Allergic contact dermatitis (Poison ivy) Contact dermatitis is a T cell-mediated delayed hypersensitivity response to a variety of different antigens. Acute lesions are characterized by erythema, vesiculation, and oozing, whereas chronic areas of involvement may be dry and lichenified.

The diagnosis of allergic contact dermatitis (ACD) is a simple one when there is a clear history of exposure to an allergen or when the distribution of the lesions provides a strong clue. At other times, the identification of the causative agent can be very difficult.

Allergic contact dermatitis (Poison ivy) A number of different plants are capable of causing contact dermatitis. By far, the most common are members of the genus Toxicodendron: poison ivy, oak, and sumac. Figures 10-3 and 10-4 are illustrations of contact dermatitis from poison ivy, the most common single cause of contact dermatitis in childhood.

The linear array of vesicles and bullae in Figures 10-1 and 10-2 reflects the pattern in which the resin was transferred from leaf to skin. Figures 10-3 and 10-4 show severe facial involvement and a more diffuse reaction. Children who experience recurrent episodes of this phytodermatitis should be encouraged to learn to recognize the causative plants.

Allergic contact dermatitis (wet wipes) Wet wipes containing the preservative methylisothiazolinone are a cause of ACD. This form of ACD can be misdiagnosed as psoriasis, eczema, or impetigo. Discontinuation of wet wipes results in a complete resolution of this dermatitis.

Allergic contact dermatitis (disposable diapers) Allergic reactions to the chemical components of a disposable diaper, including dye, may present as pictured in Fig. 10-6. “Lucky Luke” or “cowboy holster” dermatitis has the pattern of a cowboy’s gunbelt, with triangular-shaped erythema beneath the side bands of the diaper on the lateral buttocks, flanks, and upper lateral thighs.

Allergic contact dermatitis (mango) Contact dermatitis to mango may present as a chronic rash on the lips and around the mouth. Mango is a member to the Sumac family, and its sap contains the oil Urushiol. It is important to inquire about recent mango consumption when diagnosing an eruption like the one pictured in Fig. 10-7.

Allergic contact dermatitis (neomycin) The child in Fig. 10-8 has an ACD resulting from the repeated application of a preparation containing neomycin. The development or worsening of an eczematous eruption after the use of a topical medication, either prescribed or over-the-counter, should alert the physician to the possibility of a contact dermatitis (dermatitis medicamentosa). In addition to neomycin, common offenders are the stabilizer ethylenediamine and the paraben preservatives.