What subject does purpura belong to?

You can choose hematology or immunology. Purpura refers to the color change of skin and mucosa after blood. The clinical manifestations are bleeding spots, purpura and ecchymosis, which are generally not higher than the skin surface. Only when allergic purpura occurs, it can be slightly raised, starting with purple, not fading after being pressed, then gradually becoming shallow, and turning yellow and fading after about two weeks. The diseases that cause subcutaneous hemorrhage are collectively called purpura, and most of them are allergic purpura (Scheer-Heinz disease) caused by vascular system disorder and primary thrombocytopenic purpura caused by thrombocytopenia.