Older adults often bruise easily from minor injuries, especially injuries to the forearms, hands, legs, and feet. As a person ages, the skin becomes less flexible and thinner because there is less fat under the skin. The cushioning effect of the skin decreases as the fat under the skin decreases. These changes, along with skin damage from exposure to the sun, cause blood vessels to break easily. When blood vessels break, bruising occurs.
Women bruise more easily than men, especially from minor injuries on the thighs, buttocks, and upper arms.
A tendency to bruise easily sometimes runs in families.

See: http://www.webmd.com/a-to-z-guides/bruises-and-blood-spots-under-the-skin-topic-overview
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Go see a medical doctor to make sure you don't suffer from some rare ailment. Otherwise, you could BLEED to death and won't realize it until you're DEAD.
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The presence of bruises may be seen in patients with platelet or coagulation disorders. Unexplained bruising may be a warning sign of child abuse or serious medical problems, such as leukemia and meningoccocal infection. Unexplained bruising could indicate internal bleeding or certain types of cancer. A deficiency in Vitamin C can also make a person more susceptible to bruises from impacts. Also long term glucocorticoid therapy can cause easy bruising.
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