Hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin.
Hyperpigmentation can be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris. People with darker skin tones are more prone to hyperpigmentation, especially with 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 colour 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 concentration of the cells is greater, hyperpigmentation occurs. Another form of hyperpigmentation is post inflammatory hyperpigmentation. These are dark and discoloured spots that appear on the skin following acne that has healed.
Hyperpigmentation is associated with a number of diseases or conditions, including 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
- Acne scarring from post-inflammatary hyperpigmentation
- 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
- Coeliac disease
- Cronkite-Canada syndrome
- 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.
There are a wide range of depigmenting treatments used for hyperpigmentation conditions, and responses to most are variable.
Most often treatment of hyperpigmentation caused by melanin overproduction (such as melasma, acne scarring, liver spots) includes the use of topical depigmenting agents, which vary in their efficacy and safety, as well as in prescription rules. Several are prescription only in the US, especially in high doses, such as hydroquinone, azelaic acid, and koijic acid. Some are available without prescription, such as niacinamide, or cysteamine hydrochloride. Hydroquinone was the most commonly prescribed hyperpigmentation treatment before the long-term safety concerns were raised, and the use of it became more regulated in several countries and discouraged in general by WHO. For the US only 2% is at present sold over-the-counter, and 4% needs prescription. In the EU hydroquinone was banned from cosmetic applications. Treatments that do not involve topical agents are also available, including fraction lasers and dermabrasion.