A bruise happens when tiny blood vessels under the skin break from an impact, leak blood into nearby tissue, and that trapped blood shows through the skin as a dark patch.

What a bruise actually is

  • A bruise is bleeding inside the tissue without an open cut, called a subcutaneous hematoma.
  • The leaked blood pools under the skin and creates the familiar blue‑purple discoloration.

Main immediate cause

  • Most bruises come from direct trauma: bumping into furniture, falls, sports impacts, or minor accidents that crush small vessels.
  • Even when the hit feels small, enough force on soft tissue can still burst capillaries and cause a visible mark.

Why some people bruise easily

  • Fragile blood vessels or thinner skin (common with aging or low estrogen in menopause) make vessels easier to damage.
  • Low platelets or clotting problems (like hemophilia or von Willebrand disease) mean bleeding lasts longer, so bruises look larger and more frequent.
  • Certain medicines (blood thinners, aspirin, steroids) and conditions like leukemia can also increase bruising.

Role of vitamins and hormones

  • Lack of vitamin C, vitamin K, or vitamin B12 can weaken vessels or clotting, so small bumps lead to more bruises.
  • Hormonal changes, especially reduced estrogen in women, can thin and weaken the skin and vessels, increasing bruising on arms and legs.

Why the color changes

  • Right after injury, oxygen‑rich blood makes the bruise look red or purplish.
  • As the body breaks down the trapped blood, it shifts from blue‑purple to green and yellow before fading as the blood is reabsorbed.

Information gathered from public forums or data available on the internet and portrayed here.