Capillaries are the smallest blood vessels in the body, delivering nutrients and oxygen to body organs and whisking away chemical waste products. Capillaries are very thin and fragile, moving blood along a single blood cell at a time. Broken capillaries under the surface of the skin can appear as bruises or spider veins. There are many potential causes of unsightly, and sometimes unhealthful, broken capillaries in the legs, including injury and circulatory disorders.
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Bruises are the dark patches appearing on skin when the impact of a blow or injury breaks the capillaries just below the skin surface. Bumping into furniture or other impacts can cause broken capillaries and bruising on the legs. Both the arms and legs are common locations for bruises, according to the MayoClinic.com. As you age, the capillaries in the skin grow weaker, the Mayo Clinic advises, so burst capillaries and their resulting bruises become more common. Skin also becomes thinner with age, and the discoloration of broken capillaries can be more apparent, especially in areas such as the shins which lack a protective fatty layer. This makes bruising from broken capillaries more visible.
Heredity and Hormones
Heredity and hormonal changes including adolescence, pregnancy, menopause, or hormonal treatment, are all primary causes of broken capillaries, according to Continuum Health Partners, Inc., a nonprofit hospital system in New York City. Using birth control pills or other estrogen treatment can also weaken blood vessel walls and lead to spider veins, which are broken capillaries in the legs, as well as varicose veins, which are larger veins in the legs which have become nonfunctional and distended with blood.
Chronic Venous Insufficiency
Obesity, inactivity, or aging can result in chronic venous insufficiency, a potentially dangerous health condition in which blood pools in the lower portion of the legs because the pumping action of the veins is not strong enough to return the blood to the heart and keep it in circulation. Capillaries under the skin of the legs burst from the excessive pressure of the pooled blood, creating discolored patches on the legs. Without appropriate treatment, these areas of broken capillaries can develop into ulcerated sores, advises the Penn State University Milton S. Hershey Medical Center College of Medicine. Maintaining a healthy weight and engaging in regular exercise are the keys to keeping the "second heart" of muscles and circulatory vessels in the legs strong and functional, according to Continuum Health Partners, avoiding and minimizing development of new broken capillaries and other signs of circulatory disorders in the legs.