How should I evaluate and treat a 1‑month‑old infant with facial or diaper skin lesions that may represent impetigo versus seborrheic dermatitis?

Distinguishing Impetigo from Seborrheic Dermatitis in a 1-Month-Old Infant

In a 1-month-old infant with facial or diaper area lesions, prioritize ruling out impetigo first through careful examination for honey-colored crusts, vesicles, or pustules, as this requires prompt antimicrobial treatment, whereas seborrheic dermatitis is a benign, self-limited condition requiring only emollients. 1

Key Clinical Distinctions

Impetigo Characteristics

• Nonbullous impetigo presents as erythematous papules that rapidly evolve into vesicles and pustules, then rupture to form thick honey-colored crusts, typically on exposed areas like the face and extremities 1
• Bullous impetigo (caused exclusively by toxin-producing S. aureus) manifests as fragile, thin-roofed vesicopustules that rupture easily 1
• Regional lymphadenitis may be present, though systemic symptoms are usually absent 1
• Lesions show progression over 4-6 days from pustules to crusted erosions 1

Seborrheic Dermatitis Characteristics

• Presents with greasy, yellowish scales (cradle cap) on the scalp, face, and diaper area with minimal to no pruritus 2, 3
• Characterized by erythematous patches with adherent, oily scales rather than honey-colored crusts 4, 2
• Self-limited condition with no systemic involvement 2
• Does not show the rapid vesicular-to-pustular evolution seen in impetigo 3

Diagnostic Approach

Physical Examination Priorities

• Look for honey-colored crusts – this is pathognomonic for impetigo and distinguishes it from seborrheic dermatitis 1
• Assess for vesicles, pustules, or weeping erosions – these indicate bacterial infection rather than inflammatory dermatosis 1
• Check for regional lymphadenopathy – suggests impetigo over seborrheic dermatitis 1
• Evaluate lesion distribution – impetigo favors exposed areas and shows discrete lesions, while seborrheic dermatitis affects sebaceous-rich areas (scalp, face, diaper region) with confluent scaling 1, 2

When to Obtain Cultures

• Obtain cultures of vesicle fluid, pus, or erosions if impetigo is suspected, particularly to guide treatment and identify MRSA 1, 5
• Cultures are especially important in neonates given the risk of serious bacterial infection 1

Treatment Algorithm

If Impetigo is Diagnosed

For Localized Disease:

• Topical mupirocin 2% ointment applied three times daily for 5-7 days is first-line treatment 1, 5
• Retapamulin 1% ointment twice daily for 5 days is an alternative 5

For Extensive Disease (multiple sites, widespread involvement):

• Oral antibiotics are mandatory when lesions are extensive, involve multiple sites, or topical therapy is impractical 1, 5
• For methicillin-susceptible S. aureus (MSSA): cephalexin (weight-adjusted dosing for infants) 1, 5
• For suspected MRSA: clindamycin (weight-adjusted) or trimethoprim-sulfamethoxazole 1, 5
• Treatment duration: 5-10 days for oral antibiotics 5
• Re-evaluate after 48-72 hours if no improvement 5

Critical Caveat: Penicillin alone is inadequate as it lacks coverage against S. aureus 5

If Seborrheic Dermatitis is Diagnosed

• Bland emollients (petrolatum-based, fragrance-free) applied liberally 2-3 times daily after bathing 6
• Gentle cleansing with water alone or nonsoap cleanser 2-3 times weekly 6
• Low-potency topical corticosteroids (class I-II) may be used sparingly for acute flares, but with extreme caution in infants due to risk of systemic absorption and iatrogenic Cushing syndrome 6
• Condition is self-limited and typically resolves without aggressive intervention 2

Common Pitfalls to Avoid

• Do not dismiss crusted lesions as "just cradle cap" – honey-colored crusts indicate bacterial infection requiring antimicrobial therapy 1
• Avoid topical steroids for impetigo – this can worsen infection and delay appropriate treatment 1
• Do not use tetracyclines (doxycycline) in infants, as they are contraindicated under 8 years of age 1, 5
• Recognize that conditions can coexist – impetiginized eczema represents secondary bacterial infection superimposed on inflammatory dermatosis 1
• Monitor for treatment failure – if no improvement after 48-72 hours of appropriate therapy, obtain cultures and consider MRSA or alternative diagnosis 5

Special Considerations for Neonates

• Impetigo neonatorum occurs in 11.3% of newborns and is more frequent in hot, humid climates 7
• Neonates with extensive impetigo require close monitoring for systemic infection given their immature immune systems 6
• Keep lesions covered with clean, dry bandages and maintain strict hygiene to prevent spread 1, 5
• Infantile eczema at 1 month (distinct from seborrheic dermatitis) is associated with cord blood eosinophilia and predicts subsequent atopic dermatitis, but this does not apply to seborrheic dermatitis 8