Viral Exanthem (Viral Rash)

What a viral exanthem is

Exanthem means a rash that breaks out across the skin. A viral exanthem is the skin's reaction to a virus spreading through the body. The rash is caused either by the virus directly infecting skin cells or by the immune system reacting to it.

Most viral exanthems are nonspecific: doctors know a virus is responsible but cannot tell which one, and testing does not change treatment. A few viruses cause rashes with a recognizable pattern, called the classic childhood exanthems.

Viral exanthem symptoms

• The rash: flat or slightly raised pink or red spots (maculopapular), often blending into blotches. It usually starts on the chest, belly or back and spreads to the arms, legs and sometimes the face.
• Blanching: the spots fade when you press on them.
• Itch: usually mild or absent.
• Fever: often comes before the rash, or with it.
• Cold-like symptoms: runny nose, cough, sore throat, red eyes.
• Tummy upset: diarrhea or vomiting with some viruses, such as enteroviruses.
• Swollen glands in the neck.
• Feeling tired and irritable, but a child with a typical viral rash is usually not very sick.

A mild viral exanthem is a light, patchy rash in a child who is otherwise well. It needs no treatment and fades within a few days.

Common causes and classic types

COVID-19, dengue, Zika, HIV seroconversion and hepatitis B can also cause rashes, mainly in adults.

Rashes that look viral but are not

Some serious conditions start with a rash that resembles a viral exanthem:

• Meningococcal disease: a rash that does not blanch, with fever and rapid illness. An emergency.
• Scarlet fever: a bacterial (strep) infection with a sandpaper-like rash, sore throat and a "strawberry" tongue. It needs antibiotics.
• Kawasaki disease: prolonged fever, red eyes, red lips and swollen hands. It needs hospital treatment to protect the heart.
• Drug eruptions: a rash starting 4 to 14 days after a new medicine, often antibiotics or anticonvulsants.
• Pityriasis rosea: a single large "herald patch" followed by oval patches in a Christmas tree pattern on the back.

Viral exanthem in adults

Adults get viral rashes less often than children, but parvovirus B19 often causes joint pain and a faint rash in adults, and acute HIV, hepatitis B, mononucleosis, measles and COVID-19 can cause rashes. A new rash with fever in an adult should be checked by a doctor, especially after travel, a new sexual partner or contact with someone with measles. Pregnant women exposed to rubella, parvovirus, chickenpox or measles should contact their prenatal clinic, because these infections can affect the baby.

How it is diagnosed

Diagnosis is usually clinical. The doctor will ask when the fever and rash began, where the rash started, whether it itches, about vaccinations, recent medicines, travel and sick contacts, and will look at the skin, mouth, eyes and glands. The "glass test" or pressing on the rash checks whether it blanches.

Tests are needed only when the result changes care: for example, a swab or blood test for measles, rubella or parvovirus in pregnancy or during an outbreak, a strep test for suspected scarlet fever, or blood tests in a very sick child.

Treatment and home care

There is no specific treatment for most viral exanthems. The rash clears as the immune system controls the virus.

• Fever and discomfort: acetaminophen (paracetamol) or ibuprofen at the label dose for age or weight. Do not give aspirin to children or teenagers, because of the risk of Reye's syndrome.
• Fluids: offer frequent small drinks, breast milk or formula.
• Itch: lukewarm baths, loose cotton clothing, fragrance-free moisturizer, and calamine lotion for chickenpox. An oral antihistamine can help older children sleep.
• Rest at home until the fever has gone.
• Antivirals are used only in specific cases, such as chickenpox in adults or people with weak immune systems.
• Antibiotics do not help viral rashes.

Is it contagious?

The virus behind the rash is usually contagious, though often most so before the rash appears. Children with roseola or fifth disease are usually no longer contagious once the rash is out. Chickenpox is contagious until all the spots have crusted. Measles is contagious from 4 days before to 4 days after the rash appears. Ask your doctor or local guidance about returning to school or childcare.

How long does a viral rash last?

Most viral exanthems fade within 3 to 7 days. Chickenpox spots crust within about a week. The lacy rash of fifth disease can come and go for several weeks, flaring with heat, sunlight or exercise. A "chronic viral exanthem" is not a recognized diagnosis: a rash lasting more than 2 weeks is unlikely to be a simple viral rash and should be reviewed for other causes such as eczema, a drug reaction, urticaria or pityriasis rosea.

Prevention

• Vaccination prevents measles, rubella and chickenpox (MMR and varicella vaccines).
• Wash hands frequently and avoid sharing cups and utensils during illness.
• Keep children with fever at home.

Frequently asked questions

What are the symptoms of a viral exanthem?

The main symptom is a widespread pink or red rash of flat or slightly raised spots, usually starting on the trunk. It often follows or comes with fever, runny nose, cough, sore throat, red eyes or diarrhea. The spots usually fade when pressed and are only mildly itchy, if at all.

How long does a viral exanthem last?

Most viral rashes fade within 3 to 7 days without treatment. Some, such as the rash of fifth disease, can come and go for a few weeks. A rash that lasts more than 2 weeks, keeps returning or gets worse should be checked by a doctor for other causes.

Is a viral exanthem contagious?

The virus causing it usually is. Spread is often greatest before the rash appears, when cold-like symptoms or fever are present. By the time the rash shows, some infections, such as roseola and fifth disease, are no longer contagious. Chickenpox and measles remain contagious after the rash appears.

How do you tell a viral rash from a serious rash?

A typical viral rash blanches when pressed, and the child is generally well. A rash of purple or red spots that do not fade under a pressed glass, a floppy or very drowsy child, breathing difficulty, or fever lasting 5 days or more needs urgent medical care.

Can adults get a viral exanthem?

Yes, though less often than children. Parvovirus B19, mononucleosis, acute HIV, hepatitis B, measles and COVID-19 can all cause rashes in adults. Adults with a new rash and fever should see a doctor, and pregnant women should report any rash or exposure to a rash illness.