There can be many causes for unexplained bruising, including liver disease, clotting disorders or some cancers, according to WebMD. Unexplained bruises may also be a side effect of certain medications or dietary supplements.
Occasional unexplained bruising is fairly normal, particularly in people who tend to bruise easily, reports Columbia Health. In these cases, the affected person simply did not notice the mild injury that caused the bruise. Women may be more susceptible to this than men.
Blood thinners are the one of the most common medications that cause unexplained bruising, reports Columbia Health. Even mild blood thinners, such as aspirin, cause it. Corticosteroids also make it more likely, as can significant amounts of ginkgo, ginger, garlic or fish oil in the diet. Dietary deficiencies, such as a lack of vitamin B-12, vitamin C or folic acid, also cause bruising.
Leukemia is commonly associated with unexplained bruising, according to WebMD. Hodgkin's disease and multiple myeloma can also be responsible. Diseases that cause chronic inflammation, including lupus, also make unexplained bruising more likely. Sepsis, which is the buildup of infectious toxins in the blood, may also be responsible.
Frequent unexplained bruising or large, painful bruises that suddenly appear for no reason should be checked out by a doctor, suggests Columbia Health. Severe bruising after only mild injury and bruises that do not begin to heal within two weeks are also causes for concern.