Unexplained bruising usually comes down to something your body is doing (or not doing) to protect your blood vessels. A bruise forms when tiny blood vessels under the skin break and leak blood into surrounding tissue, but your body can’t seal the damage quickly enough. In most cases, the cause is straightforward: a medication you’re taking, aging skin, or minor bumps you don’t remember. Less commonly, it signals a nutritional gap or an underlying health condition worth investigating.
How Bruises Actually Form
When a blood vessel wall gets disrupted, your body launches a repair process. Proteins beneath the vessel lining interact with platelets and clotting factors to plug the hole. If any step in that chain fails, blood leaks out and pools under the skin, creating the familiar discoloration that shifts from reddish-purple to brown over about 10 days.
Three things need to work properly to prevent excessive bruising: the blood vessels themselves need structural integrity, you need enough functioning platelets, and your clotting system needs to complete its cascade of chemical reactions. A problem at any one of these steps increases your risk of bruising, even from trivial contact.
Medications Are the Most Common Culprit
If you started bruising more easily after beginning a new medication, that’s likely your answer. Several common drug classes reduce your blood’s ability to clot. Over-the-counter pain relievers like aspirin, ibuprofen, and naproxen all interfere with platelet function. Prescription blood thinners like warfarin, apixaban, and rivaroxaban do it more aggressively. Anti-platelet medications prescribed after heart procedures have the same effect.
Some less obvious medications also contribute. Certain antibiotics and antidepressants can impair clotting. Corticosteroids, often prescribed for inflammation or autoimmune conditions, thin the skin itself, making blood vessels more vulnerable to breaking. If you’re on any of these, increased bruising is a known side effect rather than a mystery.
Supplements That Thin Your Blood
Dietary supplements are an overlooked cause. Fish oil (omega-3 fatty acids), ginkgo biloba, garlic, ginger, ginseng, turmeric, evening primrose oil, and high-dose vitamins C and E all have blood-thinning or anti-platelet properties. Individually, the effect may be mild. But if you’re stacking several of these, or combining them with aspirin or a prescription blood thinner, the cumulative impact on clotting can be significant enough to cause bruises from everyday contact you wouldn’t normally notice.
Aging Skin and Sun Damage
If you’re over 60 and noticing flat, purple bruises on your forearms and hands, you’re likely seeing a condition sometimes called senile purpura. It happens because years of sun exposure and natural aging break down the connective tissue that supports blood vessels in the skin. The skin and the tissue beneath it become thinner and more fragile, so even light pressure can rupture small vessels.
These bruises tend to appear on sun-exposed areas, particularly the backs of the hands and forearms. They’re cosmetically annoying but not dangerous on their own. They don’t indicate a clotting disorder. The underlying cause is structural: your blood vessels simply have less cushioning around them than they used to.
Nutritional Deficiencies
Vitamin and mineral deficiencies can cause bruising, though this is relatively rare in people eating a varied diet. The most well-known example is scurvy, caused by vitamin C deficiency. Vitamin C is essential for building collagen, the protein that gives blood vessel walls their strength. Without enough of it, vessels become fragile and leak easily.
Zinc deficiency and certain B vitamin deficiencies can also show up as unexplained bruising. Vitamin K, which your body needs to produce clotting factors, is another possibility, though true deficiency is uncommon in adults. If your diet is very restricted, you’ve had bariatric surgery, or you have a condition that impairs nutrient absorption, these deficiencies become more plausible.
Liver Disease
Your liver manufactures most of the proteins your blood needs to clot. When the liver is damaged, whether from chronic alcohol use, hepatitis, fatty liver disease, or cirrhosis, it produces fewer clotting factors. Liver disease also causes the spleen to enlarge, which traps and destroys platelets, further reducing your clotting ability. The combination of fewer clotting factors and fewer platelets means blood doesn’t seal vessel breaks efficiently, leading to easy bruising.
Bruising from liver disease rarely appears in isolation. You’d typically also notice fatigue, yellowing of the skin or eyes, swelling in the abdomen or legs, or spider-like blood vessels on the skin.
Bleeding Disorders
Some people bruise easily because they inherited a problem with their clotting system. Von Willebrand disease is the most common inherited bleeding disorder, affecting roughly 1 in 100 people to some degree. It causes a deficiency in a protein that helps platelets stick together. Many people with mild forms don’t know they have it until they notice they bruise more than others, bleed heavily during dental work, or have unusually heavy periods.
Hemophilia is rarer and more severe, involving deficiencies in specific clotting factors. A family history of unusual bleeding or bruising is one of the strongest clues that an inherited disorder is involved.
When Bruising Could Signal Cancer
Bruising is occasionally an early sign of a blood cancer like leukemia, lymphoma, or myeloma. These cancers disrupt normal blood cell production in the bone marrow, leading to low platelet counts. The bruises themselves look ordinary, but they behave differently: they keep forming in new places without any injury, and they tend to be flat.
A more specific warning sign is petechiae, tiny red spots that cluster together like a rash, typically on the lower legs, feet, and buttocks. These pinpoint dots indicate that platelet counts have dropped low enough that the smallest capillaries are leaking. Patients with blood cancers also commonly notice petechiae where pressure has been applied, such as where a blood pressure cuff was placed.
Bruising associated with cancer is almost always accompanied by other symptoms: persistent fatigue, unexplained fevers, night sweats, unintentional weight loss, or swollen lymph nodes. Bruising alone, without these additional signs, is unlikely to be cancer.
Patterns Worth Paying Attention To
Not all bruising warrants concern. A bruise larger than 1 centimeter that appeared without any trauma is considered clinically notable. Beyond size, the pattern matters. Bruises that appear in unusual locations, like the torso, back, or face rather than arms and shins, deserve more scrutiny than the ones on your legs from bumping into furniture.
Several specific combinations point toward a problem that needs investigation:
- Bruises plus tiny red dots (petechiae): suggests a platelet problem, whether from medication, bone marrow issues, or an autoimmune condition destroying platelets
- Bruises plus heavy bleeding: nosebleeds that won’t stop, very heavy periods, or prolonged bleeding from cuts suggest a clotting factor deficiency
- Bruises plus fatigue and weight loss: raises concern for blood cancers or serious systemic illness
- Bruises in a child who isn’t yet mobile: always requires medical evaluation
What Testing Looks Like
If your bruising is significant enough to investigate, the initial workup is straightforward blood testing. A complete blood count reveals whether your platelet count is normal. Clotting time tests measure how long it takes your blood to form a clot, which can identify problems with clotting factors. If those come back normal, more specialized tests of platelet function can pick up conditions like von Willebrand disease that basic tests miss.
For most people who bruise easily, test results come back normal. The bruising turns out to be caused by a medication, supplement, or simply the combination of thinner skin and minor impacts throughout the day that go unnoticed. That’s reassuring, even if it doesn’t make the bruises disappear.