Allergic contact dermatitis (ACD) can be difficult to definitively diagnose when there is no identified allergen . However, eyelids are a common area for ACD, and edema is a strong diagnostic clue. In this case, ACD is the favored diagnosis.

Allergic contact dermatitis is a T cell -mediated type IV (delayed hypersensitivity) reaction that occurs after the skin comes in contact with an allergen. As with other type IV hypersensitivity reactions, the skin must have had prior exposure to the offending substance in order to become sensitized. Subsequent exposure leads to a hypersensitivity reaction that develops over the course of 2–3 days.

ACD accounts for 20 % of new cases of contact dermatitides, with the remaining 80 % being cases of irritant contact dermatitis [1]. A large retrospective study estimated the prevalence of contact allergies in the general population to be 21.2 % [2]. The prevalence varies by geographic region, due to differences in exposure, cultural customs, and environmental differences. Workers in certain occupations, especially hairdressers, barbers, metal workers, and health care professionals, are at higher risk for developing contact allergies [3, 4]. Of over 3700 chemicals implicated as causative agents of contact allergy, among the most common are nickel , thimerosal (antiseptic and antifungal agent), fragrance mix, neomycin, and formaldehyde (used as a preservative in many cosmetics ) [1, 2, 4, 5]. The estimated prevalence of contact allergy to cosmetics is 6 % in the general population [5]. Nickel allergies are more prevalent in women, and have been associated with a history of atopic dermatitis in women [2]. Women with pierced ears tend to present with nickel allergies more often than women without pierced ears [2].

Allergic contact dermatitis presents as an eczematous rash that can be severely pruritic. The rash tends to have sharply demarcated borders and is localized to the area exposed to the offending allergen . Any geometric or linear distribution of lesions may reveal a plant allergy, as the shapes are consistent with the area of skin that would come in contact with the plant. It is possible for the rash to develop beyond the site of exposure if the allergen is transferred by hands or clothing. Eyelids are susceptible to this kind of transfer, possibly because the thinner skin of the eyelids is more susceptible to reaction [1]. Eyelid ACD typically presents with edema. More severe cases of ACD may be vesicular or bullous.