Contact Dermatitis, Occupational and Environmental Dermatology
Scope
This domain tests allergic versus irritant contact dermatitis, patch testing, occupational exposures, and environmental skin disease.
Core rules
- Allergic contact dermatitis is type IV delayed hypersensitivity; irritant contact dermatitis is direct toxicity without sensitization.
- Common allergens: nickel, cobalt, chromate, fragrance mix, paraphenylenediamine (PPD), rubber accelerators, methylisothiazolinone, formaldehyde.
- Occupational patterns: cement workers (chromate), hairdressers (PPD, ammonium persulfate), healthcare workers (latex, glutaraldehyde), florists (sesquiterpene lactones).
- Patch testing: apply to back, read at 48 and 72–96 hours; use appropriate concentrations.
- Photodermatoses: polymorphic light eruption, photoallergy, phytophotodermatitis (furocoumarins).
- Environmental: heat (miliaria), cold (chilblains), radiation, air pollution.
Worked example
A hairdresser has chronic hand eczema. Reasoning: occupational exposure to PPD and shampoos suggests allergic contact dermatitis; patch testing with a standard series plus hairdressing series identifies the allergen, and avoidance plus gloves are essential.
Traps
Patch test readings must be delayed; an immediate reading misses delayed reactions. Nickel allergy is not synonymous with all metal allergy. Irritant dermatitis can mimic allergy, so patch testing is needed before labeling.