Seborrhoeic Dermatitis

Chronic inflammatory skin condition affecting sebaceous gland-rich areas, associated with Malassezia yeast overgrowth and individual inflammatory response to its metabolites (not a true infection).

Bimodal presentation: infantile (self-limiting, "cradle cap") and adult (chronic relapsing-remitting, worse with stress/immunosuppression, notably HIV, Parkinson's disease association).

Erythematous patches with greasy yellowish scale, affecting scalp, eyebrows, nasolabial folds, ears, central chest: classic sebum-rich distribution.

Scalp: dandruff (mild) to thick adherent scale (severe).

Mild itching (distinguishes from more intensely pruritic eczema). Infantile "cradle cap": thick yellow greasy scale on scalp, typically resolves by 6-12 months without treatment.

Clinical, based on characteristic distribution and greasy scale appearance. Skin scraping/KOH: not routinely needed, can help exclude tinea if diagnostic uncertainty. Consider HIV testing if severe/extensive/atypical/treatment-resistant presentation in adults (recognized association with immunosuppression).

Differentials: psoriasis (thicker, silvery scale, extensor surfaces, sharper demarcation, can overlap as "sebopsoriasis"), atopic dermatitis (more intensely itchy, different distribution), tinea capitis/corporis, contact dermatitis, rosacea.

• Scalp: antifungal shampoo (ketoconazole 2%, selenium sulfide, or zinc pyrithione) 2-3x/week, left on several minutes before rinsing; topical corticosteroid solution/scalp application for significant inflammation/itch (short courses)
• Face/body: topical antifungal (ketoconazole 2% cream od-bd), mild topical corticosteroid (hydrocortisone 1%) for flares (short courses, face-appropriate potency only), topical calcineurin inhibitor (tacrolimus/pimecrolimus) for maintenance/steroid-sparing particularly on face
• Gentle cleansing, avoid harsh/oily products
• Chronic relapsing course: maintenance antifungal shampoo/wash 1-2x/week even when clear reduces recurrence
• Infantile cradle cap: gentle brushing after softening scale with emollient/baby oil, mild baby shampoo, usually self-limiting, treatment mainly cosmetic/parental reassurance

Referral: dermatology for diagnostic uncertainty, severe/extensive/treatment-resistant disease, or if prompting concern for underlying immunosuppression workup.