Publisher Summary This chapter examines the adverse effects of dermatological drugs, topical agents, and cosmetics. Contact allergy from corticosteroids occurs particularly in patients with a long history of topical corticosteroid use for atopic dermatitis, dermatitis of the hands or feet, stasis dermatitis caused by venous insufficiency, and chronic otitis externa. Most allergic patients suffer from chronic eczema that does not respond adequately to treatment with corticosteroids or even worsens during therapy. Moreover, an oral or parenteral administration of corticosteroids in presensitized patients can, within several hours to 2–3 days, give rise to the exacerbation of previously existing allergic contact dermatitis or widespread drug reactions, sometimes with blisters, urticaria, and purpura. Cross-reactions between two corticosteroids often occur, and a number of other steroids should preferably be patch tested before prescribing other corticosteroids for allergic patients. Clinical and electromyography (EMG) features of muscle damage have been reported with etretinate. Nonspecific gastrointestinal adverse effects of isotretinoin include anorexia, nausea, vomiting, and weight loss.