Freshwater algae show low-to-moderate susceptibility to TiO₂ exposure, with more pronounced toxic effects in the presence of UV irradiation. It has also been shown that nano-sized TiO₂ is significantly more toxic to algae Pseudokirchneriella sub-capitata than submicron-sized TiO₂. Hund-Rinke and Simon  reported that UV irradiated 25 nm TiO₂ NPs are more toxic to green freshwater algae Desmodesmus subspicatus than UV irradiated 50 nm particles, which is in agreement with Hartmann et al. UV irradiated TiO₂ NPs also inactivated other algae species such as Anabaena, Microcystis, Melsoira and Chroococcus. It was demonstrated that smaller particles have a greater potential to penetrate the cell interior than submicron-sized particles and larger aggregates. Studies have shown that the amount of TiO₂ adsorbed on algal cells can be up to 2.3 times their own weight.

Some websites maintain titanium dioxide is inferior to zinc oxide, another mineral sunscreen ingredient whose core characteristics are similar to those of titanium dioxide. The reality is that titanium dioxide is a great broad-spectrum SPF ingredient and is widely used in all manner of sun-protection products. What gets confusing for some consumers is trying to decipher research that ranks sunscreen ingredients by a UV spectrum graph. By most standards, broad-spectrum coverage for sunscreen ingredients is defined as one that surpasses 360 nanometers (abbreviated as “nm” - how the sun’s rays are measured). Titanium dioxide exceeds this range of protection, but depending on whose research you read, it either performs as well as or slightly below zinc oxide.