Inert earth mineral used as a thickening, whitening, lubricating, and sunscreen ingredient in cosmetics. It protects skin from UVA and UVB radiation and is considered to have no risk of skin sensitivity.  Because of its gentleness, titanium dioxide is an excellent sunscreen active for use on sensitive skin. It’s also great for use around the eyes, as it is highly unlikely to cause stinging.
Titanium dioxide is typically micronized and coated for use in cosmetics products. The micronizing makes this somewhat heavy-feeling ingredient easier to spread on skin, plus a bit more cosmetically elegant. Micronized titanium dioxide also is much more stable and can provide better sun protection than non-micronized titanium dioxide. Micronized titanium dioxide does not penetrate skin so there’s no need to be concerned about it getting into your body. Even when titanium dioxide nanoparticles are used, the molecular size of the substance used to coat the nanoparticles is large enough to prevent them from penetrating beyond the uppermost layers of skin. [2,3] This means you’re getting the sun protection titanium dioxide provides without any risk of it causing harm to skin. The coating process improves application, enhances sun protection, and also prevents the titanium dioxide from interacting with other ingredients in the presence of sunlight, thus enhancing its stability. It not only makes this ingredient much more pleasant to use for sunscreen, but also improves efficacy and eliminates safety concerns. Common examples of ingredients used to coat titanium dioxide are alumina, dimethicone, silica, and trimethoxy capryl silane.
Titanium dioxide as used in sunscreens is commonly modified with other ingredients to ensure efficacy and stability. Examples of what are known as surface modifier ingredients used for titanium dioxide include stearic acid, isostearic acid, polyhydroxystearic acid, and dimethicone/methicone copolymer.
Some websites and doctors maintain that titanium dioxide is inferior to zinc oxide, another mineral sunscreen whose core characteristics are similar to those of titanium dioxide. We’re not sure where the information about titanium dioxide not being a great active sunscreen ingredient came from, but the reality is 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 any sunscreen ingredient is defined as one that surpasses 360 nanometers (abbreviated as “nm,” this is how the sun’s rays are measured). Titanium dioxide exceeds this range of protection, but depending on whose research you look at, it either performs as well as or slightly below zinc oxide.
Although it’s true that titanium dioxide does not rank as high for UVA protection as zinc oxide, it ends up being a small measurement of difference (think about it like being 10 years old versus 10 years and 3 months old). This is not easily understood in terms of other factors affecting how sunscreen actives perform (such as the base formula), so many, including some dermatologists, assume that zinc oxide is superior to titanium dioxide for UVA protection. When carefully formulated, titanium dioxide provides excellent UVA protection. Its UVA protection peak is lower than that of zinc oxide, but both continue to provide protection throughout the UVA range for the same amount of time. 
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- van Hoogdalem E. Transdermal absorption of topical agents in man; review of clinical pharmacokinetic data. J Eur Acad Dermatol Venereol. 1998;11(S1):@13-9.