Hyperpigmentation is darkening of the skin, most often caused by an abnormally high amount of the skin pigment melanin.
When exposed to sunlight, specialized skin cells called melanocytes (see Overview of Skin Pigment) produce increased amounts of the pigment melanin, causing the skin to darken, or tan. In some fair-skinned people, certain melanocytes produce more melanin than others in response to sunlight. This uneven melanin production results in spots of pigmentation known as freckles. A tendency to freckle runs in families. Other factors besides sunlight can cause increased melanin in spots or patches (localized) or in widespread areas of skin. Rarely, other substances besides melanin cause darkening of the skin.
Localized hyperpigmentation
Localized hyperpigmentation can be caused by
Skin injuries
Skin inflammation
Reactions to sunlight
Abnormal skin growths
Hyperpigmentation can develop after injuries such as cuts and burns or inflammation caused by disorders such as acne and lupus.
Some people develop hyperpigmentation in areas of skin that have been exposed to sunlight. Some plants (including limes, celery, and parsley) contain compounds called furocoumarins that make some people's skin more sensitive to the effects of ultraviolet light. This reaction is called phytophotodermatitis (see Chemical photosensitivity).
Hyperpigmentation can also occur in melasma, freckles, lentigines, and café-au-lait spots (flat, brown spots), as well as in abnormal skin growths such as moles and melanoma.
People who have a disorder called acanthosis nigricans develop darkened and thickened skin in the underarms, on the nape of the neck, and in skinfolds. Acanthosis nigricans can be a symptom of diabetes.
Lentigines
Lentigines (commonly called age spots or liver spots [but are not related to liver problems]) are flat, tan to brown, oval spots on the skin. A single spot is called a lentigo. They are a type of localized hyperpigmentation.
There are two types of lentigines:
Solar
Nonsolar
Solar lentigines are caused by sun exposure and are the most common type of lentigo. They occur most frequently on areas that are exposed to the sun, such as the face and back of the hands. They typically first appear during middle age and increase in number as people age. Lentigines are noncancerous (benign), but people who have them may be at higher risk of melanoma.
Nonsolar lentigines are not caused by sun exposure. Nonsolar lentigines sometimes occur in people with certain rare hereditary disorders, such as Peutz-Jeghers syndrome (characterized by many lentigines on the lips and polyps in the stomach and intestine), xeroderma pigmentosum, and multiple lentigines syndrome (LEOPARD syndrome).
Widespread hyperpigmentation
Widespread hyperpigmentation can be caused by
Changes in hormones
Internal diseases
Drugs and heavy metals
Hormonal changes may increase melanin production and darken the skin in Addison disease, in pregnancy, or with hormonal contraceptive use. A liver disorder called primary biliary cholangitis (previously called primary biliary cirrhosis) may also cause increased melanin production.
Some cases of hyperpigmentation are caused not by melanin but by other pigmented substances that are not normally present in the skin. Diseases such as hemochromatosis or hemosiderosis, which are caused by too much iron in the body, can cause hyperpigmentation. Some drugs and metals that are applied to the skin, swallowed, or injected can cause hyperpigmentation.
Hyperpigmentation caused by drugs and heavy metals
Drugs and heavy metals that can cause hyperpigmentation include the following:
Antimalarial drugs
Phenothiazines
Some cancer chemotherapy drugs
Some tricyclic antidepressants
Some heavy metals (such as silver, gold, and mercury, which can be poisonous)
The areas of hyperpigmentation are usually widespread, but some drugs can specifically affect certain areas. For example, some people develop fixed drug reactions, in which certain drugs (for example, certain antibiotics, nonsteroidal anti-inflammatory drugs [NSAIDs], and barbiturates) cause red patches or blisters to form in the same place on the skin every time the drug is taken. These reactions eventually lead to hyperpigmentation of the affected skin.
Depending on the drug or metal and where it is concentrated in the skin, hyperpigmentation may be violet, bluish black, yellow-brown, or shades of blue, silver, and gray (see also Color Changes in the Skin). In addition to the skin, the teeth, nails, white of the eyes (sclera), and lining of the mouth (mucosa) may be discolored. With many of these drugs, the hyperpigmentation often fades after the drug is stopped, but it can take longer to fade in people who have darker skin. Sometimes the hyperpigmentation is permanent regardless of skin color.
Because many drugs that cause skin pigmentation also cause photosensitivity reactions, people should avoid the sun.
