The forehead becomes full, if there is impacted by external force, it may be a sign of hematoma. If there is no impact by trauma, suddenly become full, it may be a sign of disease, mostly related to kidney disease. 1, hematoma: forehead unintentionally impacted or squeezed, may damage the local soft tissue, and even lead to capillary rupture bleeding, hematoma, forehead may appear swollen, and thus become more full. Generally with time, hematoma or edema usually absorbs on its own. If it is too full, you can also apply cold compresses locally to reduce blood exudation and help reduce swelling; 2, kidney disease: such as acute nephritis, chronic nephritis and kidney failure, it will cause generalized swelling, which may also be manifested as forehead swelling and the formation of a full state. This is because the main function of the kidneys is to excrete metabolic products in the human body, such as excreting excess water in the body of origin. If the kidneys function abnormally, the water cannot be excreted out of the body and may accumulate in the body and cause swelling, which usually requires further examination in the hospital to clarify the cause and then treatment. It is recommended to go to the hospital for a detailed examination to clearly diagnose the cause according to the symptoms of forehead fullness. Usually, you also need to pay attention to rest, maintain a good work and rest schedule, and do not stay up late. Try to take light, easy-to-digest food as much as possible, and eat more fresh fruits and vegetables.