Bisoctrizole

Bisoctrizole (INN/USAN, marketed by BASF as Tinosorb M and by MPI as Milestab 360, INCI methylene bis-benzotriazolyl tetramethylbutylphenol) is a benzotriazole-based organic compound that is added to sunscreens to absorb UV rays.

Bisoctrizole is a broad-spectrum ultraviolet radiation absorber, absorbing UVB as well as UVA rays. It also reflects and scatters UV. Bisoctrizole is a hybrid UV absorber, the only organic UV filter produced and microfine organic particles (< 200 nm), like microfine zinc oxide and titanium dioxide. Where other organic UV absorbers need to be dissolved in either the oil or water phase, bisoctrizole dissolves poorly in both.

Bisoctrizole is added to the water phase of a sunscreen as a 50% suspension, whereas mineral micropigments are usually added to the oil phase. The bisoctrizole particles are stabilized by the surfactant decyl glucoside.

Bisoctrizole shows very little photodegradation and has a stabilizing effect on other UV absorbers, octyl methoxycinnamate (octinoxate) in particular.

When formulated into a sunscreen, bisoctrizole has minimal skin penetration. Unlike some other organic sunscreen actives, it shows no estrogenic effects in vitro.

Bisoctrizole is not approved by the U.S. Food and Drug Administration (FDA), but is approved in the EU and other parts of the world.