Titanium dioxide is a common ingredient in sunscreens, and particularly where substitutes for oxybenzone and other endocrine disrupting chemicals are sought, it is the go-to “non-toxic” sunscreen active for its ability to boost SPF ratings. But, The American Cancer Society set the stage for further narrowing the range of safe sunscreen choices. Their report says: “Identification of research needs to resolve the carcinogenicity of high-priority IARC carcinogens”, and goes on to list titanium dioxide as one of their top 5 "suspected carcinogens".
1) Trouiller study
In vivo studies are finally emerging which indicate risks associated with titanium dioxide. One study coming out of UCLA’s School of Public Health involving lab mice almost certainly contributed to the American Cancer Society headline-making decision to list titanium dioxide among the top five potential carcinogens warranting more study. The UCLA study, conducted by molecular biologist Bénédicte Trouiller for almost two years, was simplicity itself; she doused the drinking water of lab mice with titanium dioxide.
About halfway through the initial test the results were so alarming—extensive damage to or outright destruction of DNA and chromosomes—she felt compelled to repeat the tests again and again. While it may seem like a large leap from doctored drinking water ingested by mice to exposure risks to humans it really isn’t, especially given the prevalence of titanium dioxide. Not only is TiO2 one of the top 50 chemicals produced world-wide, the “Environmental Working Group has calculated that close to 10,000 over-the-counter products use it in one form or another.”
2) University of Plymouth study
A recent in vivo study reinforces the concern and the need for more studies. As reported in "Nanoparticles Cause Brain Injury in Fish" (ScienceDaily Sept. 19, 2011): "[Researchers] subjected rainbow trout to titanium oxide nanoparticles which are widely used as a whitening agent in many products including paints, some personal care products, and with applications being considered for the food industry. They found that the particles caused vacuoles (holes) to form in parts of the brain and for nerve cells in the brain to die. Although some effects of nanoparticles have been shown previously in cell cultures and other in vitro systems this is the first time it has been confirmed in a live vertebrate."
3) Gulson study
The argument that it does not penetrate the skin doesn’t just evade the safety question, it implies that it might be a problem if it is absorbed. If the question then becomes, is it absorbed? we can probably extrapolate from emerging studies on zinc oxide to predict that some particles of titanium dioxide would follow the same path, that is, some of them would breach the epidermal barrier and be absorbed.
In a study headed by geochemist Brian Gulson, of Sydney's Macquarie University, before and after blood and urine samples showed that “small amounts” of zinc were absorbed after a 20% zinc oxide sunscreen was applied. Nevertheless, the presence of zinc in the system is not "alarming," as zinc is utilized by the human body. Tracing the pathway of zinc oxide is certainly easier than tracking titanium dioxide, since ZnO ionizes and shows up in elevated zinc levels in blood and urine.
Titanium dioxide behaves differently, however, and we do not yet have the studies to show us how titanium dioxide breaks down once absorbed by the body, where it goes or what it does. Yet if we allowed ourselves to make two fairly reasonable assumptions from the studies cited above they would be:
1) TiO2 can be absorbed (Gulson study), and
2) TiO2 is dangerous (Trouiller and University of Plymouth studies).
Until we know more about titanium dioxide I recommend invoking our old stand-by, the precautionary principle. I realize it narrows your search for a safe sunscreen even more, but I would add titanium dioxide to the list of sunscreen no-no's, along with chemicals and nanoparticles. The safest course of action is non-nano zinc oxide sunscreens.
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