Scarlet fever is an acute toxin-mediated disease caused by infection with group A beta-hemolytic streptococci (Streptococcus pyogenes). Most cases follow a streptococcal pharyngitis or tonsillitis. However, streptococcal sepsis, cellulitis, puerperal infection, or surgical infection can initiate scarlet fever. Scarlet fever is most common in children younger than 10 years, but it can affect adults as well.

A 2-5 day incubation period precedes the onset of rash. Associated prodromal symptoms include fever and malaise. Sore throat and swollen, tender anterior cervical lymph nodes are typical. Abdominal pain, nausea, and vomiting are common in younger children. Petechiae may be present on the soft palate.

The characteristic rash begins within 12-48 hours of fever onset. It initially presents on the trunk and spreads to involve the extremities, sparing the palms and soles. The rash is often accentuated in flexural creases. It manifests as confluent tiny, erythematous papules with a "sandpaper-like" appearance. Enlarged tongue papillae may give the appearance of a "strawberry tongue." The rash tends to fade in a week and is followed by desquamation.

Once a fatal disease in the pre-antibiotic era, scarlet fever's associated complications are now fortunately rare with the existence of effective antibiotic therapy. However, meningitis, otitis, sinusitis, pneumonia, arthritis, rheumatic fever, and glomerulonephritis can still rarely occur as in any streptococcal infection.

In 2022-2023, the United Kingdom reported a surge in scarlet fever that coincided with an increase in invasive S pyogenes (invasive group A strep [iGAS]) infections. In the United States and elsewhere in Europe, iGAS infections in children, including necrotizing fasciitis and streptococcal toxic shock syndrome, have increased without a concomitant increase in cases of scarlet fever.