Regarding skin pigmentation, the soybean extract works by hindering melanosome transfer, meaning it blocks the melanin pigment from traveling up to the surface of the skin and becoming visible there.
A sunscreen with BP-3 is definitely better than no sunscreen. However, if you find a formula that you love and contains BP-3, we do not think that you should throw it away. Overall, BP-3 is probably our least favorite sunscreen agent and we prefer sunscreens without it. It can be used in concentrations of up to 10% in the EU and up to 6% in the US. On the up side, sunscreens are pretty well regulated in several parts of the world, and BP-3 is considered " safe as used" and is an allowed sunscreen agent everywhere. If that was not enough, Wikipedia claims that BP-3 is nowadays the most common allergen found in sunscreens, and the always-trustworthy smartskincare writes that " have been shown in some studies to promote the generation of potentially harmful free radicals". In fact, a 2004 follow-up study to examine the estrogenic effect of sunscreens when used topically on the whole body found that "the endogenous levels of reproductive hormones were unaffected" (even though BP-3 could be detected both in plasma and urine, so its absorption is no doubt too good). Estrogenic activity was confirmed only in-vitro (in test tubes) and when taken orally by lab animals, and not when used topically as you would normally. Pentaerythrityl Tetra-Di-T-Butyl HydroxyhydrocinnamateĪnother concern of BP-3 is that it shows some estrogenic activity, though it's probably not relevant when applied topically to the skin.