Purpura and bruising are both skin changes caused by subcutaneous bruising, they have differences in etiology, symptoms and treatment methods, the specific differences are as follows: 1, etiology: purpura is formed by the rupture of subcutaneous capillaries, it is a pathological disease, including simple purpura, allergic purpura and thrombocytopenic purpura, it will not disappear naturally. The bruises are mostly formed by external force causing subcutaneous bleeding and will disappear slowly over time; 2. Symptoms: purpura is mostly bleeding spots between 3-5mm in diameter, with clear borders and slight itching, more often in the lower limbs and buttocks, symmetrically distributed, beginning to appear as red papules above the skin surface, slowly fusing into flakes, and will not fade when pressed by hand. The bleeding point of bruising is usually above 5mm, with irregular edges, mostly in the parts of the body that are prone to external collision such as knee and shin front, which are flat with the skin and have obvious pain when pressed; 3. Treatment: purpura is more serious compared to bruising, which requires timely consultation and systematic treatment, while the bruising caused by external collision can be treated by itself, such as choosing to apply hot towels to accelerate the absorption of bruising. If subcutaneous bruising occurs without any obvious cause, it is impossible to identify whether it is purpura or bruising, it is recommended to consult a doctor promptly to clarify the specific cause, exclude the coagulation abnormalities and treat the problem symptomatically to avoid delaying the condition.