A hematoma is an accumulation of blood outside the bloodstream or in the tissue or cavity. A hematoma is an effusion of blood into tissue or an anatomical cavity due to increased bleeding after an accident or operation. Bleeding into the subcutaneous connective tissue is visible through the skin as a so-called "bruise". Hemoglobin degradation in the phagocytes then produces green biliverdin, from which yellow bilirubin is subsequently formed by reduction. This explains the typical color change of a hematoma. The bruise turns brown-red, purple, green and finally yellow before disappearing. Hematomas can lead to serious complications, depending on their extent and, above all, their location.