Photocontact dermatitis and chloracne: two major occupational and environmental skin diseases induced by different actions of halogenated chemicals.

Among occupational and environmental disorders, contact or photocontact dermatitis and an acneiform eruption are two major skin disorders. Photocontact dermatitis was historically caused by various halogenated salicylanilides, while the acne is induced by halogenated aromatic hydrocarbons and thus called chloracne. Therefore, it should be noted that halogenated chemical compounds are important causative agents in the occupational and environmental medicine. In photocontact dermatitis, photoconjugation of epidermal cells with a photohaptenic halogenated chemical is the initial step. Langerhans cells serve as antigen-presenting cells and T cells sensitized by photoantigen-bearing Langerhans cells induce this photosensitivity. On the other hand, in chloracne, halogeneted hydrocarbons render keratinocytes of the outer root sheath and sebaceous duct hyperplastic. The dilated infundibulum of most hair follicles is then filled with comedone that consist of many accumulated layers of keratinized cells and sebum. Therefore, halogenated chemicals exhibit different actions, i.e. the induction of an immunologic consequence and the modulation of keratinocyte biology. These two conditions also provide good experimental models for investigating dermatology.