiness, cold hands and feet, bleeding from the gums, or bleeding spots that do not fade when pressed, go to hospital immediately, even if the fever has gone down
If the rash is blistering or appeared after starting a new medicine, read on at Chickenpox and Drug exanthem. For a rash that may be dengue, see What does a dengue rash look like, and for other skin disease articles see All skin disease articles
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed October 29, 2026
The information in this article is general knowledge, not a diagnosis or a personal prescription. Many fevers with rash look alike in the early stages and must be examined by a doctor. The choice of medicine, the dose, and the length of treatment are the doctor’s decision. Results vary from person to person.
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