Controlling Hydroxyl Radical Formulation in TiO₂ Sunscreens

By: Nai-Fang Chang and Chang-Chin Kwan, Providence University

Posted: January 29, 2010, from the February 2010 issue of Cosmetics & Toiletries.

The use of titanium dioxide (TiO₂) in cosmetics is extensive; in addition to makeup such as pressed powder cakes, liquid foundations, lipsticks and eye makeup, it is used in sunscreen creams. However, its rutile form for cosmetics may produce small amounts of hydroxyl radicals upon exposure to sunlight. Therefore, in the present article, the authors use salicylic acid (SA) as a hydroxyl radical capture agent to examine the development of free radicals in solutions or creams containing TiO₂ to further examine its safety upon UV exposure.

Characterizing TiO₂
TiO₂ is a nontoxic, fine white powder consisting of uniform particles that has good dispersion and narrow particle size distribution. Its coloration and covering power are higher than zinc oxide or lead carbonate, and for particle sizes in the range of 0.2–0.5 μm, TiO₂ has the largest reflective index (n = 2.7) among all white pigments. It also shows stable chemical properties such as being: insoluble in water and weak acids, slightly soluble in alkaline solutions, and soluble in hot sulfuric and hydrochloric acid. Crystal forms of TiO₂ include anatase, rutile and brookite.

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