Unexplained bruising usually comes down to one of a handful of causes: medications or supplements that thin your blood, nutritional deficiencies, age-related skin changes, or less commonly, an underlying medical condition affecting your blood’s ability to clot. Most cases have a straightforward explanation once you look at the full picture.
Medications and Supplements
This is the most common and most overlooked cause. Many widely used medications reduce your blood’s ability to clot, which means even minor bumps you don’t notice can leave visible bruises. The usual suspects include aspirin, ibuprofen (Advil, Motrin), and naproxen (Aleve). If you take any of these regularly, even at low doses, they can be enough to tip the balance.
Prescription blood thinners like warfarin, apixaban, and rivaroxaban are well-known culprits, as are anti-platelet drugs prescribed after heart procedures. But some less obvious medications also play a role. Certain antibiotics and antidepressants can interfere with clotting. Corticosteroids, whether taken as pills or applied as creams over long periods, thin the skin itself, making blood vessels closer to the surface more vulnerable to breaking.
Dietary supplements are easy to forget when you’re trying to figure out what changed. Fish oil (omega-3 fatty acids), ginkgo biloba, garlic supplements, ginger, ginseng, turmeric, evening primrose oil, grapeseed extract, and even high-dose vitamins C and E all have mild blood-thinning effects. Individually they may not cause problems, but stack two or three of these together, or combine them with aspirin, and the effect adds up quickly.
Nutritional Deficiencies
Your body needs specific nutrients to keep blood vessels strong and to form clots properly. When those nutrients run low, bruising is one of the earliest visible signs.
Vitamin C is essential for producing collagen, the protein that reinforces the walls of your blood vessels. When you’re deficient, those vessel walls become fragile and break easily, even without significant impact. You might also notice tiny red spots on your skin or small vertical lines under your nails, both caused by the same weakened capillaries. Severe vitamin C deficiency (scurvy) is rare in developed countries, but mild deficiency is more common than people assume, particularly in older adults and people with very limited diets.
Vitamin K plays a direct role in producing the proteins your blood needs to clot. People on very restrictive diets, those with digestive conditions that impair fat absorption, or those on long-term antibiotics (which can kill the gut bacteria that help produce vitamin K) are most at risk. A simple blood test can identify whether a deficiency is contributing to your bruising.
Age-Related Skin and Vessel Changes
If you’re over 50 and noticing flat, purple bruises on your forearms and the backs of your hands, you’re likely seeing something called senile purpura. The name sounds alarming, but it’s extremely common and not dangerous.
What happens is a slow, cumulative process. Over decades, the collagen and elastin in your skin break down naturally. Sun exposure accelerates this significantly. Ultraviolet light penetrates into the deeper layers of skin, triggering damage that degrades the structural proteins holding everything together. The result is thinner skin with less cushioning around the small blood vessels underneath. Those vessels also become more permeable with age, allowing red blood cells to leak into surrounding tissue more easily. The bruises that result often look dramatic but are typically painless and heal on their own.
Liver Disease
Your liver manufactures most of the proteins your blood needs to form clots. When the liver is damaged, whether from alcohol use, hepatitis, fatty liver disease, or other causes, its ability to produce those clotting factors drops. Easy bruising is one of the earlier symptoms of cirrhosis, sometimes appearing before more obvious signs like jaundice or abdominal swelling. If you’re bruising easily and also experiencing fatigue, nausea, or swelling in your legs, liver function is worth investigating.
Blood and Clotting Disorders
A normal platelet count ranges from 150,000 to 450,000 per microliter of blood. When that number drops below 150,000, a condition called thrombocytopenia, your blood loses some of its ability to seal off injured vessels. Causes range from viral infections and autoimmune conditions to bone marrow problems and certain medications.
Von Willebrand disease is the most common inherited bleeding disorder. It involves a protein that helps platelets stick together and attach to damaged blood vessel walls. When that protein is low or doesn’t work correctly, even normal daily activity can produce noticeable bruises. Many people with mild forms don’t get diagnosed until adulthood, often after a dental procedure or surgery reveals unusual bleeding.
Leukemia and other blood cancers can cause unexplained bruising because they crowd out the normal cells in bone marrow responsible for producing platelets. This type of bruising tends to appear alongside other symptoms: persistent fatigue, frequent infections, unexplained weight loss, or bone pain.
Vasculitis and Autoimmune Conditions
Vasculitis is inflammation of the blood vessels themselves. When vessel walls become swollen and thickened, blood can leak through them, producing red or purple spots on the skin that look like bruises but don’t follow the usual pattern of fading from purple to green to yellow. Vasculitis can be triggered by infections, certain medications, or autoimmune diseases like lupus and rheumatoid arthritis. The spots often appear on the lower legs and may be accompanied by joint pain, fatigue, or numbness.
Bruise Patterns Worth Paying Attention To
Not all bruises carry the same significance. A bruise on your shin after bumping a coffee table is straightforward. But certain patterns suggest something beyond normal wear and tear. Bruises that appear on your torso, back, or thighs without any known injury deserve closer attention, since these areas are rarely subjected to the kind of accidental contact that causes bruising in healthy people. Large bruises that seem disproportionate to any possible cause, or bruises that keep appearing in clusters, are also worth investigating.
If bruising comes with other bleeding symptoms, like nosebleeds that won’t stop, bleeding gums, blood in your urine or stool, or unusually heavy menstrual periods, those are signals that your clotting system may not be functioning properly. The combination of bruising with extreme fatigue, unexplained fevers, or unintentional weight loss raises the priority further.
How Bruising Is Evaluated
When bruising needs investigation, the process typically starts with blood work. A complete blood count checks whether your platelet levels are in the normal range. A prothrombin time test measures how many seconds it takes for your blood to form a clot, and the results are converted into a standardized ratio (INR) so they can be compared consistently across different labs. A high INR means your blood is clotting too slowly. A low INR means it’s clotting faster than normal.
These tests, combined with a review of your medications, supplements, diet, and family history, are usually enough to identify the cause. In cases where initial testing is inconclusive, more specific tests for conditions like von Willebrand disease or liver function may follow. For most people, the answer turns out to be something manageable: a medication they didn’t realize was contributing, a supplement interaction, or a nutritional gap that’s easy to correct.