Allergic Contact Dermatitis

Allergic contact dermatitis (ACD) is caused by a delayed hypersensitivity reaction within the skin, manifesting as a pruritic dermatitis initially at the site of skin contact with the allergen. Clinical patterns will vary based on the actual allergen involved, but eyelid dermatitis is very suggestive of ACD. ACD may coexist with irritant contact dermatitis, contact urticaria, and various forms of endogenous eczema which can complicate establishing an accurate diagnosis. ACD is diagnosed via the combination of patch testing and history of a clinically relevant exposure. Patch testing consists of placing allergens, most often on the back, and producing a cutaneous reaction that usually appears days to a week later. There are a number of regional baseline series used for patch testing, which have been developed to incorporate the most important allergens in different geographical locations. These include metals (e.g. nickel, chromate), fragrances, preservatives (e.g. methylisothiazolinone), formaldehyde and formaldehyde releasers (e.g. quaternium-15), the hair dye p-phenylenediamine, topical antibiotics (e.g. neomycin, bacitracin), and rubber accelerators. The most important aspect of treatment is allergen avoidance. In addition, skin inflammation is addressed by topical corticosteroids, moisturizing creams, and avoidance of skin irritants.