People typically get bruises when they bump into something or when something bumps into them. Risk factors for bruises include the following:
Bruises can occur in some people who exercise rigorously, such as athletes and weight lifters. These bruises result from microscopic tears in blood vessels under the skin. Bruising in athletes can also result from direct impact/trauma and be accompanied by an underlying hematoma.
Unexplained, random bruises that occur easily or for no apparent reason may indicate a bleeding disorder or result from blood-thinning medications (anticoagulants), especially if the bruising is accompanied by frequent nosebleeds or bleeding gums.
Often, what are thought to be unexplained bruises on the shin or the thigh, for example, actually result from bumps into a bedpost or other object and failing to recall the injury.
Bruises in elderly people frequently occur because their skin has become thinner with age. The tissues that support the underlying blood vessels have become more fragile.
Bruising occurs more commonly with vitamin C deficiency (ascorbic acid deficiency or scurvy).
Bruising can be a sign of physical abuse of the child (child abuse).