A bruise is a common skin injury formed when microvessels near the surface of the skin rupture and bleed. It is usually caused by bumps, taking medications, and certain illnesses. As we get older, the skin and blood vessels become thinner and more brittle, and minor bumps and contact may cause bruising to occur. Recent use of medications such as ibuprofen, aspirin, warfarin, antidepressants, antibiotics, chemotherapy, or a chronic deficiency of vitamin C or vitamin K can lead to a decrease in clotting factors in the blood, which can make bruising more likely to occur and more difficult to fade due to minor bumps. After distinguishing between the above two situations, if there are still some bruises with no obvious cause and accompanied by weight loss, fatigue, fever and other symptoms, it may be due to underlying diseases, such as liver, kidney, blood, certain genetic diseases, etc., and need to go to the hospital in time for checkups and treatments.