Bruising is caused by ruptures or tears of the small blood vessels located beneath the skin; typically, bruises arise after falls or bumps. When these small blood vessels tear, blood leaks into the tissue beneath the skin, and the result is the black or blue patch of discoloration on the skin known as a bruise, according to WebMD.
Bruises are initially black or blue, but they tend to change colors as they heal. Bruises often go from a purple-black color to bluish-red or greenish-yellow before they heal. The time frame for healing is generally two to four weeks after the bruise occurs. Bruises are generally not a cause for concern, but severe bruising accompanied by pain and swelling, may signify a more serious issue like a fracture or a sprain, and may necessitate further medical evaluation warns WebMD.
Some people bruise more easily than others, but this doesn't necessarily mean that there is an underlying health problem. Older people bruise more readily because their skin is thinner and not as flexible as that of younger people. Women tend to bruise more easily than men, especially on the upper arms, buttocks and thighs.
When blood collects and pools beneath the skin and develops under the skin to form a hematoma, it is still usually not a reason to worry. It will feel lumpy and spongy, but hematomas do not cause blood clots.