Hyperpigmentation

In dermatology, hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin.

Causes
Hyperpigmentation may be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris. People with darker Asian, east Indian, mediterranean or African skin tones are also more prone to hyperpigmentation especially if they have excess sun exposure.

Hyperpigmentation is 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.
 * Cushing's disease, excessive ACTH production; Melanocyte-Stimulating Hormone (MSH) production is a byproduct of ACTH synthesis from Proopiomelanocortin (POMC).
 * 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, bleomycin, and cisplatin.
 * Smoker's melanosis.
 * Celiac Disease.
 * Cronkite-Canada syndrome
 * Tinea fungal infections such as ringworm.

Hyperpigmentation can also be induced by dermatological laser procedures, although not common.

Treatment
Treatment of hyperpigmentation may include hydroquinone, kojic acid, azelaic acid, ascorbic acid, tretinoin (Retinol), topical glucocorticoids, and licorice extract. Note that all treatments will fail if the affected area is exposed to the sun and if there is not adequate UVA/UVB protection.