The Role of Titanium Dioxide in Cosmetic Chemistry
Titanium, a metal and element, gets its name from the Titans, the deities in Greek mythology who preceded the Olympians. Titanium was discovered by William Gregor in 1791 in Cornwall, Great Britain and was given its name by German chemist Martin Klaproth who discovered it independently and nearly simultaneously.
From the chemical point of view, titanium has several oxidation states and combines with oxygen to form titanium monoxide, titanium dioxide and di-titanium trioxide. Titanium dioxide is a white, water insoluble solid that occurs in nature as rutile, a mineral with very interesting optical properties, such as a very high refractive index. Titanium dioxide can be ground to micronized powders consisting of quasi-spherical particles having a “diameter†of about one micrometer. These powders absorb ultraviolet radiation and their extinction coefficient is very high and practically constant across the UV range. This makes titanium dioxide (TiO2) a great UV filter and a material of choice for sunscreens.
TIO2 in Sunscreens
In the US, UV filters are considered drugs. The US Food and Drug Administration (FDA) issues guidelines to indicate that sunscreens are OTC drugs and that they must be prepared according to a specific legislation. For the FDA, acceptable UV filters must be Generally Recognized As Safe and Effective (GRASE) and are classified in a positive list, with the indication of the maximum concentrations allowed. In recent years the FDA has declared that to be considered GRASE, many UV filters need further proof of safety. The FDA proposes a not-GRASE status for sunscreens containing para-aminobenzoic acid (PABA) and trolamine salicylate, because of documented safety issues. In addition, the FDA proposes a not-GRASE status for cinoxate, dioxybenzone, ensulizole, homosalate, meradimate, octinoxate, octisalate, octocrylene, padimate O, sulisobenzone, oxybenzone and avobenzone, because it insists that additional data is needed to show that these UV filters are GRASE.
