KidsHealth explains that some people bruise more easily than others because of differences in the toughness of the skin tissue, the presence of certain diseases or conditions and the effects of some medications. Blood vessels also usually become fragile over time, which is why older people tend to bruise more easily.
MedicineNet says on WebMD that the type of injury necessary to cause a bruise varies with age. Children often do not get bruised easily whereas elderly people experience extensive bruising, or ecchymosis, from minor bumps and scrapes. Sometimes they even bruise without prior injury. Certain medications also contribute to the amount of bruising as they interfere with blood clotting, resulting in more bleeding into the skin or tissues. Common medications associated with bruising include nonsteroidal anti-inflammatory medications, such as ibuprofen, naproxen and aspirin.
Warfarin is a medication that prevents clotting in patients with blood clots in their heart or legs, and it causes severe bruising, especially when taken in high levels, notes MedicineNet. Cortisone medications also lead to bruising as they increase the fragility of small blood vessels in the skin. Genetic clotting problems, such as hemophilia, and acquired clotting problems, such as liver diseases, also cause people to develop extensive bruising or even fatal bleeding.