Unexplained bruising usually comes down to one of a handful of causes: medications that thin the blood or weaken the skin, nutritional gaps, age-related skin changes, or less commonly, an underlying condition affecting how your blood clots. Most of the time, the explanation is straightforward and fixable. But bruising that’s frequent, large, or accompanied by other bleeding symptoms can signal something that needs medical attention.
Medications and Supplements
This is one of the most common and most overlooked causes of easy bruising. Several categories of everyday drugs interfere with your blood’s ability to clot or make your skin more fragile. Over-the-counter pain relievers like aspirin, ibuprofen, and naproxen all reduce platelet function, which means even minor bumps you don’t remember can leave visible marks. Prescription blood thinners, including warfarin, apixaban, and rivaroxaban, have an even stronger effect.
Antidepressants, particularly SSRIs, and some antibiotics can also interfere with clotting. Corticosteroids, whether taken orally or applied as a cream over long periods, thin the skin itself, making blood vessels closer to the surface and easier to damage. If you’ve recently started or changed any medication and notice more bruising, that connection is worth exploring with your prescriber.
Supplements play a role too. Ginkgo biloba, garlic supplements, and omega-3 fatty acids (fish oil) all have documented blood-thinning effects. Taken alone the effect is mild, but combined with each other or with medications like aspirin, they can meaningfully increase bruising.
Aging and Sun-Damaged Skin
If you’re over 60 and noticing purple blotches on your forearms or the backs of your hands, you’re likely dealing with a condition called senile purpura (sometimes called actinic purpura). It happens because years of sun exposure and natural aging break down the connective tissue in the skin. The skin and the tissue underneath it become thinner, and the small blood vessels beneath lose their structural support. A bump that wouldn’t have left a mark at 30 can cause a dramatic bruise at 70. These bruises are harmless, though they can take longer to fade. They’re especially common on areas that have had the most lifetime sun exposure.
Vitamin Deficiencies
Your body needs specific nutrients to maintain strong blood vessels and form clots. Two of the most important for bruising are vitamin C and vitamin K.
Vitamin C is essential for building collagen, the protein that gives blood vessel walls their strength. When you don’t get enough, those walls become fragile and leak more easily. Severe deficiency (scurvy) is rare in developed countries, but mild deficiency is not, especially in people with limited diets, smokers, or those with digestive conditions that reduce absorption.
Vitamin K is the nutrient your body needs to form blood clots. Without adequate vitamin K, even small vessel injuries bleed longer under the skin. Adults with poor dietary intake, those on long-term antibiotics (which can kill gut bacteria that produce vitamin K), or people with fat absorption problems are most at risk.
Liver Disease
The liver manufactures nearly all of the proteins your blood needs to clot. When liver function declines, whether from chronic alcohol use, hepatitis, fatty liver disease, or cirrhosis, the production of these clotting proteins drops. Clotting factor levels generally fall in parallel with the progression of liver disease. The liver also produces thrombopoietin, a hormone that drives platelet production, so liver damage can lead to lower platelet counts as well. Up to 76% of people with cirrhosis develop reduced platelet levels to some degree.
Easy 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 dark-colored urine. But unexplained bruising can be an early signal before more obvious symptoms develop.
Bleeding and Clotting Disorders
When bruising is disproportionate to any injury, or when it’s accompanied by frequent nosebleeds, heavy periods, or bleeding gums, a clotting disorder becomes a more likely explanation.
Von Willebrand disease is the most common inherited bleeding disorder. It affects a protein that helps platelets stick together and form the initial plug at the site of a vessel injury. Many people with mild forms don’t get diagnosed until adulthood, often after noticing a pattern of easy bruising, prolonged bleeding from cuts, or unusually heavy menstrual periods.
Low platelet counts (thrombocytopenia) can result from many things: autoimmune conditions where the body destroys its own platelets, bone marrow problems, or certain infections. In rare cases, unexplained bruising combined with fatigue, recurrent infections, or bone pain can point to leukemia or other bone marrow cancers that crowd out normal platelet-producing cells.
Autoimmune and Vascular Conditions
Sometimes what looks like a bruise is actually a sign of blood vessel inflammation, known as vasculitis. The key difference: standard bruises are flat and painless to the touch, while vasculitis-related marks (called palpable purpura) feel slightly raised or bumpy when you run a finger over them. They tend to cluster on the lower legs and don’t blanch when you press on them.
One well-known form, IgA vasculitis (formerly called Henoch-Schönlein purpura), affects small blood vessels and can involve the skin, joints, gut, and kidneys. Lupus and other autoimmune diseases can also trigger bruising through multiple pathways, including platelet destruction and blood vessel damage.
Strenuous Exercise
Intense physical activity, particularly bodybuilding and long-distance running, can cause bruising even without direct impact. During strenuous exertion, especially in warm weather, the temperature regulation system in working muscles can break down, leading to sluggish blood flow and eventual inflammation and injury to small blood vessels. This is more of a nuisance than a health concern, and the bruising typically resolves on its own within a few days of rest.
Bruising Patterns Worth Paying Attention To
Not all unexplained bruising warrants worry, but certain patterns do. You should bring it up with a healthcare provider if you notice bruises that last more than two weeks, frequent large bruises without clear cause, a lump forming inside a bruised area, or a bruise that keeps recurring in the same spot. Bruising alongside other unusual bleeding, such as blood in your urine or stool, nosebleeds that are hard to stop, or bleeding gums, raises the concern that a clotting problem may be involved.
The initial evaluation is usually straightforward: a complete blood count to check platelet levels, and clotting time tests to see how quickly your blood forms a clot. If those come back normal but suspicion remains, testing for von Willebrand disease and platelet function is the typical next step. If clotting times are prolonged, liver function and vitamin K status are checked. These tests, taken together, can narrow down the cause in the large majority of cases.