Unexplained bruising can be caused by aspirin or blood thinners, infections that cause toxins to accumulate in blood, hemophilia, von Willebrand's disease, lupus and liver disease, according to WebMD. Certain types of cancer, including Hodgkin's disease, multiple myeloma and leukemia can also cause unexplained bruising explains WebMD.
Other causes of unexplained bruising include an inflammation of the blood vessels known as vasculitis, malnutrition and nutritional deficiencies of folic acid, vitamin K, vitamin B12 and vitamin C, according to Cigna. The treatment for abnormal bruising includes adjusting or changing any medication that may be responsible for the bruising and treating the medical condition that is responsible for the bruising.
As the skin on the arms and legs becomes less flexible and thinner as a result of the aging process, it makes it easier for excessive bruising to occur, according to MD Health. Diabetes can cause bruising as a result of a disruption to the circulatory system. Grave's disease is an autoimmune disease that causes damage to the thyroid gland, causing it to produce excessive amounts of hormones, according to MD Health. When the thyroid gland becomes over-stimulated, it raises the metabolic rate, causing capillaries to become damaged, sometimes resulting in bruised skin.