2. Why is this happening at night? This is the result of the action of androgen. When a man reaches puberty, androgen will stimulate the testis to continuously produce semen and store it in the seminal vesicle. When the storage of seminal vesicle reaches a certain level, it will send a signal to the brain, and the semen needs to be discharged when it is full. When a man does not have a suitable sexual partner or it is inconvenient to get married, semen may flow involuntarily. There is no need to worry about this situation. If life is troubled, you can go to urology, have regular prostate and seminal vesicle examinations, and take anti-inflammatory and detumescence drugs, which can achieve satisfactory results.