Ejaculation
When a man is stimulated, his penis becomes erect. When he has an orgasm, semen comes out from the end of his penis. Semen contains sperm and other substances. How long a man can be stimulated before ejaculating, how long the ejaculation lasts, the strength of the ejaculation, and the amount of semen that comes out, all vary from one man to another. Ejaculation can also happen without control when a man is sleeping. Boys do not ejaculate until they reach puberty.