Chemical Leukoderma after Allergic Contact Dermatitis and Patch Testing

<u><b><i></i></b></u> Chemical leukoderma (CL) is an acquired depigmentation condition caused by repeated exposure to melanocytotoxic chemicals that can occur in the presence or absence of allergic contact dermatitis (ACD). Chemicals containing aromatic or aliphatic derivatives such as phenols and catechols have been shown to have melanocytotoxic properties that contribute to the pathogenesis of CL. Lesions are clinically and histologically indistinguishable from vitiligo and can occur in the absence of preexisting inflammatory cutaneous disease or vitiligo. CL often occurs after the use of personal care products or through occupational exposure (such as personal protective equipment). It is a growing phenomenon that has affected patients worldwide and can especially have detrimental psychosocial effects on patients with skin of color because of the sharp contrast between the leukoderma and the background pigmentation of the unaffected skin. A large number of reports of ACD preceding CL in the past five decades suggest that sensitization to allergens containing both aromatic and nonaromatic compounds may be contributory to the development of contact hypersensitivity reaction followed by leukoderma weeks to months after initial exposure. The most commonly reported allergen among these case reports is para-phenylenediamine, an agent used in hair dye and frequently as a darkening agent in henna tattoos. This review provides an overview of the pathophysiology and factors related to CL after ACD or diagnostic patch testing and the allergens related to this disorder of pigmentation.