Why do I bruise so easily? Causes, red flags and the blood tests that sort it out

Most unexplained bruises on the shins come from everyday bumps on skin that marks more easily than it used to. Bruises with an obvious place and cause behave differently from bruises on the back or belly with no injury, or bruising that comes with nosebleeds, bleeding gums or heavy periods. A blood test can explain the second group, and even then a normal first round of tests does not always close the question.

Unexplained bruising: when to get help now

Those other symptoms have their own pages: night sweats, unexplained weight loss and fatigue. Bruising together with any of them is a reason for a same-week appointment and a blood count.

What a bruise is, and how long it should last

A bruise is blood that has leaked from small vessels into the tissue under unbroken skin. It turns red-blue, then green, then yellow-brown as the body breaks the blood down and clears it. Most bruises fade in about two weeks; on the lower legs and in older, thinner skin, three weeks is common. A bruise still growing after a few days, or one that has not faded after a month, is worth showing to a clinician.

Color cannot date a bruise. A systematic review of studies in children found that clinicians judging bruise age from color were inaccurate, and that yellow was the only color with any link to age, and even then not a reliable one ⁶. Two bruises from the same day can look different on different parts of the body.

Where your bruises are tells you a lot

The common causes a blood test won't show

Aging skin is the biggest single cause. Collagen thins, the fat layer shrinks and vessels lose support, so a bump that once left nothing now leaves a patch. Years of sun speed this up on the forearms and hands; actinic purpura is common after 50 and becomes more common with each decade. Blood tests are normal in actinic purpura and in purpura simplex, which is why a full set of normal results in someone with only shin or forearm bruising is the expected answer.

Medicines come next ¹. Anticoagulants (warfarin, apixaban, rivaroxaban) slow clotting; antiplatelets (aspirin, clopidogrel) and NSAIDs such as ibuprofen stop platelets sticking; corticosteroids thin the skin, including high-dose inhalers and strong creams used for months. SSRI and SNRI antidepressants lower the serotonin platelets need to clump, and the bruising risk is highest when they are combined with an NSAID or a blood thinner. Regular heavy alcohol use lowers platelet counts and damages the liver. Ehlers-Danlos syndromes, inherited connective tissue conditions, cause easy bruising with stretchy skin and loose joints, and are diagnosed mainly by examination and family history, sometimes with genetic testing, rather than by a routine blood test.

For most supplements the bleeding risk on their own is small. The NIH fact sheets flag the combination instead: omega-3s ⁹, vitamin E ¹¹ and ginkgo ¹⁰ can add to the effect of warfarin or other blood thinners, which is why they belong on the list you give a prescriber.

Supplements people ask about with bruising

Weak bleeding signalOmega-3At usual doses the effect on bleeding is small, but it can add to warfarin. If you take a blood thinner, mention it to the prescriber.In our shop

TheoreticalTurmericCurcumin affects platelets in lab studies; the real-world concern is combining it with a blood thinner.In our shop

Early evidenceNattokinaseAn enzyme that breaks down fibrin; worth flagging to a prescriber if you also take an anticoagulant.In our shop

The causes a blood test can find

Low platelets

Platelets plug small vessel leaks within minutes. A low platelet count (thrombocytopenia) can follow a viral infection, heavy drinking, low B12 or folate, an enlarged spleen from liver disease, a medicine, lupus, or immune thrombocytopenia (ITP), where the immune system clears platelets. ITP is defined as a platelet count under 100 x10^9/L with no other cause found ⁷. Rarely, a low count is the first sign of a marrow disease such as leukemia, which usually also shifts the white cells or hemoglobin on the same CBC. The low platelet count page covers the causes in depth, and B12 deficiency and pernicious anemia explain the marrow link.

Von Willebrand disease

Von Willebrand disease is the most common inherited bleeding disorder. Low von Willebrand factor levels turn up in up to about 1% of people in lab surveys, while symptoms bad enough to reach a clinic affect around 1 in 1,000 ². Von Willebrand factor is the glue that holds platelets to a damaged vessel wall, so the bleeding shows up in the skin and the lining of the nose, mouth and womb: easy bruising, long nosebleeds, heavy periods and bleeding after dental work. Many women with von Willebrand disease are first noticed because of heavy periods, iron deficiency and anemia.

