How do I know if I'm ejaculating semen?
There are three fluids which comes from a man's penis: urine, pre-ejaculate, and semen. Urine is a yellow-tinted clear liquid. Pre-ejaculate is clear with no tint, is a bit thicker than urine and feels slick to the touch. Semen is even thicker. It is white to whitish-yellow in color and is not transparent.
In the design of the male body, it is not possible for urine to flow from the bladder when you are sexually aroused. There are muscles in the prostate gland, just below your bladder, which act in a manner similar to a railroad switch. Either the pathway to the bladder is open or the pathway to the ejaculatory duct, but not both at the same time.
Thus, when a guy is sexually aroused, which is evident by having an erect penis, touching and rubbing the genitals and other areas of the body causes the body to eventually ejaculate semen with an intense pleasurable feeling that is called orgasm. This can happen in your sleep, which is called a wet dream. Even if you don't remember having the wet dream, you will know you ejaculated semen because there will be semen on your shorts or bed clothes. When semen dries on cloth, it becomes very stiff and leaves a stain, which fortunately washes out easily.
Children cannot ejaculate semen. The ability to produce semen comes in either stage 2 or stage 4 of development. About half of all boys start producing semen in stage 2 and the rest start in stage 4.
Pre-ejaculate fluid comes from a different set of glans which develop separately from the glands which produce semen. Pre-ejaculate drips out of your penis when you are sexually aroused. You don't even need to have an erection to drip pre-ejaculate fluid. Some guys start producing pre-ejaculate fluid before they produce semen, others start producing pre-ejaculate fluid after they start producing semen.