What causes seborrheic dermatitis?

Causes of Seborrheic Dermatitis

Seborrheic dermatitis is primarily caused by an inflammatory reaction to Malassezia yeasts (particularly Malassezia ovale/furfur) in combination with genetic predisposition, sebaceous gland activity, and immune system factors. 1, 2

Primary Causative Factors

1. Malassezia Yeasts

• Malassezia species (formerly known as Pityrosporum) are lipophilic yeasts that naturally colonize sebum-rich areas of the skin
• These yeasts metabolize sebum, producing irritating byproducts that trigger inflammatory responses 1, 2
• The FDA-approved ketoconazole cream label specifically notes that the therapeutic effect in seborrheic dermatitis is likely due to the reduction of M. ovale 3

2. Sebaceous Gland Activity

• Occurs predominantly in sebum-rich areas of the body:
  • Scalp
  • Face (especially nasolabial folds, eyebrows, glabella)
  • Ears and retroauricular areas
  • Chest
  • Upper back
  • Skin folds (axillary, inframammary, inguinal) 1
• Increased sebum production provides an ideal environment for Malassezia proliferation 4

3. Immune Response

• Abnormal or inflammatory immune response to Malassezia yeasts 4
• Both non-immune and immune mechanisms (nonspecific and specific) are involved in pathogenesis 2
• The relative contribution of these mechanisms depends on:
  • Yeast quantity and virulence
  • Individual immune reactivity 2

Contributing and Exacerbating Factors

1. Medical Conditions

• More pronounced in patients with:
  • HIV infection
  • Parkinson's disease
  • Down syndrome 1
  • Neurological disorders
  • Immunosuppression

2. Environmental Factors

• Winter temperatures can worsen symptoms 5
• Stress may trigger or exacerbate flares 5

3. Genetic Factors

• Genetic predisposition plays a role in susceptibility 1, 5
• Family history may be relevant

4. Hormonal Influences

• Androgens affect sebum production and composition 5
• Explains why seborrheic dermatitis often begins after puberty and can fluctuate with hormonal changes

Clinical Implications

The multifactorial nature of seborrheic dermatitis explains why treatment typically targets:

1. Antifungal therapy: To reduce Malassezia populations (ketoconazole, selenium sulfide, pyrithione zinc) 1, 3, 6
2. Anti-inflammatory agents: To control the inflammatory response (low-potency corticosteroids, calcineurin inhibitors) 1, 7
3. Maintenance therapy: Regular use of antifungal products and gentle cleansing to prevent recurrence 1

Common Pitfalls and Caveats

• Seborrheic dermatitis can be confused with other conditions like atopic dermatitis, psoriasis, or contact dermatitis 1
• In cases of severe or treatment-resistant seborrheic dermatitis, consider evaluating for underlying conditions like HIV or Parkinson's disease 1
• Prolonged use of potent topical corticosteroids should be avoided as they can potentially worsen skin conditions over time 1
• The condition is chronic and relapsing, so patient education about maintenance therapy is crucial 1, 7

Understanding the multifactorial etiology of seborrheic dermatitis helps guide appropriate treatment strategies and patient education about this common chronic inflammatory skin disorder.