Bruises typically form when the impact of a blow or injury causes small blood vessels (capillaries) near the skin surface (epidermis) to rupture. The blood then leaks out of the vessel and appears as a reddish-purple mark. Eventually, the body reabsorbs the blood and the mark slowly fades.

Bruising of the hands and arms associated with actinic purpura is usually due to the aging process. The skin becomes thinner as a person ages and loses some of the layers that cushion blood vessels against injury (dermis). In addition, aging causes the tissues that support capillaries to weaken, leaving capillary walls more vulnerable to rupture. Although the incidence of actinic purpura increases with age, it can occur in younger patients.

Excessive exposure to the sun is also a major contributor to actinic purpura. Years of sun exposure damages the skin and weakens the blood vessel walls.

Bruising of the hands and arms can be made worse by use of anticoagulants (medications that stop blood from clotting, including aspirin), alcohol (which thins the blood) and corticosteroids (which may thin the skin). Dietary supplements, such as fish oil, ginkgo, ginger and garlic, also may have a blood-thinning effect that leads to increased bruising.