Seborrheic Dermatitis
Dermatology
Illness script · Dermatology
Seborrheic Dermatitis
Chronic, relapsing inflammatory skin condition causing greasy, yellowish scales and erythema in sebaceous gland-rich areas.
This illness script for Seborrheic Dermatitis covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Bimodal: infants (cradle cap) and adults aged 30–60
- Male predominance
- Strongly associated with Parkinson's disease and other neurological conditions
- Immunocompromised states — especially HIV/AIDS (severe, refractory disease)
- Malassezia yeast overgrowth triggered by stress, cold weather, fatigue
- Medications: lithium, haloperidol, interferon can exacerbate
02
Presentation
- Greasy, yellowish-white scales on erythematous base — classic appearance
- Distribution: scalp (dandruff), nasolabial folds, eyebrows, retroauricular, central chest
- Pruritus is common but usually mild
- Infants: thick, adherent "cradle cap" on vertex scalp — non-inflammatory, non-pruritic
- Chronic course with flares; worsens in winter and with stress
- Blepharitis (eyelid margin scaling) may accompany facial involvement
03
Pathophysiology
- Malassezia (Pityrosporum) yeast overgrowth in sebum-rich areas triggers inflammatory cascade
- Abnormal host immune response to Malassezia metabolites (oleic acid) disrupts skin barrier
- Sebaceous gland hyperactivity provides substrate for yeast proliferation
- Result: epidermal hyperproliferation, spongiosis, and visible scaling
04
Diagnostics
- Primarily a clinical diagnosis — no labs required
- KOH prep not needed but can show Malassezia if performed
- Skin biopsy (if atypical): spongiosis + parakeratosis + perifollicular neutrophils
- Severe/refractory cases → check HIV status
- Patch test if allergic contact dermatitis is in the differential
05
Management
- Scalp: selenium sulfide, zinc pyrithione, or ketoconazole 2% shampoo — first-line
- Facial/body: topical low-potency corticosteroids (hydrocortisone) for acute flares
- Topical antifungals (ketoconazole cream) for maintenance to reduce Malassezia
- Calcineurin inhibitors (tacrolimus, pimecrolimus) — steroid-sparing for face/skin folds
- Avoid high-potency steroids on face long-term (atrophy, rosacea, telangiectasias)
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Psoriasis
Psoriasis has thick, silvery-white (not greasy yellow) plaques with well-demarcated borders and Auspitz sign; involves extensor surfaces.
Tinea capitis
Tinea capitis causes patchy alopecia with broken hairs and is confirmed by KOH prep; predominantly in prepubertal children.
Atopic dermatitis
Atopic dermatitis is intensely pruritic, affects flexural creases (antecubital, popliteal), and is associated with atopy/asthma/allergic rhinitis.
Rosacea
Rosacea features centrofacial erythema, telangiectasias, and papulopustules without greasy scaling or scalp/ear involvement.
Keep reading
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.