Why might adult bruise very easily? Often have bruises on legs of unknown origin. Is ther treatment?

Are you . Taking any blood thinners or baby aspirin? This can be a cause. Start with pcp.
Many possible causes. Many conditions can cause easy bruising in adults. A doctor's evaluation will help figure out the problem. Possible causes include: low platelets due to auto-immune destruction of platelets or due to problems making new platelets, blood cancers such as leukemia, clotting problems due to medications like aspirin, fragile capillary blood vessels, etc... Treatments are usually available.