Allergic Contact Dermatitis (ACD)

Etiology: Type IV delayed-type hypersensitivity reaction of the skin. Develops following exposure to chemicals to which the individual has been previously sensitized; prevalence varies with allergen. Common allergens: poison ivy/oak/sumac, nickel, neomycin, bacitracin, rubber/latex, fragrances, formaldehyde.

History: Detailed history of exposure to allergens, workplace or hobbies; history of pre-existing skin disease (e.g., atopic or stasis dermatitis); medications.

Physical: Erythematous, scaling, papulovesicular dermatitis at sites of contact with the allergen; chronic—scaling lichenified dermatitis.

Investigations: Skin patch testing (on back) to establish diagnosis (different from prick testing).

DDx (ACD, ICD): Atopic or nummular dermatitis, drug reaction, scabies.

Management

• Proper counseling on allergen avoidance, including cross-reactants.
• Acute cases: Oral antihistamines, potent topical steroids or systemic prednisone in severe cases.
• Patients with multiple allergies or sensitivities should be advised to test out new skin care products by applying them to the inner aspect of their arm, twice a day without occlusion, for 1 wk before applying elsewhere on the body.