Hyperpigmentation is the increase in the natural color of the skin.
Melanin, a brown pigment manufactured by certain cells in the skin called melanocytes, is responsible for skin color. Melanin production is stimulated by a pituitary hormone called melanocyte stimulating hormone (MSH). Other pigments appear in the skin much less often.
Causes and symptoms
Darkened spots on the skin come in several varieties. The most ominous is malignant melanoma, a very aggressive cancer that begins as an innocent mole. The majority of moles (nevus), however, are and remain benign (harmless). The average person has several dozen, and certain people with a hereditary excess may have hundreds. Freckles, age spots, and cafe au lait spots, known as ephelides, are always flat and not as dark. Cafe au lait spots are seen mostly in people with another hereditary disorder called neurofibromatosis. "Port wine stains" are congenital dark red blotches on the skin. Other common dark colorations on the skin are called keratosis and consist of locally overgrown layers of skin that are dark primarily because there is more tissue than normal. A few of these turn into skin cancers of a much less dangerous kind than melanoma.
Darkened regions of the skin occur as a result of abnormal tanning when the skin is sensitive to sunlight. Several diseases and many drugs can cause photosensitivity. Among the common drugs responsible for this uncommon reaction are birth control pills, antibiotics (sulfonamides and tetracyclines), diuretics, nonsteroidal anti-inflammatory drugs (NSAID), pain relievers, and some psychoactive medications. Some of the same drugs may also cause patches of discolored skin known as localized drug reactions and representing an allergy to that drug. Sunlight darkens an abnormal chemical in the skin of patients with porphyria cutanea tarda. Several endocrine diseases, some cancers, and several drugs abnormally stimulate melanocytes, usually through an overproduction of MSH. Arsenic poisoning and Addison's disease are among these causes. A condition known as acanthosis nigricans is a velvety darkening of skin in folded areas (arm pits, groin, and neck) that can signal a cancer or hormone imbalance.
Of particular note is a condition called melasma (dark pigmentation of the skin), caused by the female hormone estrogen. Normal in pregnancy, this brownish discoloration of the face can also happen with birth control pills that contain estrogen.
Overall darkening of the skin may be due to pigmented chemicals in the skin. Silver, gold, and iron each have a characteristic color when visible in the skin. Several drugs and body chemicals, like bilirubin, can end up as deposits in the skin and discolor it.
The pattern of discoloration is immediately visible to the trained dermatologist, a physician specializing in skin diseases, and may be all that is required to name and characterize the discoloration. Many of these pigment changes are signs of internal disease that must be identified. Pigmentation changes may also be caused by medication, and the drug responsible for the reaction must be identified and removed.
Skin sensitive to sunlight must be protected by shade or sunscreens with an SPF of 15 or greater. Skin cancers must be, and unsightly benign lesions may be, surgically removed. Laser surgery is an effective removal technique for many localized lesions. Because it spreads so rapidly, melanoma should be immediately removed, as well as some of the surrounding tissue to prevent regrowth.
Sunlight is the leading cause of dark spots on the skin, so shade and sunscreens are necessary preventive strategies, especially in people who burn easily.
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J. Ricker Polsdorfer, MD
Addison's disease—A degenerative disease that is characterized by weight loss, low blood pressure, extreme weakness, and dark brown pigmentation of the skin.
Dermatologist—A physician specializing in the study of skin conditions and diseases
Diuretic—A cause of increased urine flow.
Keratosis—A skin disease characterized by an over-growth of skin, which usually appears discolored.
Lesion—Any localized abnormality.
Melasma—Dark pigmentation of the skin.
Nevus—Birthmark or mole.
Porphyria cutanea tarda—An inherited disease that results in the overproduction of porphyrins.
Syndrome—Common features of a disease or features that appear together often enough to suggest they may represent a single, as yet unknown, disease entity.