The bleach-like smell in semen comes primarily from a compound called spermine, a polyamine found in seminal fluid. Spermine itself is relatively odorless when fresh, but when it oxidizes on contact with air, it breaks down into compounds that smell remarkably similar to chlorine bleach. This isnโt a coincidence or a loose comparison. The chemical reaction that produces the smell belongs to the same family of oxidation processes in both cases, which is why the comparison lands so accurately that it has its own distinct recognition in clinical literature.