Here’s Why You Bruise So Easily

Whether you remember the exact moment you stubbed your poor little toe on the corner of that coffee table or you just woke up with an eye-catching, unexplained new black-and-blue spot on your thigh, bruises often carry a bit of mystery with them. Since they don't always show up immediately after the bump in question, sometimes it seems like bruises appear out of nowhere — and like we're getting way more of them than our fair share. So what's the deal? Why do some people bruise more than others?

A bruise is simply "an injury to the soft tissue in the skin that causes blood to leak out of the blood vessels into the skin, which causes the skin to turn funny colors," says Roy Silverstein, MD, of the Medical College of Wisconsin Division of Hematology and Oncology. But some of us really are more susceptible to bruises than others. Here are a few factors that Dr. Silverstein says might play a role in your bruise vulnerability:

As we get older, the tissue around our blood vessels gets thinner and our skin gets thinner," says Dr. Silverstein. "So we’re more susceptible to having an injury to that blood vessel, because the skin isn’t as strong or elastic as it is when we’re younger." Less strength, elasticity, and protection equals more bruises.

Even if you're still a spring chicken, pretty much anything that prematurely ages the skin will cause the same vulnerability. That includes smoking and hanging out in the sun for too long. So there's yet another reason to limit your tanning time.

Surprise! Some medications can thin your skin too, making you more susceptible to the ol' black-and-blues. The most common culprits are corticosteroid medications, which are used for inflammatory diseases and asthma, says Dr. Silverstein.

Although vitamin deficiencies can cause you to bruise more easily, it's pretty unlikely that's what's happening. "Vitamin C deficiency — scurvy — causes this; vitamin D deficiency can also cause this," Dr. Silverstein says, "but we don’t really see this any more. Most people in countries like the United States don’t have trouble getting enough vitamins in their diet." (Did you think vitamin D deficiency was super common? Turns out, that's debatable.)

There are some rare illnesses that cause bruising, but the keyword here is "rare." These include diseases that lower our blood's platelet count. "Platelets are tiny, little cells in our blood that help the blood to clot," says Dr. Silverstein. "So if the blood doesn’t clot normally, even a very minor trauma — you just brush your leg up against something, and you wouldn’t even notice it — can cause a bruise."

For instance, in idiopathic thrombocytopenic purpura (ITP), the body's antibodies attack those platelets, which can cause bruises. Easy bruising can also come with the abnormal development of the blood in leukemia. But Dr. Silverstein advises that the bruising in these cases is very obvious (you might have blood blisters in your mouth, for instance) and isn't usually the only reason to worry.

"If someone comes in and says they bruise easily, well, that’s not really that uncommon," says Dr. Silverstein. "But if someone comes in and their entire arm is covered in bruises or they’re getting bruises in areas where it would be very unusual to have an injury (like in the small of your back or the inside of your thighs), that would be something to worry about."

So for most bruises, just chill out and enjoy the weird, changing colors — and watch out for that coffee table.