Start with a common possibility: senile (actinic) purpura
One frequent cause of dark purple bruising on the arms and hands in older adults is senile purpura. These bruises tend to be larger than typical ones, may appear suddenly, and often take longer to fade. They are usually harmless, but because they can resemble bruising from other conditions, they are worth mentioning to your doctor. Noting their size, location, and frequency can be helpful.
