Pathophysiology of Seborrheic Dermatitis
Seborrheic dermatitis is a chronic inflammatory skin condition primarily caused by an abnormal inflammatory response to Malassezia yeasts, combined with skin barrier dysfunction, altered sebum composition, and host immune factors. 1
Core Pathophysiological Mechanisms
Malassezia Yeast Involvement
- Malassezia species (lipophilic yeasts) are considered a primary trigger in seborrheic dermatitis 1, 2
- These yeasts naturally colonize sebum-rich areas of the skin but can overgrow under certain conditions 3
- The inflammatory reaction against Malassezia is fundamental to seborrheic dermatitis development 3
- Malassezia can trigger both non-immune and immune-mediated inflammatory responses 3
Skin Barrier Dysfunction
- Recent evidence shows significant skin barrier impairment in lesional skin of seborrheic dermatitis 4
- Characterized by:
- Altered ceramide subclass composition
- Impaired chain elongation
- Increased chain unsaturation
- These changes correlate directly with barrier function impairment 4
Sebaceous Gland Activity
- Occurs predominantly in sebum-rich areas (scalp, face, ears, chest, upper back) 1
- Abnormal sebum production or composition creates favorable conditions for Malassezia overgrowth 5
- Changes in sebaceous activity may precede Malassezia overgrowth rather than result from it 5
Immune System Dysregulation
- Enhanced cell-mediated immunity to Malassezia has been detected in 40% of patients with chronic seborrheic dermatitis 6
- Abnormal or inflammatory immune response to Malassezia contributes to disease manifestation 2
- Genetic factors affecting host immunity may predispose to seborrheic dermatitis 5
Microbial Dysbiosis
- Beyond Malassezia, broader skin microbiota changes are observed 4:
- Increased Staphylococcus abundance
- Decreased Cutibacterium abundance
- These changes may contribute to inflammation and barrier dysfunction 4
Predisposing Factors
Medical Conditions
- More pronounced in patients with:
- HIV infection
- Parkinson's disease
- Down syndrome 1
Genetic Factors
- Genetic studies have identified potential contributors:
- ZNF750 mutation
- Insights from Mpzl3 knockout mice with SD-like phenotypes 5
Environmental Factors
- External factors can exacerbate the condition:
- Climate changes
- Stress
- Irritants 1
Emerging Pathophysiological Model
Recent evidence suggests a shift from the traditional Malassezia-centric view to a more complex model where:
- Intrinsic host factors (altered sebum, defective epidermal barrier) create conditions favorable for Malassezia overgrowth 5
- Malassezia proliferation triggers inflammatory responses 3
- Skin barrier dysfunction perpetuates inflammation and symptoms 4
- Microbial dysbiosis further contributes to inflammation 4
This multifactorial pathophysiology explains why treatments targeting different aspects of the disease (antifungals, anti-inflammatories, barrier repair) can be effective in managing seborrheic dermatitis 7.