Purpura simplex is extremely common. The cause is not known. Some doctors think it may be a feature of many disorders, but others think it is a normal variation.
Aspirin and drugs that prevent blood clots (for example, warfarin), low body weight, prior use of corticosteroid drugs, and sun exposure may increase the risk of purpura simplex.
Purpura simplex usually affects women. Bruises develop on the thighs, buttocks, and upper arms in people without known injuries. People may have family members who also bruise easily. Although doctors often do tests of the blood clotting system Testing Bruising or bleeding after an injury is normal (see also How Blood Clots). However, some people have disorders that cause them to bruise or bleed too easily. Sometimes people bleed without any... read more 
to look for clotting abnormalities, no abnormalities are found (see also Bruising and Bleeding Bruising and Bleeding Bruising or bleeding after an injury is normal (see also How Blood Clots). However, some people have disorders that cause them to bruise or bleed too easily. Sometimes people bleed without any... read more ).
This condition is not serious, and no treatment is needed. However, sometimes doctors recommend that people avoid taking aspirin and aspirin-containing medications.
Bleeding under the skin may also be more common among older people (a condition called senile purpura Essentials for Older Adults Bruising or bleeding after an injury is normal (see also How Blood Clots). However, some people have disorders that cause them to bruise or bleed too easily. Sometimes people bleed without any... read more ). Senile purpura commonly causes bruising on the hands and forearms.
