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Hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin. ==Causes== Hyperpigmentation can be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris. People with darker Asian, Mediterranean, or African skin tones are also more prone to hyperpigmentation, especially if they have excess sun exposure. Many forms of hyperpigmentation are caused by an excess production of melanin. Hyperpigmentation can be diffuse or focal, affecting such areas as the face and the back of the hands. Melanin is produced by melanocytes at the lower layer of the epidermis. Melanin is a class of pigment responsible for producing color in the body in places such as the eyes, skin, and hair. As the body ages, melanocyte distribution becomes less diffuse and its regulation less controlled by the body. UV light stimulates melanocyte activity, and where concentrations of the cells are denser than surrounding areas, hyperpigmentation is effected. Can also be caused by using skin lightening lotions. Another form of hyperpigmentation is post inflammatory hyperpigmentation. These are dark and discolored spots that appear on the skin following acne that has healed.〔(Hyperpigmentation on Face (Acne Scars} ) ''Hyperpigmentation, Dark Spots, Acne Scars, Meladerm".〕 Hyperpigmentation is associated with a number of diseases or conditions, including but not limited to the following: *Addison's disease and other sources of adrenal insufficiency, in which hormones that stimulate melanin synthesis, such as melanocyte-stimulating hormone (MSH), are frequently elevated. *Cushing's disease or other excessive adrenocorticotropic hormone (ACTH) production, because MSH production is a byproduct of ACTH synthesis from proopiomelanocortin (POMC). *Acanthosis nigricans – hyperpigmentation of intertriginous areas associated with insulin resistance. *Melasma, also known as ''chloasma'' – patchy hyperpigmentation often found in pregnant women. *Linea nigra – a hyperpigmented line found on the abdomen during pregnancy. *Peutz-Jeghers syndrome – an autosomal dominant disorder characterized by hyperpigmented macules on the lips and oral mucosa and gastrointestinal polyps. *Exposure to certain chemicals such as salicylic acid, bleomycin, and cisplatin. *Smoker's melanosis *Celiac disease *Cronkite-Canada syndrome *Porphyria *Tinea fungal infections such as ringworm *Haemochromatosis - a common but debilitating genetic disorder characterized by the chronic accumulation of iron in the body. *Mercury poisoning - particularly cases of cutaneous exposure resulting from the topical application of mercurial ointments or skin-whitening creams. *Aromatase deficiency *Nelson's syndrome *Grave's disease *As a result of tinea cruris. Hyperpigmentation can sometimes be induced by dermatological laser procedures. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hyperpigmentation」の詳細全文を読む スポンサード リンク
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