Size and shape
Bruise shapes may correspond directly to the instrument of injury or be modified by additional factors. Bruises often become more prominent as time lapses, resulting in additional size and swelling, and may grow to a large size over the course of the hours after the injury that caused the bruise was inflicted. Condition and type of tissue: In soft tissues, a larger area is bruised than would be in firmer tissue due to ease of blood to invade tissue. Age: elderly skin and other tissues are often thinner and less elastic and thus more prone to bruising. Gender: More bruising occurs in females due to increased subcutaneous fat. Skin tone: Discoloration caused by bruises is more prominent in lighter complexions. Diseases: Coagulation, platelet and blood vessel diseases or deficiencies can increase bruising due to more bleeding. Location: More extensive vascularity causes more bleeding. Areas such as the arms, knees, shins and the facial area are especially common bruise sites. Forces: Greater striking forces cause greater bruising. Genes: Despite having completely normal coagulation factors, natural redheads have been shown to bruise more, although this may just be due to greater visibility on commonly associated lighter complexion. Severity
Bruises can be scored on a scale from 0–5 to categorize the severity and danger of the injury. The harm score is determined by the extent and severity of the injuries to the organs and tissues causing the bruising, in turn depending on multiple factors.
For example, a contracted muscle will bruise more severely, as will tissues crushed against underlying bone. Capillaries vary in strength, stiffness and toughness, which can also vary by age and medical conditions. Low levels of damaging forces produce small bruises and generally cause the individual to feel minor pain straight away. Repeated impacts worsen bruises, increasing the harm level. Normally, light bruises heal nearly completely within two weeks, although duration is affected by variation in severity and individual healing processes; generally, more severe or deeper bruises take somewhat longer. Severe bruising (harm score 2–3) may be dangerous or cause serious complications. Further bleeding and excess fluid may accumulate causing a hard, fluctuating lump or swelling hematoma. This has the potential to cause compartment syndrome in which the swelling cuts off blood flow to the tissues. The trauma that induced the bruise may also have caused other severe and potentially fatal harm to internal organs. For example, impacts to the head can cause traumatic brain injury: bleeding, bruising and massive swelling of the brain with the potential to cause concussion, coma and death. Treatment for brain bruising may involve emergency surgery to relieve the pressure on the brain. Damage that causes bruising can also cause bones to be broken, tendons or muscles to be strained, ligaments to be sprained, or other tissue to be damaged. The symptoms and signs of these injuries may initially appear to be those of simple bruising.