Allergic contact dermatitis is the classic delayed hypersensitivity reaction, developing in two phases – sensitization and elicitation. It can have profound effects on affected individuals and may result in sickness, absence from work and increased health expense. Its diagnosis requires consideration of many factors including the patient's history and a physical examination; knowledge of the skin's reaction to various chemicals is also desirable. Above all, it requires a high degree of suspicion on the part of the clinician and tenacity, skill and experience in the investigator. The diagnosis can only be confirmed by interpreting patch test results and the technique in itself has many pitfalls for the unwary. Any sensitization identified needs to be put into the context of a past or present dermatitis, and explanations for allergen avoidance or substitution need to be provided for the patient.

Keywords allergic contact dermatitis, contact allergy, contact hypersensitivity, cutaneous allergy, skin allergy, dermatitis, occupational dermatitis, sensitization, elicitation, allergen, patch test, photopatch test, cosmetic allergy, medicament allergy, rubber allergy, metal allergy, fragrance allergy, preservative allergy