 human exposure to 2,3,7,8-tetrachlorodibenzo - p - dioxin ( tcdd ) and chlorinated analogs commonly results in pathological changes in the skin and its appendages characterized by thickening of the epidermis ( acanthosis ) , hyperkeratosis and squamous metaplasia of the epithelial lining of the sebaceous glands . 
 acneform lesions ( chloracne ) develop as hair follicles dilate and fill with keratin and sebaceous glands become cystic . in animal models 
 it has been found that the chloracneogenic potential of the halogenated aromatic compounds examined corresponds with the relative affinity of these same compounds for the cytosolic tcdd receptor . 
 this receptor controls the coordinate expression of a number of inducible enzyme activities and in certain cell targets can alter normal programs of proliferation and differentiation . in this report 
 we describe some of our ongoing studies on the mechanisms of action of tcdd in normal human epidermal cells and squamous cell carcinoma ( scc ) lines . 
 these systems permit detailed investigation of the molecular and biochemical events underlying pathologic changes in the skin and offer the potential of establishing a risk assessment model for halogenated aromatic compounds by using human target cells.imagesfigure 2 . 
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