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.
Melasma consists of dark brown, sharply marginated, roughly symmetric patches of hyperpigmentation on the face (usually on the forehead, temples, cheeks, upper lip, or nose). It occurs primarily in pregnant women (melasma gravidarum, or the mask of pregnancy) and in women taking oral contraceptives. Ten percent of cases occur in nonpregnant women and dark-skinned men. Melasma is more prevalent among and lasts longer in people with dark skin.
Because melasma risk increases with increasing sun exposure, the mechanism probably involves overproduction of melanin by hyperfunctional melanocytes. Other than sun exposure, aggravating factors include
• Autoimmune thyroid disorders
• Photosensitizing drugs
In women, melasma fades slowly and incompletely after childbirth or cessation of hormone use. In men, melasma rarely fades.
Lentigines (singular: lentigo) are flat, tan to brown, oval macules. They are commonly due to chronic sun exposure (solar lentigines; sometimes called liver spots) and occur most frequently on the face and back of the hands. They typically first appear during middle age and increase in number with age. Although progression from lentigines to melanoma has not been established, lentigines are an independent risk factor for melanoma. If lentigines are a cosmetic concern, they are treated with cryotherapy or laser; hydroquinone is not effective.
Nonsolar lentigines are sometimes associated with systemic disorders, such as Peutz-Jeghers syndrome (in which profuse lentigines of the lips occur), multiple lentigines syndrome (Leopard syndrome), or xeroderma pigmentosum.
Changes are usually diffuse but sometimes have drug-specific distribution patterns or hues. Mechanisms include
• Increased melanin in the epidermis (tends to be more brown)
• Melanin in the epidermis and high dermis (mostly brown with hints of gray or blue)
• Increased melanin in the dermis (tends to be more grayish or blue)
• Dermal deposition of the drug, metabolite, or drug–melanin complexes (usually slate or bluish gray)
Drugs may cause secondary hyperpigmentation. For example, focal hyperpigmentation frequently occurs after drug-induced lichen planus (also known as lichenoid drug eruption).