More often than not, bruising comes from physical impact or injury. When small blood vessels or capillaries are damaged, the leaking blood pools under the skin to form a bruise.
As the body reabsorbs the blood, the bruise disappears.
Bruises start out blue or purple, as the blood loses oxygen, and they turn yellow or green from compounds called biliverdin and bilirubin that the body produces when it breaks down hemoglobin.
Older people bruise more easily, as aging skin becomes thinner and loses some of the protective fatty layer underneath that helps cushion blood vessels from injury.
Blood vessels also lose some elasticity over time, while skin damage from sun exposure can cause blood vessels to break easily as well.
Consider your medications
Some bruising can be traced to ordinary medications people take every day. Over-the-counter anti-inflammatories such as ibuprofen and naproxen affect the blood’s ability to congeal or coagulate.
Taking aspirin regularly — which some people do to lower the risk of heart attack or stroke — can lead to bruising as well.
Blood thinners prescribed to lower the chances of developing blood clots can cause black-and-blue marks, as can clopidogrel, a drug some seniors take to help prevent heart disease and strokes.
Antidepressants also can lower the blood-platelet count, leaving fewer cells for clotting purposes.
Size up your vitamins
Certain vitamin deficiencies, such as a lack of vitamin K, can be an explanation.
A deficiency of vitamin K, found in green leafy vegetables, could indicate a more serious issue such as inflammatory bowel disease or celiac disease.
Someone lacking in iron, needed to make the hemoglobin for blood to carry oxygen throughout the body, might bruise easily.
Symptoms of iron-deficiency anemia also include severe fatigue, dizziness or shortness of breath.
Taking dietary supplements like fish oil, garlic, ginkgo and vitamin E also block platelets in the blood from clotting and can lead to easy bruising.
Check with your doctor
More seriously, liver disease such as cirrhosis can trigger bruising. The liver produces factors needed for blood clotting.
“Any problems with the liver can mess with proteins necessary for clotting,” said Dr. Neha Vyas, a family medicine physician at Ohio’s Cleveland Clinic. Kidney disease, too, affects platelets and therefore clotting, she said.
Other ailments that can impair the blood’s clotting ability are chronic inflammatory diseases, such as lupus and cancers such as Hodgkin’s disease, leukemia or multiple myeloma.
“It is important to seek medical attention if significant bruising occurs, since in some cases it can reveal health issues,” said Dr. Aarthi Anand, a geriatrician and family medicine practitioner in Los Angeles.
Alcohol causes blood vessels to relax and expand, making them more prone to breaking, and heavy drinking will lead to bruising as well.
Unexplained bruises can be nothing to worry about — especially bruises on the arms and legs, since many people knock into things without remembering they’ve done it. But unexplained bruises on the abdomen, back or face are more likely to signal an underlying condition.
Another potential cause for concern is bruising that appears suddenly.
“If your symptoms arise out of the blue, as in, you never had issues before, and then suddenly you start bleeding easily, it’s important to seek medical attention,” said Dr. Tania Elliott, a clinical instructor of medicine at NYU Langone Health in New York.