Semen contains an estimated 6MG of protein per ejaculation. It is mostly Proteins and natural sugars an insignificant amount of vitamins and several hormones that help guide the semen and fertilize ovum. It's about as much protein as a bite of egg or a few bites of pork chop.
Semen is good for your skin. Sugars in semen make it easy for the skin to absorb while keeping the proteins active. The Protein repairs skin cells and improves elasticity, softening wrinkles and giving skin the healthy-glow. However skin lotions formulated to be absorbed readily containing lipids or aloe are more effective in this attempt.
Semen isn't used in any manufactured beauty product that I've heard of, but I've heard of more than one salon using bull semen to add shine and additional strength to hair.