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What are Bruises?

Learn why bruises form, when they are a sign to seek medical help, and why they itch.

By
Rob Lamberts, MD,
December 22, 2009
Episode #003

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What are Bruises?

A reader named Emily recently asked me the following:

“Dr. Rob, can you tell me about bruises?   What should I do when I get one? And why do they itch? I’ve always wondered about that.”

The medical term for a bruise is hematoma. Bruises happen when part of the body encounters blunt trauma. You can find good examples of blunt trauma every week on the popular TV show America’s Funniest Videos. On the show, people receive blunt trauma in amazing ways and usually in very unfortunate places. Doctors call blunt trauma to the human body a contusion. AFV is accurate, though, as scientists estimate that 25% of all contusions happen when people stand too close to a piñata.

What Causes Bruises?

So what happens after the cameras stop rolling? The blunt trauma to the unfortunate body causes small blood vessels under the skin to break, letting the blood seep into the surrounding tissue.

Before moving on, I need to mention that that bruises don’t just happen to the skin. You can bruise a bone, your liver, or your brain. The mechanism is the same, blunt trauma leading to blood seeping into the tissue of one of these organs, but it can obviously be more serious. It also has a better chance of winning the $10,000 prize.

So what happens after the blood seeps into the soft tissue? The red blood cells break and spill their insides out into the surrounding tissue. The most significant substance from inside the red blood cells is called hemoglobin. Hemoglobin is the protein that makes blood red. In the bloodstream, it binds to oxygen and carries it from the lungs to the parts of your body that need it. Hemoglobin that is bound to oxygen is bright red, and turns darker and bluish in color when it loses the oxygen. That is why the veins under your skin are blue -- they are the thinner-walled blood vessels that take the blood back to the lungs after the oxygen is taken off.

Why Do Bruises Hurt?

When the red blood cells break open, they release substances that signal the body to bring in the white blood cells. The white blood cells are the paramedics of the body, but instead of using teeny little stretchers, they actually eat the hemoglobin and other things let out by the broken red blood cells. Any paramedics listening to this podcast shouldn’t get any ideas from this. The white blood cells then release more substances that cause the swelling and redness known as inflammation.

Inflammation is what makes the bruise hurt so dang much. The redness and swelling are from the increased blood flow that occur to speed the healing. The pain serves to remind the injured person to steer clear of situations that could cause additional trauma.

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