A bruise forms when a bump or impact breaks tiny blood vessels under the skin without cutting the surface. Blood leaks into nearby tissue, creating a colored mark that can feel sore or tender. Bruises matter because they show how the body responds to injury and repairs damaged tissue.
Most bruises heal on their own, but large, painful, or unexplained bruises can signal a medical problem.
Key Facts
- A bruise is also called a contusion.
- Bruises form when capillaries rupture and blood leaks into tissue under the epidermis.
- Typical color order: red, purple or blue, green, yellow, then fading brown.
- Hemoglobin in trapped red blood cells breaks down into pigments such as biliverdin and bilirubin.
- Most small bruises heal in about 10 to 14 days.
- Cold packs can reduce early swelling by narrowing blood vessels, while gentle warmth later can help blood flow and healing.
Vocabulary
- Epidermis
- The epidermis is the thin outer layer of skin that protects the body from the environment.
- Dermis
- The dermis is the skin layer beneath the epidermis that contains nerves, blood vessels, sweat glands, and connective tissue.
- Capillary
- A capillary is a tiny blood vessel where oxygen, nutrients, and waste move between blood and body tissues.
- Hemoglobin
- Hemoglobin is the iron-containing protein in red blood cells that carries oxygen and gives blood its red color.
- Inflammation
- Inflammation is the body's protective response to injury, often causing redness, warmth, swelling, and pain.
Common Mistakes to Avoid
- Thinking a bruise means the skin surface must be cut is wrong because bruises usually happen under unbroken skin when capillaries leak blood.
- Assuming bruise colors are random is wrong because the colors follow chemical changes as hemoglobin breaks down during healing.
- Putting heat on a fresh bruise right away is often a mistake because heat can increase blood flow and may worsen early swelling or pooling.
- Ignoring large, very painful, or unexplained bruises is unsafe because they can sometimes point to a fracture, bleeding disorder, medication effect, or other health issue.
Practice Questions
- 1 A bruise appears blue-purple on day 2 and fades to yellow by day 10. How many days passed between those two observations?
- 2 A student has a bruise that usually heals in 14 days. If the bruise formed on March 3, on about what date would you expect it to be mostly healed?
- 3 Explain why a bruise can change from red to purple to green to yellow even though no new injury has happened.