An exanthem is the medical term for a widespread rash often accompanied by symptoms like fever or headache. The word originates from the Greek “exanthema,” meaning “a breaking out.” These rashes are a reaction to an infection, most commonly viral, but can also be caused by bacteria. The rash is a visible sign of the body’s immune system responding to an organism.
The Six Classic Childhood Exanthems
Historically, as physicians began to differentiate common childhood illnesses, they assigned numbers to the widespread rashes they observed. This resulted in a list of six “classic” exanthems, each with a distinct cause. While some are now rare due to vaccination, they provide a foundation for recognizing rash-producing illnesses.
First disease is measles (rubeola), caused by the measles virus. Before the rash, a child experiences a prodrome, or initial symptoms, including fever, cough, runny nose, and conjunctivitis. An indicator is the appearance of Koplik spots—small, white spots inside the cheek—a day or two before the main rash. The exanthem is a reddish-brown rash that begins on the hairline and face, then spreads downwards.
Second disease, or scarlet fever, is caused by the bacterium Streptococcus pyogenes, which also causes strep throat. The prodromal phase includes a sore throat, fever, and headache. The rash emerges 12 to 48 hours later as tiny red bumps that feel like sandpaper, starting on the neck and chest before spreading, often sparing the palms and soles.
Third disease is rubella, also known as German measles. Caused by the rubella virus, it is milder than measles. The prodrome in children can be minimal, but adolescents and adults may have a low-grade fever and swollen lymph nodes. The rash consists of pink spots that start on the face and spread downward, clearing in the same order within about three days.
Fourth disease, once called Dukes’ disease, is no longer a distinct medical diagnosis. The term has fallen out of use, as cases were likely atypical presentations of scarlet fever or other known viral rashes.
Fifth disease, erythema infectiosum, is caused by parvovirus B19. It begins with mild, cold-like symptoms like a low-grade fever and runny nose. After these symptoms fade, a rash appears with bright red cheeks, giving it the name “slapped cheek” disease. A lacy, net-like rash then emerges on the trunk, arms, and legs, which may reappear with exposure to sunlight or heat.
Sixth disease, or roseola infantum, is caused by human herpesvirus 6 (HHV-6) and affects children between six months and two years old. The illness begins with a sudden, high fever lasting three to five days, while the child often appears well. Once the fever breaks, a rash of small, pink spots appears, starting on the trunk before spreading to the neck and arms.
Other Prevalent Exanthematous Illnesses
One of the most well-known is chickenpox, caused by the varicella-zoster virus. In children, the rash is often the first sign, though adults may experience a day of fever beforehand. The rash progresses through stages, beginning as small red spots that develop into fluid-filled blisters, or vesicles. These intensely itchy vesicles eventually cloud over, burst, and form scabs, with spots in all stages of development present simultaneously.
Hand, Foot, and Mouth Disease (HFMD) is most frequently caused by the coxsackievirus. It starts with a low-grade fever, sore throat, and a feeling of being unwell. A day or two later, painful sores develop in the mouth, followed by a non-itchy skin rash with flat or raised red spots on the palms and soles. The rash may also appear on the buttocks and genitals.
The Diagnostic Approach
Determining the cause of an exanthem involves a methodical clinical evaluation. A healthcare provider will start with a patient history, gathering details about vaccination status, recent travel, and known exposures to sick individuals. The nature of the prodrome—the symptoms that appear before the rash—is also an important clue.
A physical examination of the rash provides direct evidence. The provider assesses the appearance of the lesions—whether they are flat spots, raised bumps, or fluid-filled vesicles. The distribution and spread of the rash are also noted, as a rash starting on the face suggests different illnesses than one concentrated on the hands and feet.
General Management and Warning Signs
For most viral exanthems, treatment is supportive, as the illnesses are self-limiting. The focus is on keeping the child comfortable by ensuring they drink plenty of fluids and get adequate rest. Fever can be managed with acetaminophen or ibuprofen, but aspirin should be avoided in children due to its link with Reye syndrome. For itchy rashes, cool baths or calamine lotion can provide relief.
While most childhood exanthems are not dangerous, certain warning signs require immediate medical consultation. A rash that appears as purple or blood-colored spots or does not fade with pressure could signal a serious condition. You should also seek urgent medical attention for any of the following:
- A high fever that is persistent or does not respond to medication.
- Any difficulty breathing or a severe headache with a stiff neck.
- Extreme lethargy and unresponsiveness.
- Signs of dehydration, such as a dry mouth, crying without tears, or decreased urination.