Dark pigmentation appears on the legs for a variety of reasons. Regardless of the underlying cause, though, it is the result of the accumulation of melanin in localized spots. This condition is known as hyperpigmentation, and the American Osteopathic College of Dermatology identifies it as common and usually harmless. However, changes to your skin should be evaluated by a dermatologist, as they are sometimes a sign of melanoma and other skin cancers.
Causes
Dark pigmentation on the legs often results from years of exposure to ultraviolet radiation from the sun. Exposure via sun lamps and tanning beds can contribute as well, notes the American Academy of Dermatology on its AgingSkinNet website. Such areas of excess pigmentation are known as age spots or liver spots, and medically as solar lentigines. Dark pigmentation on the legs may also follow injury or skin conditions that cause inflammation, such as cuts, burns or acne breakouts. Melasma is another possibility, though it generally affects the face; however, it can manifest on the abdomen and elsewhere. The adrenal disorder Addison's disease is another possible cause.
Symptoms
Age spots are typically oval-shaped and flush with the skin's surface. These brown, gray or black spots appear on skin often exposed to the sun, including on the legs, back of the hands, forearms, shoulders, neck and face. They sometimes accompany other indications of sun damage, such as leathery skin, thinned skin, dry skin or wrinkles, notes MayoClinic.com. Melasma has a similar appearance, but pigmentation is more interconnected, rather than in separate spots. Post-inflammatory hyperpigmentation is most readily identifiable by noting whether excess pigmentation appears where there was some injury or inflammatory skin problem, and it may be accompanied by scarring. Weakness, fatigue and low blood pressure are other common symptoms of Addison's disease.
Diagnosis
A dermatologist is best suited for diagnosing areas of dark pigmentation on your legs. Expect to provide your medical and family medical history, particularly any incidences of skin cancer. You'll be asked about your lifelong outdoor, tanning and sun protection habits. If, with this information and a visual examination, your dermatologist has cause for concern, a skin biopsy is often performed. A sample of discolored skin is shaved or cut off for laboratory examination, often on the spot with local anesthesia. Blood tests check for Addison's disease.
Treatment
Assuming no cancer is found and dark pigmentation is not deemed pre-cancerous, no treatment is necessary for dark pigmentation on the legs. Some people opt to get treatment anyway for cosmetic purposes. Topical applications made from a variety of ingredients, such as hydroquinone or alpha-hydroxy acids, are available over the counter and by prescription to fade darkened skin. Cosmetic procedures, including cryosurgery, chemical peels and laser surgery, destroy affected areas of skin to allow unblemished skin to grow back in its place. Skin cancer treatments include surgical excision, radiation therapy, chemotherapy and others. Hydrocortisone or prednisone and fludrocortisone are staples of Addison's disease treatment.
Prevention
Of the typical causes of dark pigmentation on the legs, age spots and sometimes post-inflammatory hyperpigmentation can be prevented. Sun protection is key to preventing age spots and limiting their growth once they appear. Wear pants outdoors or liberally apply sun block to your legs. If you get a wound on your legs, keep it clean and covered. Avoid scratching or picking at injuries, acne, or other skin conditions.
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