What Is Semen Actually Made Of?
A quick, factual answer: semen is mostly fluid from the seminal vesicles and prostate gland, with sperm cells making up a surprisingly small fraction of the total volume.
The actual composition
Roughly 60–70% of semen volume comes from the seminal vesicles, contributing fluid containing fructose (which fuels sperm motility) and other proteins. About 20–30% comes from the prostate gland, contributing enzymes and other components that help with sperm function and semen consistency. Sperm cells themselves make up a small fraction of total volume — typically well under 5%. The remainder includes fluid from other glands along the reproductive tract.
Why this comes up in STD-adjacent conversations
Semen can carry several STDs, including HIV, gonorrhea, chlamydia, and others, which is the actual health-relevant point buried under a lot of unrelated internet claims about semen's composition and supposed effects. Semen composition itself has no bearing on STD risk one way or the other — that's determined by whether an infection is present, not by any property of the fluid itself.