Purple spots on the legs of AIDS patients are considered to be related to bumping injury, abnormal coagulation function, anaphylactic purpura, Kaposi’s sarcoma and so on. 1. Bumping injury: when AIDS patients’ legs are bumped by hard objects, it can be manifested as purple spots, and it is easy to be accompanied by pain, swelling and other uncomfortable symptoms. 2. Abnormal coagulation function: when AIDS patients lack coagulation factors, platelet abnormality, medication and other causes of abnormal coagulation function, it can be manifested as purple spots on the legs. Some patients may also suffer from other symptoms such as bleeding, dizziness and lack of concentration. 3. Anaphylactic purpura: When HIV patients suffer from infections caused by decreased immunity or allergic purpura induced by medication, it can also be manifested as purple spots on legs. Patients with purpura are also prone to joint swelling, restricted movement, abdominal pain and other uncomfortable symptoms. 4. Kaposi’s sarcoma: AIDS patients are susceptible to Kaposi’s sarcoma, which is commonly found in the oral mucosa, trunk and other parts of the body. The skin lesions start as pink and then darken to form a mauve or brown rash, which is manifested as purple spots on the legs. It is recommended that HIV patients with purple patches on the legs seek medical attention so that the cause of the disease can be determined and treatment can be prescribed.