The smell of urine in the exhaled gas usually comes from urea or amines, etc. It may be due to severe renal impairment, gastrointestinal bleeding and other reasons. 1. Severe renal impairment: When severe renal impairment or uremia occurs, there may be little or no urine, resulting in the body of urea and amines can not be excreted from the urine, but only with the respiration out of the body, the exhaled gas urine odor. It is recommended to go to the hospital in time. 2. Gastrointestinal bleeding: after gastrointestinal bleeding, red blood cells and other plasma components are metabolized into ammonia-smelling substances in the gastrointestinal tract, which are absorbed into the blood in the intestines and may be excreted through the lungs, resulting in the smell of urine in the exhaled gas. It is recommended to go to the hospital in time.