Liver disease

The liver makes most clotting factors. In cirrhosis, lost clotting factors raise the INR, and an enlarged spleen traps platelets and lowers the count. The liver also makes less of the body's natural anticoagulants, so the balance shifts in both directions and a raised INR in chronic liver disease does not reliably predict bleeding ⁵. Clotting changes appear once fatty liver or alcohol has progressed to cirrhosis; fatty liver is the common route there in the US.

Kidney disease

In advanced chronic kidney disease, waste products that the kidneys normally clear make platelets less sticky, so people bruise with a normal platelet count ¹. An eGFR on a routine panel shows how far kidney function has fallen; the chronic kidney disease page reads the stages.

Vitamin C and vitamin K deficiency

Vitamin C builds the collagen that supports small vessels. Scurvy, severe vitamin C deficiency, causes bruising, bleeding gums, bleeding around hair follicles and corkscrew-shaped body hairs, usually in people eating very few fruits and vegetables, people who drink heavily, and people on very restricted diets ⁴.

Vitamin K is needed to finish making several clotting factors. Deficiency is rare in healthy adults and shows up with malabsorption (celiac disease, bowel surgery, cystic fibrosis), long antibiotic courses or very poor intake. Clinicians usually assess vitamin K status through the prothrombin time rather than a direct blood level ⁸.

Which blood tests to ask for, and how to read them

The American Family Physician review of bruising in primary care puts a structured bleeding history first, then a complete blood count (CBC) with platelet count and blood smear, prothrombin time (PT/INR) and activated partial thromboplastin time (aPTT), with fibrinogen often added ¹. A liver panel (ALT, albumin) and kidney panel (creatinine, eGFR) are added when the history points that way, and ferritin when periods or other bleeding are heavy. The clotting tests explainer and the CBC explainer go through every line of those reports.

Platelet counts between 150 and 450 x10^9/L are typical. That unit is the same number your report may show as K/uL or thousand per microliter: 120 means 120,000 platelets in each microliter. Bleeding after injury or surgery becomes more likely under about 50, and spontaneous bruising and petechiae usually appear only under 20 to 30 ³. A mildly low count is often rechecked within a few weeks, sooner if new bruising or pinpoint spots appear, because one reading says less than a trend. A normal count with bruising points away from platelet numbers and toward platelet function, von Willebrand factor or the skin.

An untreated person's INR sits around 1.0; on warfarin the usual target is 2.0 to 3.0, so a person on warfarin will bruise more with an INR in range. Von Willebrand testing needs the antigen, an activity assay and factor VIII together, and von Willebrand factor levels run lower in blood group O and rise with stress, exercise, inflammation, pregnancy and estrogen-containing pills. One normal von Willebrand result does not rule the disease out, and repeat testing is common ². Ferritin belongs on the list as a measure of what heavy periods or other bleeding have cost; the iron studies explainer reads it.

Is my bleeding history normal? A quick self-check

Hematologists score bleeding history with a standard bleeding questionnaire, the ISTH-BAT (from the International Society on Thrombosis and Haemostasis), and the 2021 von Willebrand guideline recommends a validated tool like it as the first screen ². The formal score is done by a clinician (abnormal is 4 or more in adult men and 6 or more in adult women), but the questions themselves are a useful self-check.

• Nosebleeds that last more than 10 minutes or have needed medical treatment
• Bruises larger than 1 cm, in several places, with no injury you can recall
• Bleeding for hours after a tooth extraction, or needing stitches or packing
• Heavy periods: flooding, changing a pad or tampon every 1 to 2 hours, clots larger than about 2.5 cm, or iron deficiency from periods
• Bleeding after surgery or childbirth that needed a transfusion or a second operation
• A parent, sibling or child with a diagnosed bleeding disorder

What helps, once the serious causes are out

For actinic purpura and thin skin, daily sun protection on the forearms and hands slows further damage, and a moisturizer keeps skin less prone to tearing. Long sleeves and padding sharp furniture edges reduce the bumps that start bruises. A cold compress in the first day and raising a bruised leg limit how far the blood spreads.

Vitamin C from food covers most people: the recommended intake is 90 mg a day for men and 75 mg for women, with 35 mg extra for smokers. A medium orange has about 70 mg, a kiwi about 64 mg and half a cup of raw red pepper about 95 mg ⁴. A vitamin C supplement corrects bruising and gum bleeding caused by deficiency, but there is no evidence it helps bruising when levels are normal, so it matters mainly for people with a confirmed low level or a very restricted diet.

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