Unexplained bruises—especially on arms, legs, or torso—can be more than just “aging.” While occasional bruising is normal, sudden or frequent bruises, especially with other symptoms, may signal serious health issues. Major causes include blood disorders like low platelets or leukemia (large bruises, petechiae, nosebleeds, fatigue), medication side effects (blood thinners, steroids causing easy bruising), vitamin deficiencies (C or K, slow-healing bruises, bleeding gums), autoimmune attacks (lupus, vasculitis causing bruises along vessels, joint pain, rashes), and liver disease (abdominal bruises, jaundice, swelling).