DermatologyTier 1Disease (DEADMAN)

Dermatitis - contact

Description

Inflammatory dermatitis from external exposure - two distinct mechanisms with different management
Irritant contact dermatitis (ICD, ~80%) - direct chemical/physical damage, dose-dependent, no prior sensitisation needed
Allergic contact dermatitis (ACD, ~20%) - type IV (delayed) hypersensitivity, requires prior sensitisation, occurs at any exposure dose once sensitised

One of the commonest occupational skin diseases - hairdressers, healthcare workers, cleaners, construction (cement)
ICD - more common overall; hands the commonest site (wet work, detergents)
ACD - increases with cumulative allergen exposure over a lifetime; nickel is the commonest allergen in the general population (F>M, ear piercing/jewellery)

Irritant

Direct cytotoxic damage to keratinocytes/barrier disruption - water, detergents, solvents, acids/alkalis, friction
Cumulative/chronic low-grade exposure (wet work) - commonest real-world pattern, not single high-dose injury

Allergic - type IV hypersensitivity

Sensitisation phase: hapten penetrates skin, binds carrier protein -> Langerhans cell presents to naive T cells -> memory T cells
Elicitation phase (on re-exposure, 24-72h later): memory T cells -> cytokine release -> eczematous reaction
Common allergens: nickel (jewellery, belt buckles), fragrance, preservatives (methylisothiazolinone), rubber accelerators, topical antibiotics (neomycin), hair dye (para-phenylenediamine), corticosteroids themselves

Clinical

ICD: glazed, dry, fissured erythema, confined tightly to the contact area, often hands; onset can be immediate or cumulative
ACD: eczematous, vesicular, weeping, may extend beyond the contact site; distribution often diagnostic (earlobes = nickel, eyelids/face = airborne or transferred allergen, feet dorsum = shoe allergens)
History of occupation, hobbies, cosmetics/products, timing relative to exposure is key

Patch testing - confirms ACD and identifies the allergen

Gold standard for ACD diagnosis - standardised allergen series applied to back, read at 48h and 72-96h
Not useful for ICD (irritant reactions can false-positive on patch testing - a separate read/interpretation skill)
Indicated when: dermatitis fails to respond to standard therapy, occupational relevance, distribution suggests a specific allergen

A. Both types - foundational

Identify and avoid the trigger - single most important step; without avoidance, topical therapy only controls, does not resolve
Emollients, soap substitutes, barrier creams/gloves for wet work

B. Acute flare

Topical corticosteroid - potency matched to site/severity, short course
Wet dressings/soaks for weeping acute ACD
Oral corticosteroid short course for severe/extensive ACD (e.g. plant-derived allergens with facial involvement)

C. Allergic - allergen-specific

Patch test result -> specific avoidance advice (product substitution lists, occupational modification)
Occupational cases - workplace risk assessment, may need role modification if avoidance not feasible

D. Chronic/refractory hand dermatitis

Topical calcineurin inhibitors as steroid-sparing option
Consider alitretinoin (severe chronic hand eczema unresponsive to potent topical steroids) or phototherapy

Atopic dermatitis - impaired barrier predisposes to both ICD and ACD ("atopic hand dermatitis" overlap)
Occupational exposure - hairdressing, healthcare, cleaning, metalwork, construction
Nickel allergy - strongly associated with ear/body piercing
Concurrent allergic contact dermatitis to a topical treatment (e.g. preservative in an emollient) can mimic treatment failure - consider the product itself as the allergen

With effective avoidance - most resolve or improve substantially over weeks
Chronic occupational exposure without avoidance - lichenification, chronic fissuring, secondary infection, significant work disability
Once sensitised (ACD), the allergy is generally lifelong - re-exposure at any point triggers recurrence
Chronic hand dermatitis - a leading cause of workers' compensation claims in high-exposure occupations

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