It is hard to say what may have caused the bruise without seeing it and the surrounding skin. A bruise is formed when blood comes out of the smallest blood vessels into the surrounding connective tissue. Within approximately 7 days the blood is decomposed and the color of the bruise turns from dark blue to dark red, greenish, yellowish, and finally disappears.


If the bruise persists there is a possibility that the blood keeps on coming out from blood vessels in the vicinity. This might be possible if there is hemangioma beneath the skin surface. Hemangioma is a benign tumor that is formed of small capillaries. They are more susceptible to damage than regular blood vessels, which might be the reason for the blood loss, presented furthermore as a bruise.


You might want to visit a dermatologist who might be able to see the bruise and identify a possible hemangioma. If hemangioma is confirmed the dermatologist might recommend surgically removing it for cosmetic causes. Otherwise, hemagiomas are considered benign tumors and do not cause any harm unless they turn into a malignant tumor, which you might prevent with regular check-ups by a dermatologist.