The primary reasons for bruising easily include aging (thinner skin and more fragile blood vessels), certain medications (blood thinners, steroids), vitamin deficiencies (especially vitamin C and K), genetic tendencies, liver disease, bleeding disorders (like hemophilia or von Willebrand disease), and conditions such as vasculitis. Other factors can be intensive physical activities, autoimmune disorders, and sometimes underlying cancers such as leukemia. If bruising is frequent, unexplained, or accompanied by other symptoms, it warrants a medical evaluation for serious conditions.