Exanthem is a widespread rash that commonly accompanies a viral infection but can also be caused by other conditions, whether infectious or non-infectious. You may see the rash as spots, blotches, or bumps which may or may not be itchy. Exanthem usually occurs with other systemic flu-like symptoms such as fever, headache, and feeling unwell. While some of these rashes may seem nonspecific, certain exanthems are unique in distribution and morphology that can help differentiate the type of virus that causes it. Additionally, some exanthems are more common in specific age groups, which can help investigate the rash and establish a diagnosis.¹

What are the causes of viral exanthem? 

A wide range of viral infections can cause exanthem at any age. Some of them have distinct rash characteristics that can be valuable in distinguishing the cause. Below are the common causes based on the type of causative virus and how the rash might appear:

Roseola infantum

• Caused by human herpes virus type 6B (HHV-6B) and possibly type 7 (HHV-7)
• Usually affects children between six and twelve months of age. Most cases happen in children younger than 2 years old
• Maculopapular rash ( small pink-red flat areas and raised bumps) that starts on the trunk, spreads to the neck and arms and can appear mildly on the face and legs^2,3

Hand foot and mouth disease (HFMD)

• Caused by Coxsackie A16, A10 and the echovirus
• It usually affects infants and children, but can also affect adults
• The rash can involve the hands, feet, mouth, and sometimes the genitals and buttocks
• The rash may present as grey elliptical spots, bumps, or blisters which may be painful or not
• Typically, there are prodromal symptoms that appear 12-36 hours before the rash, including low-grade fever, cough, loss of appetite, abdominal pain, and sore mouth or throat^3,4

Erythema infectiosum (slapped cheek syndrome)

• Caused by Parvovirus B19 is transmitted via respiratory droplets
• Symptoms may include high temperature, headache, and runny nose
• The rash appears in two stages: At first, there are red, swollen patches on the cheeks, but the nose and eyes are usually spared. This stage lasts 1-4 days. In the second stage, the rash spreads to the trunk, arms, and legs. Some parts of the rash may start to fade, creating a net-like pattern. It might be itchy and lasts five to nine days, but the rash can come back for weeks to months with triggers like sunlight, stress, exercise, and temperature changes

Varicella (chickenpox)

• Caused by the varicella-zoster virus, most commonly in children under 10 years old but can affect any age
• Small red, pink, or skin-coloured spots can appear anywhere on the body. These spots can turn into itchy blisters. Eventually, they form scabs or crusts, with some scabs leaking fluid and others becoming flaky
• Symptoms may include fever, loss of appetite, and feeling unwell⁵

Measles (Rubeola)

• Caused by morbillivirus subtype of the Paramyxovirus family, it spreads through airborne or droplet transmission
• Symptoms typically begin with high temperature, cough, and red eyes (conjunctivitis). In older children, there may also be sensitivity to light (photophobia)
• The rash starts as small red spots on the face, then spreads to the chest and abdomen, and eventually to the arms and legs
• Before the rash appears, small red spots with bluish-white centres, known as Koplik’s spots, may appear on the mucous membranes of the mouth 1-2 days prior^2,6

Rubella (German measles or 3-day measles)

• Caused by the rubella virus, typically affects children and non-immune young adults. If contracted by a pregnant woman, it can lead to severe birth defects known as congenital rubella syndrome
• Symptoms, which may appear 1-5 days before the rash, include mild fever, headache, general malaise, sore throat, and swollen lymph glands
• The rash, characterised by pink or light red patches, first appears on the face and neck before spreading to the trunk and limbs^3,7

Shingles (Herpes zoster)

• Typically seen in adults or the elderly
• Caused by the reactivation of the varicella-zoster virus that has been dormant in the nervous system
• Symptoms include pain followed by a rash that develops into itchy blisters. The rash typically appears on one side of the body, affecting the area of the skin innervated by the affected nerve.
• Usually, before the rash appears, you may feel a headache, fever, and burning/itching/numb sensation on the affected skin

