What causes blood bruises under the skin and how can they be prevented or treated effectively?

Blood bruises under the skin, also known as hematomas, are caused by trauma or injury that damages blood vessels, causing blood to leak into the surrounding tissue. To prevent hematomas, it is important to avoid activities that may cause injury, such as rough sports or accidents. To treat hematomas effectively, applying ice to the area can help reduce swelling and pain. Elevating the affected area and applying compression can also help. In severe cases, medical attention may be necessary to drain the accumulated blood.