In dermatology, hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin. Hyperpigmentation may be caused by sun damage, inflammation from acne, or other skin injuries. It is also associated with a number of diseases or conditions, including:

• Addison's disease and other sources of adrenal insufficiency, in which hormones that stimulate melanin synthesis (e.g. MSH) are frequently elevated.
• acanthosis nigricans, or hyperpigmentation of intertriginous areas associated with insulin resistance.
• chloasma, or 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.
• Certain chemicals such as Salicylic Acid.

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