Pityriasis rosea

• Most commonly seen in teenagers or young adults, but can affect people of any age, with a higher occurrence in women. Associated with viral, bacterial, or non-infective causes
• The rash begins as a single oval or round spot on the trunk and gradually spreads to other parts of the body. These lesions are smaller and become scaly. Typically, the rash appears symmetrically on both sides of the body, resembling a Christmas tree pattern
• Some individuals may experience flu-like symptoms a few days before the rash appears⁹

Gianotti-Crosti syndrome (papular acrodermatitis of childhood)

• Often associated with viral infections, mainly the Epstein–Barr virus or hepatitis B virus, and typically affects children under 5 years old
• Symptoms include small skin-coloured bumps or red bumps and blisters on the legs, buttocks, arms, and face. These are often preceded by flu-like symptoms such as fever, sore throat, and general malaise¹⁰

Unilateral laterothoracic exanthem

• A relatively uncommon condition primarily affects one side of the body in young children
• It starts as tiny raised pink bumps, which then become flat and scaly over the following week. The rash typically begins around the armpit or groin and gradually spreads to the face, genital area, hands, and feet
• Often accompanied by fever, sore throat, vomiting, cold symptoms, and diarrhoea¹¹

When should I worry and seek medical attention?

Most exanthem caused by viral infection are harmless and can go away on their own (self-limiting). However, if you or your child start developing these symptoms, you should seek medical help.

• Struggle to breathe due to swollen lips or tongue
• Confused or lethargic(extremely weak)
• Become pale, mottled, or very cold
• Extremely agitated
• Rash that doesn’t fade with pressure
• Develop a painful or blistering rash
• The rash affects more than 90% of the body
• Develops red lips/tongues
• Significant skin peeling
• If your baby is under 3 months old and has a rash and fever
• Continue to have a fever (38 degrees or above) for more than 5 days¹²

FAQ’s

What does a viral rash look like?

Viral rash may vary in size, shape, and colour. Here are some common characteristic

• Colour: pink or red spots, sometimes darker skin tone or skin colour
• Shape: can be flat (macules), slightly raised (papules), or blister (vesicles)
• Distribution: may start in one area and spread to other parts of the body, or just in a localized areaThis feature usually helps to identify the cause
• Itchiness: may or may not be itchy
• Size: can be varied

Most of the exanthem will be preceded by prodromal symptoms that occur a few days before the rash appears. These symptoms include fever, headache, sore throat, feeling tired and unwell, and sometimes cough or runny nose. In some types of viral infection, these symptoms may appear at the same time as the rash.¹³

Is viral exanthem serious?

In most cases, viral infections are self-limiting, meaning they can resolve on their own within a few days or weeks after infection. However, serious complications can occur in rare cases, particularly among certain groups such as infants, the elderly, pregnant individuals, or those with weakened immune systems. For example, chickenpox can lead to secondary bacterial infections. It's important to recognize signs of complications and seek medical help when necessary.

How long does a viral exanthem last?

Typically the rash will resolve within days or a few weeks. 

Where do viral rashes start?

It depends on the type of virus that causes it. For example, in measles, the rash typically starts behind the ears or on the face before spreading to the body. In chickenpox, the rash may first appear on the face and trunk. In hand, foot, and mouth disease (HFMD), the rash initially appears in the mouth, followed by lesions on the hands and feet.^4,14

Summary

Viral exanthem is a rash that may manifest as spots, blotches, or bumps caused by viral infections, occurring across all age groups. This rash typically emerges alongside or before flu-like symptoms such as fever, headache, malaise, cough, or runny nose. Generally, viral infections are self-limiting, resolving within days or weeks without complications. The way the rash looks in different diseases can help figure out which virus caused it. Some common causes of viral rashes include:

• Roseola infantum
• Hand, foot, and mouth disease
• Erythema infectiosum
• Varicella (chickenpox)
• Measles
• Rubella
• Shingles
• Pityriasis rosea
• Gianotti-Crosti syndrome
• Unilateral later thoracic exanthem

While viral exanthems are typically not concerning, it's good to keep an eye out for any signs of problems and know when to see a doctor if needed.