When you bang a part of your body against something, your skin might turn different colors where you bumped it. That splotch of purple, green, blue, and black is called a bruise, and it's caused by blood leaking from broken blood vessels (the tubes that contain blood) under your skin. Because you didn't cut yourself, the blood from the damaged blood vessels can't come out and instead gets trapped under the skin. A bruise may look icky, but your body will make it disappear in no time!
Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
© 1995-2013 The Nemours Foundation/KidsHealth. All rights reserved.