The two types of<unk>  are endogenous and exogenous. The endogenous variety is an autosomal-recessive disease, known as alkaptonuria, that is caused by a lack of homogentisate oxidase enzyme. Exogenous<unk>  is an avoidable dermatitis that can be caused by the topical application of compounds such as hydroquinone or phenols. It was first seen in 1912, when a patient who used phenol on a leg ulcer was found by Beddard and Plumtre to have this condition. Hydroquinone-induced exogenous<unk>  was found in 1975 by Findlay, who observed the condition in patients who used skin lightening creams containing the compound. The three clinical stages of exogenous<unk>  are: # Erythema and mild hyperpigmentation # Hyperpigmentation and "caviar-like" lesions # Papulonodular lesions
Ochronosis
Zinc toxicity
Fluoride toxicity
Chromium toxicity
Copper toxicity
Lead poisoning
Skeletal fluorosis
Iron poisoning