Zinc Oxide: The Safe Sunscreen Ingredient
Badger's response to Missouri S&T’s Zinc Oxide Press Release.
Numerous studies, as well as consumer protection groups such as the Environmental Working Group, have promoted mineral sunscreens as the safest sunscreen option. Yet a recent press release distributed by Missouri University of Science and Technology on May 7, entitled Sunscreen ingredient may pose skin cancer risk, references a not-yet-published study of lung tissue exposed to zinc oxide under UV radiation, and makes a leap from preliminary research to the threat of skin cancer. The study showed an increase in free radical damage to the living lung tissue, but did not explore zinc oxide’s effect on the outermost layer of dead skin cells where sunscreen is applied.
Here at Badger, we take the safety of our sunscreen very seriously, so we’re constantly reviewing emerging research regarding the subjects of zinc oxide, nano particles, and potential free-radical damage. No single sunscreen active ingredient has a better track record for safety, including titanium dioxide. The strong overall safety record of zinc oxide is why Badger has chosen and stands by non-nano zinc oxide as the active ingredient for our sunscreens.
The press release, which can be viewed here, suggests that when exposed to sunlight, zinc oxide undergoes a chemical reaction that may release unstable molecules known as free radicals. After reading the press release, it is clear to us that it’s not Dr. Ma’s intention to suggest that zinc oxide, as used in sunscreen creams, is a carcinogen. Dr. Ma even states within the press release that "more extensive study is still needed; this is just the first step," and that "[he] still would advise people to wear sunscreen." What Ma does not say is that zinc oxide in a sunscreen cream causes cancer.
It’s important to note that his study (in its entirety) has not been released yet. However, based on the summary findings illustrated in the press release, we have four separate points to offer in response.
Point One: The study bears little (to no) relevancy to zinc oxide as applied in sunscreen cream to the surface of the skin, having only demonstrated that zinc oxide “may” have damaging effects on living lung tissue.
Zinc oxide in sunscreen creams sits on top of the outermost layer of dead skin cells (stratum corneum) where it reflects and absorbs damaging UV rays, before UV rays can penetrate and damage living skin cells through free radical activity. Secondary research concludes that micronized and non-nano zinc oxide in sunscreen creams is not absorbed into living skin tissue1,2,3,4. The leap from possible free radical damage in living lung tissue to “sunscreen ingredient that may cause cancer” is not supported by this research. Furthermore, UV rays will penetrate to living cell tissue without sun protection measures, and are known to cause free radical damage5.
Point Two: This research was conducted using nano-particle zinc oxide. The particle range was not disclosed in the initial press release, but based on the language used we can surmise that only nano-particle (100nm and smaller) zinc oxide was used for the research. Badger’s zinc oxide averages over 6,000nm.
Nano-particle zinc oxide has a far greater surface area than non-nano zinc oxide and is thus more reactive6. As sunscreen manufacturers, we have followed the nano particle research very closely, and due to concerns (and the larger unknowns) we made a decision in 2011 to switch from our micronized zinc oxide to larger particle, “non-nano” zinc oxide. Nano-particle zinc oxide is defined as particles below 100nm. The average particle size in Badger sunscreen is 6,000nm (including some agglomeration), well above the nano particle range. Bottom line: this is like comparing apples to bananas, as different sized particles have different reactivity.
Point Three: Antioxidants neutralize free radicals, and Badger’s sunscreen is packed with highly antioxidant ingredients.
A past study conducted by the same authors demonstrated that when living cells exposed to free radical activity come in contact with known antioxidants, the antioxidants neutralize much of the free radical activity7. This is how it works: free radicals are unstable because they are lacking an electron. Antioxidants come along and actually donate one of their electrons, which stabilize the free radical. Badger sunscreens are packed with antioxidants of a much smaller molecular size than zinc oxide, which are absorbed into the skin to the living cell tissue where they are able to neutralize free radical activity that may occur there. Bottom line: zinc oxide sits on a layer of dead skin in a base of antioxidant-rich plant oils, butters, and extracts – antioxidants go in, zinc oxide stays out. These antioxidants neutralize free radical activity wherever they are.
Point Four: Overall safety record versus preliminary research.
Zinc oxide is highly regarded as a safe sunscreen ingredient by the scientific community, and is still recommended as the safest and most effective sunscreen active by prominent medical professionals and consumer advocacy groups8, 9. No single sunscreen active ingredient has a better track record for safety, including titanium dioxide. This strong safety record is why we’ve chosen and stand by zinc oxide as the active ingredient for our sunscreens.
Most notably, Ma's research on zinc oxide's effect on cells is, by his own admission, still in the early stages. He cautions people from drawing conclusions about the safety or dangers of sunscreen based on this preliminary research, and recommends that people continue to use sunscreen since the danger of excessive UV exposure outweighs any conclusions drawn from this study.
We respect Dr. Ma and his research, and anxiously await the release of his full study.
References:About Sunscreen Safety & Necessity in General
1 The in vitro absorption of microfine zinc oxide and titanium dioxide through porcine skin A.O. Gamer, E. Leibold, B. van Ravenzwaay Toxicology in Vitro Volume 20, Issue 3 April 2006, Pages 301–307
2 The safety of nanosized particles in titanium dioxide– and zinc oxide–based sunscreens Marissa D. Newman, MD, Mira Stotland, MD, Jeffrey I. Ellis, MD Journal of the American Academy of Dermatology Volume 61, Issue 4 October 2009, Pages 685–692
3 Safety Evaluation of Sunscreen Formulations Containing Titanium Dioxide and Zinc Oxide Nanoparticles in UVB Sunburned Skin: An In Vitro and In Vivo Study N. A. Monteiro-Riviere, K. Wiench, R. Landsiedel, S. Schulte, A. O. Inman and J. E. Riviere Toxicol. Sci. (2011) 123 (1): 264-280. doi: 10.1093/toxsci/kfr148 First published online: June 3, 2011
4 Stratum Corneum Is an Effective Barrier to TiO2 and ZnO Nanoparticle Percutaneous Absorption P. Filipe, J.N. Silva, R. Silva, J.L. Cirne de Castro, M. Marques Gomes, L.C. Alves, R. Santus, T. Pinheiro Skin Pharmacol Physiol 2009;22:266-275 (DOI: 10.1159/000235554)
5 UV-generated free radicals (FR) in skin: Their prevention by sunscreens and their induction by self-tanning agents K. Junga, M. Seiferta, Th. Herrlingb, J. Fuchsc Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy Volume 69, Issue 5, May 2008, Pages 1423–1428
6 Synthesis, Isolation, and Chemical Reactivity Studies of Nanocrystalline Zinc Oxide Corrie L. Carnes and Kenneth J. Klabunde Department of Chemistry, Kansas State University, Manhattan, Kansas 66506 Langmuir, 2000, 16 (8), pp 3764–3772 DOI: 10.1021/la991498p Publication Date (Web): March 11, 2000
7 Toxicity of nano- and micro-sized ZnO particles in human lung epithelial cells Weisheng Lin, Yi Xu, Chuan-Chin Huang, Yinfa Ma, Katie B. Shannon, Da-Ren Chen and Yue-Wern Huang Journal of Nanoparticle Research Volume 11, Number 1 (2009), 25-39, DOI: 10.1007/s11051-008-9419-7