Different Types of Dermatitis
Dermatitis encompasses several distinct clinical entities, with the major types being atopic dermatitis (endogenous/constitutional), contact dermatitis (allergic and irritant), seborrheic dermatitis, and less common variants including dyshidrotic, nummular, and asteatotic dermatitis.
Primary Classification Framework
The classification of dermatitis fundamentally divides into endogenous (constitutional) and exogenous (environmental) forms 1.
Atopic Dermatitis (Endogenous)
- Most common form, affecting up to 25% of children and 2-3% of adults 2
- Chronic, pruritic inflammatory disease with onset typically between 3-6 months of age
- 60% develop symptoms in first year of life, 90% by age 5 2
- Associated with elevated IgE, personal/family history of allergic rhinitis and asthma
- Clinical features: erythema, edema, xerosis, erosions/excoriations, oozing, crusting, lichenification (varies by age and chronicity) 2
- Pruritus is the hallmark symptom
- Complex pathogenesis involving genetic factors, dysfunctional skin barrier, and immune dysregulation 2
Contact Dermatitis (Exogenous)
Contact dermatitis accounts for 4-7% of dermatological consultations and has a point prevalence of hand involvement at 2%, with 20% lifetime risk 1.
Two major subtypes:
Irritant Contact Dermatitis
- More common than allergic contact dermatitis (accounts for 80% of contact dermatitis cases) 3, 4
- Caused by direct chemical damage to skin barrier
- Results from exposure to wet agents (water, frequent handwashing) and harsh emulsifiers/surfactants 1
Allergic Contact Dermatitis
- Accounts for 20% of contact dermatitis cases 3, 4
- Carries worse prognosis than irritant contact dermatitis unless allergen identified and avoided 1
- Prevalence of contact allergy in European general population: 10-27% 1
- Most common allergens: nickel (14.5%), fragrance (37%), cobalt (22%), hydroxyisohexyl cyclohexene carboxaldehyde (14%), p-phenylenediamine (1%) 1
- Can persist even after allergen avoidance, particularly with chromate, epoxy resin, and Compositae allergies 1
Seborrheic Dermatitis
- Affects scalp, back, face, and chest 5
- In infancy, often difficult to separate from atopic dermatitis (may overlap) 2
- Key distinguishing feature: affects groin and axillary regions (which atopic dermatitis typically spares) and tends not to be pruritic 2
Other Dermatitis Subtypes
Less common but clinically important variants 5, 3:
- Dyshidrotic eczema: Develops on palms and soles
- Asteatotic dermatitis: Predominantly occurs in elderly patients
- Nummular eczema: Characterized by cylindrical-shaped lesions
- Photoinduced contact dermatitis: Requires light exposure for reaction 3
- Systemic contact dermatitis: Systemic exposure to allergen 3
- Non-eczematous contact dermatitis: Including erythema multiforme-like, purpuric, lichenoid, and pigmented variants 6
Critical Diagnostic Distinction
The pattern and morphology of dermatitis, particularly on hands and face, is unreliable in predicting cause and distinguishing atopic/endogenous from contact (irritant or allergic) dermatitis 1. This is true even in children with atopic dermatitis 1.
Essential Clinical Pitfall
Because clinical features alone cannot reliably distinguish between types, patch testing should be performed in any patient with chronic or persistent dermatitis, or in atopic dermatitis that was previously well-controlled but becomes difficult to control with the same treatments 1. The point prevalence of dermatitis in the U.K. is approximately 20%, with atopic/endogenous dermatitis comprising the majority 1.
Immunologic Insights
Recent research identified causal relationships between specific immunocyte phenotypes and dermatitis subtypes: 22 phenotypes associated with atopic dermatitis, 8 with contact dermatitis, 5 with infective dermatitis, and 6 with seborrheic dermatitis, with potential bidirectional interactions 7.