It happens when he has an orgasm.
Semen leakage or any other concerns related to your reproductive system should be discussed with your primary doctor or a urologist. Some boys are scared when this happens - and they worry that other people will see the swelling. How do I choose a urologist to evaluate my situation and perform procedures if necessary? Wet dreams Around the time of puberty most boys start having 'wet dreams'. Penis size As boys grow through puberty and into young manhood their penis gets longer and thicker. When a boy starts to ejaculate, he usually produces only a small amount of semen. If surgery on your prostate or pelvic area resulted in ejaculation changes, this may be more difficult to treat.