Dark spots or patches on the skin are not uncommon, but there are numerous potential causes for this irregularity. Some of these causes tend to disproportionately affect the skin on the lower calves, while others may appear anywhere on the body. Some may also be related to external treatment of the skin, while others involve conditions that cause dark skin from the inside out.
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Petechiae is a condition in which small blood vessels bleed beneath the surface of the skin, giving the impression of dark splotches or specks. They appear most frequently in parts of the body where blood pressure is the highest, such as the feet, ankles and lower calves, according to the MayoClinic.com. They may, however, appear anywhere. Petechiae marks can indicate low blood platelet counts and other conditions that affect normal blood clotting, or they may be caused by some medications.
According to the American Osteopathic College of Dermatology, hyperpigmentation is a condition that causes excess production of melanin, the body's natural pigment. There are several different types of hyperpigmentation, as well as several causes, and affected skin may be anywhere on the body. One of the most common forms is known as age or liver spots, which can appear during old age or after repeated sun damage. Hormone fluctuations may also cause hyperpigmentation; women who are pregnant or on birth control may experience its effects.
Acanthosis nigricans, a condition caused by elevated blood insulin levels, is also characterized by patches of skin that are noticeably dark and rough, according to the MayoClinic.com. The most commonly affected skin is on the neck, armpits and groin, but it may affect lower calf skin and other areas of the body. It is associated with obesity and diabetes, and is most effectively controlled through weight loss, medication and other efforts aimed at lowering insulin levels.
Poor Skin Care
Negligent skin care may also result in darkened pigmentation, according to "The New Science of Perfect Skin: Understanding Skin Care Myths and Miracles For Radiant Skin at Any Age" by Daniel Yarosh. The skin has a natural exfoliation process through which it attempts to shed dead skin cells, but it cannot always sufficiently keep up without intervention. When dead skin cells build up, they can darken skin tone. Excessively dry skin may also have this appearance. Regular washing, exfoliating and moisturizing can treat and prevent darkened skin related to this cause.
If you wear tight pants, tall boots or any other foot or leg wear that frequently abrades your lower calves, the darkened skin may be caused by friction, according to Yarosh. Routine friction makes skin dry and irritated, and over time, this can make the skin appear darker even when friction hasn't occurred recently.