The causes of hematuria include the following: 1. The stones are combined with infection of the surrounding tissues, which can cause erosion and congestion of the surrounding mucosa, and bleeding can occur. 2. Stones can repeatedly rub against the mucosa, causing mechanical damage to the mucosa, resulting in mucosal rupture and bleeding, such as excessive friction between stones and the mucosa of the renal pelvis during strenuous activity, resulting in local mucosal rupture, which can lead to red urine after exercise. After stopping strenuous exercise and taking moderate rest, the hematuria can be gradually relieved. However, sometimes walking or light physical labor may also lead to mechanical friction between the stone and the mucosa, which means that the patient is not engaged in strenuous activities, and this bleeding may also occur.