— § 01
What bemotrizinol actually is.
Bemotrizinol — sold as Tinosorb S — is a triazine-class organic sunscreen filter introduced by BASF in the early 2000s. It absorbs across UVB and the entire UVA range with a long-wavelength tail past 380 nm, an area where almost every older organic filter loses coverage. It is also photo-stable: it does not degrade meaningfully under sunlight, and it stabilises companion filters that do (most importantly, avobenzone).
In short, it solves the three failure modes of the 1990s sunscreen palette: incomplete UVA coverage, photo-degradation, and the white cast of mineral alternatives. It is the closest thing to a perfect single chemical filter the market has produced.