The slowest time for a big bag to disappear after a fall on the forehead depends on the situation of the fall, measures and other factors, and cannot be generalized. If the patient has headache, dizziness, nausea, vomiting or local pain, he/she should go to the emergency department or neurology department and have a CT examination of the head for clarification. If the above cases are excluded, consider that the large forehead bag is a subcutaneous hematoma. Because of the rich subcutaneous blood transport of the head and face, the fall will lead to subcutaneous vascular damage, followed by bleeding, resulting in a subcutaneous hematoma, which can usually be absorbed by itself in 2-3 weeks. If the hematoma does not subside on its own for more than 1 month, it needs to be treated by a professional physician with puncture, aspiration and pressure bandaging, and the hematoma will gradually disappear after 2-3 treatments. Within 24 hours after the fall, the patient can use a towel wrapped in ice to apply local ice, which can inhibit the expansion of the hematoma and also reduce the pain to a certain extent.