What is seborrheic dermatitis, its causes, symptoms, and treatment options, particularly in adults with oily skin or a history of psoriasis, eczema, or rosacea?

Seborrheic Dermatitis: Clinical Description

Seborrheic dermatitis is a chronic inflammatory skin condition affecting sebaceous-rich areas (scalp, face, chest) that presents with greasy yellowish scaling, erythema, and itching, caused by an inflammatory response to Malassezia yeast. 1

Clinical Presentation

Characteristic Features:

• Greasy yellowish scaling with erythematous patches on sebaceous-rich skin areas 1
• Primary locations: scalp, central face, ears, chest, back, axilla, and groin 2, 3
• Associated pruritus (itching) with secondary inflammation from Malassezia yeast 1
• Poorly defined erythematous patches with scaling 4

Distribution Pattern:

• In adults: scalp involvement ranges from mild patches to diffuse scaling 3
• Facial involvement: central face, eyebrows, nasolabial folds 2
• In infants: yellowish scaly patches on scalp ("cradle cap") 3

Pathophysiology and Causative Factors

Primary Mechanism:

• Malassezia species metabolize sebum triglycerides into irritating free fatty acids that trigger localized inflammation 5, 6
• Occurs specifically in areas with high sebaceous gland density 1
• Involves decreased fungal diversity with increased Malassezia colonization 6

Contributing Factors:

• Sebaceous gland activity and sebum production 3, 7
• Immune dysfunction and inflammatory response 3, 7
• Skin barrier dysfunction 7

Associated Conditions and Risk Factors

High-Risk Populations:

• More pronounced in: HIV infection, Parkinson's disease, and Down syndrome 1, 5, 6
• Frequently coexists with rosacea (51% of cases) 1, 6
• Associated with dry eye conditions (25-40% of cases) 1, 5, 6

Systemic Nature:

• 95% of patients with seborrheic blepharitis have seborrheic dermatitis elsewhere on the body 1, 5, 6
• Often coexists with other dermatologic conditions including eczema and psoriasis 1

Differential Diagnosis Considerations

Must Distinguish From:

• Atopic dermatitis: chronic pruritus starting in childhood, multiple body areas involved, different scaling pattern 1
• Psoriasis: characteristic silvery scale, indurated plaques, different distribution 1
• Contact dermatitis: history of allergen exposure, different clinical pattern 1
• In infants: difficult to separate from seborrheic dermatitis initially 1

Key Distinguishing Features:

• Seborrheic dermatitis: greasy yellowish scaling, affects sebaceous areas, spares groin/axilla 1
• Atopic dermatitis: xerotic scaling, lichenification, typically spares sebaceous areas 1

Treatment Approach

First-Line Therapy:

• Topical antifungals targeting Malassezia: ketoconazole, ciclopirox, miconazole 6, 8, 3, 7
• Ketoconazole 2% cream applied twice daily for four weeks or until clinical clearing 8

Adjunctive Anti-Inflammatory Treatment:

• Low-potency topical corticosteroids for short-term use to control inflammation and itching 5, 6, 9, 3
• Topical calcineurin inhibitors (tacrolimus, pimecrolimus) for facial involvement 1, 3, 7

Maintenance Therapy:

• Ongoing antifungal therapy required due to chronic relapsing nature 5, 6, 7
• Coal tar preparations for scalp involvement 10, 2
• Keratolytic agents (salicylic acid) and humectants (propylene glycol) 3

Severe or Resistant Cases:

• Systemic antifungals (terbinafine, itraconazole) reserved for widespread or refractory disease 2, 3
• UVB phototherapy may be considered 3

Clinical Pitfalls

Common Mistakes to Avoid:

• Failing to recognize the systemic nature—check for involvement at multiple sebaceous sites 5, 6
• Overlooking associated conditions (rosacea, dry eye) that require concurrent management 1, 6
• Using high-potency corticosteroids or prolonged steroid therapy—stick to low-potency short-term use 5, 6, 3
• Discontinuing treatment after initial clearing—maintenance antifungal therapy prevents relapse 5, 6, 7
• In immunocompromised patients (HIV, Parkinson's), expect more severe presentation requiring aggressive treatment 1, 5, 6