The most common cause of skin bruising is bumping the body into something or something bumping into the body, according to WebMD. Some bruises do not have an explanation, but are often due to bumps that the person does not notice, or they may occur due to a blood disorder.
Bruises are more common in people who are taking blood-thinning medication, and bruising occurs more easily in older adults, explains WebMD. A bruise usually starts as a reddish color and turns blue or black within a couple of hours. After several days, it may turn green or yellow as it heals. A bruise is usually tender or painful for a few days, but as the color fades, so does the pain.
Most bruises heal on their own, and medical treatment is not necessary, claims WebMD. However, there are times when it is important to contact a doctor, including if the bruise appears with extreme pain or swelling, or if frequent bruising occurs without cause. It is also important to contact a doctor if the bruise does not improve within two weeks or does not go away in four weeks. If the person has a bruise on the head or eye, though it may cause anxiety, there is usually nothing serious happening, but if there is a blackout or signs of concussion, it is important to seek out emergency assistance.