What is the difference between roseola rash and scarlet fever rash?

Distinguishing Roseola from Scarlet Fever Rash

Roseola presents with a maculopapular rash that appears AFTER fever resolution, while scarlet fever develops a sandpaper-textured rash that appears DURING active fever and spreads from the upper trunk throughout the body, sparing the palms and soles.

Timing Relative to Fever

Roseola (Exanthem Subitum)

• High fever (39-40°C) lasts 3-5 days and resolves abruptly, THEN the rash appears upon defervescence 1, 2
• This characteristic sequence—fever followed by rash—is the key diagnostic feature that distinguishes roseola from other exanthems 3, 2
• The rash appears as the child suddenly feels better after days of high fever 1

Scarlet Fever

• Rash develops DURING active fever, not after fever resolution 3
• Fever and rash occur simultaneously as part of the acute illness presentation 3

Rash Characteristics and Distribution

Roseola

• Macular (flat) or maculopapular rash that is pink to rose-colored 4
• Distribution: trunk and extremities, typically sparing palms, soles, face, and scalp 5
• Non-pruritic (does not itch) 3
• Blanching, discrete lesions 5

Scarlet Fever

• Develops on upper trunk first, then spreads throughout the body 3
• Characteristically SPARES the palms and soles 3
• Sandpaper-textured appearance (fine, rough texture to touch) 3
• Associated with circumoral pallor (pale area around the mouth) and strawberry tongue (not seen in roseola) 3
• May be pruritic 3

Age and Clinical Context

Roseola

• Primarily affects infants and young children aged 6 months to 3 years 1, 2
• Approximately 90% of children infected by age 1, nearly 100% by age 3 1
• Caused by human herpesvirus 6 (HHV-6B) or HHV-7 1, 2
• Febrile seizures are a frequent complication during the high fever phase 2

Scarlet Fever

• Caused by group A streptococcal pharyngitis 4
• Associated with sore throat, pharyngeal erythema, and tonsillar exudates 3
• Can occur at various ages but commonly affects school-age children 3

Critical Diagnostic Algorithm

Step 1: Assess Fever-Rash Timing

• If rash appears AFTER fever breaks → Consider roseola 3, 2
• If rash appears DURING active fever → Consider scarlet fever or other causes 3

Step 2: Examine Rash Morphology

• Macular/maculopapular, blanching, non-textured → Roseola 5
• Sandpaper texture, erythematous, confluent → Scarlet fever 3

Step 3: Check Distribution Pattern

• Trunk/extremities sparing palms/soles/face → Roseola 5
• Upper trunk spreading to body, sparing palms/soles → Scarlet fever 3

Step 4: Look for Associated Features

• Roseola: Recent high fever for 3-5 days, possible febrile seizures, otherwise well-appearing child after defervescence 1, 2
• Scarlet fever: Concurrent pharyngitis, strawberry tongue, circumoral pallor 3

Common Pitfalls to Avoid

• Do not diagnose roseola if the rash appears while fever is still present—this violates the cardinal feature of roseola 3, 2
• Do not assume all childhood maculopapular rashes are benign—consider serious bacterial causes like meningococcemia if the child appears toxic or has petechial progression 4
• Remember that roseola diagnosis is primarily clinical—laboratory confirmation is rarely needed in typical presentations 2
• Consider that scarlet fever requires antibiotic treatment to prevent complications (rheumatic fever, post-streptococcal glomerulonephritis), while roseola is self-limited and requires only supportive care 3, 2

Management Implications

Roseola

• Supportive care only—no antiviral therapy indicated in immunocompetent children 1
• Recovery is usually complete with no significant sequelae 2
• Reassure parents that the rash appearance signals improvement, not worsening 2

Scarlet Fever

• Requires antibiotic therapy (typically penicillin or amoxicillin) to eradicate streptococcal infection 3
• Treatment prevents serious complications and reduces transmission 3