You bump your leg on the coffee table, barely notice it, and two days later discover a purple-blue mark the size of a plum. Meanwhile, your friend walks into furniture constantly and rarely shows a mark. What gives?

Bruising isn't random, and it's not simply about being clumsy. The science behind why some people turn black and blue more easily involves a fascinating interplay of blood vessel strength, clotting chemistry, and sometimes the medications sitting in your medicine cabinet. Understanding your own bruising patterns can help you distinguish between normal variation and something worth mentioning to your doctor.

Bruises happen when tiny blood vessels called capillaries break and leak blood under your skin. But not everyone's capillaries are created equal. Think of these vessels like garden hoses—some are thick and sturdy, others are thin and prone to cracking under pressure.

Age is the biggest factor in capillary fragility. As we get older, the collagen supporting our blood vessels gradually breaks down, and the skin protecting them becomes thinner. This is why elderly people often develop bruises from the gentlest contact. Sun damage accelerates this process, which explains why bruises often appear more easily on forearms and hands that have had decades of UV exposure.

Genetics also plays a significant role. Some people inherit naturally thinner vessel walls or less supportive connective tissue. Women tend to bruise more easily than men, partly due to thinner skin and differences in how fat is distributed beneath it. Estrogen may also affect blood vessel walls, which is why some women notice increased bruising at certain points in their menstrual cycle.

Takeaway

If you've always bruised easily and it runs in your family, it's likely just your body's normal variation. But if your bruising pattern suddenly changes or worsens, that's worth discussing with your doctor.

When a capillary breaks, your body immediately launches a repair mission. Platelets—tiny cell fragments in your blood—rush to the scene and stick together to form a plug. Then clotting factors, a cascade of proteins, weave a mesh to reinforce this plug and stop further bleeding.

Variations in this system explain a lot about bruising differences. Some people have slightly fewer platelets or platelets that don't stick together as efficiently. Others may have subtle differences in their clotting factor levels. Most of these variations fall within the normal range and don't cause problems beyond easier bruising.

However, certain conditions can genuinely impair clotting. Vitamin K deficiency affects clotting factor production—this vitamin is essential for your liver to manufacture several key proteins. Liver disease can have similar effects since that's where clotting factors are made. Conditions like von Willebrand disease, which affects about 1% of the population, cause a specific clotting protein deficiency that leads to easier bruising and bleeding.

Takeaway

Bruises that seem disproportionate to the injury, appear in unusual locations, or come with other bleeding symptoms like frequent nosebleeds or heavy periods may signal a clotting issue worth investigating.

That daily aspirin or ibuprofen you take without much thought might be the biggest factor in your bruising. Blood thinners and anti-inflammatory drugs are remarkably effective at turning minor bumps into major bruises.

Aspirin and NSAIDs like ibuprofen work by interfering with platelet function. Even a single aspirin can affect your platelets for their entire seven-to-ten-day lifespan. Prescription blood thinners like warfarin or the newer direct oral anticoagulants go further, actively suppressing your clotting cascade. Fish oil supplements, vitamin E in high doses, and even some herbal remedies like ginkgo can have similar effects.

The tricky part is that these effects are cumulative and often unexpected. Someone taking a baby aspirin for heart protection, fish oil for cholesterol, and occasional ibuprofen for headaches might be significantly impairing their clotting without realizing it. Alcohol adds another layer—it both affects platelet function and can thin the blood temporarily. If you're noticing more bruising than usual, your medication and supplement list is the first place to look.

Takeaway

Before worrying about mysterious bruising, inventory everything you're taking—including supplements and occasional pain relievers. Bring this complete list to your doctor, as the combination often matters more than any single item.

Bruising is your body's visible story of minor injuries meeting your unique biology. The combination of your blood vessel strength, clotting efficiency, and anything affecting these systems creates your personal bruising fingerprint.

Most easy bruising is simply normal variation—inconvenient but harmless. The key is knowing your own pattern and noticing when something changes. When in doubt, a simple blood test can check your platelet count and basic clotting function, offering reassurance or catching something that needs attention.