ScienceDaily (Nov. 30, 2011) — Ultra-tiny zinc oxide (ZnO) particles with dimensions less than one-ten-millionth of a meter are among the ingredients list of some commercially available sunscreen products, raising concerns about whether the particles may be absorbed beneath the outer layer of skin. To help answer these safety questions, an international team of scientists from Australia and Switzerland have developed a way to optically test the concentration of ZnO nanoparticles at different skin depths. They found that the nanoparticles did not penetrate beneath the outermost layer of cells when applied to patches of excised skin.
The results, which were published this month in the Optical Society’s (OSA) open-access journalBiomedical Optics Express, lay the groundwork for future studies in live patients.
The high optical absorption of ZnO nanoparticles in the UVA and UVB range, along with their transparency in the visible spectrum when mixed into lotions, makes them appealing candidates for inclusion in sunscreen cosmetics. However, the particles have been shown to be toxic to certain types of cells within the body, making it important to study the nanoparticles’ fate after being applied to the skin. By characterizing the optical properties of ZnO nanoparticles, the Australian and Swiss research team found a way to quantitatively assess how far the nanoparticles might migrate into skin.
The team used a technique called nonlinear optical microscopy, which illuminates the sample with short pulses of laser light and measures a return signal. Initial results show that ZnO nanoparticles from a formulation that had been rubbed into skin patches for 5 minutes, incubated at body temperature for 8 hours, and then washed off, did not penetrate beneath the stratum corneum, or topmost layer of the skin. The new optical characterization should be a useful tool for future non-invasivein vivo studies, the researchers write
I have been following the controversy of nano particles and the latest research shows that nano zinc oxide particles produce free radicals on the skin when in contact with sunlight which seems to defeat the purpose of the sunscreen. Can you comment on this? Thanks
Dear Virginia,
First, we know of any research that shows that using a nano/micronized zinc oxide is any different on the skin from macro zinc oxide. Your question indicates that you have a study relating to some sort of catalytic function at the stratum corneum level. If you can forward this to me, I will have of scientist comment specifically on the research.
The UV spectrum causes free radicals and cellular deformation in the deep tissue of unprotected skin. The current research we have looked at from NIH contradicts what you say because here is no absorption of zinc oxide below the stratum corneum, which is the outer barrier level of dead skin.
Any free radical produced would have to be at the spinosum level. Zinc Oxide coated or uncoated never reaches that level. The article herein has information with photographs shown the ZnO on the surface of the stratum corneum. The basic concept of why ZnO has been used for over 75 years is because it blocks UV as a physical barrier from getting to deep tissue where aging and skin cancer occurs.
ZnO itself is an oxide and does not produce free radical unless it is exposed to strong unnaturally occurring UVA radiation in deep skin tissue. Literally, it is like staying in a tanning bed for 72 hours to get that level of UV. This also assumes no antioxidants naturally existing in the skin or from antioxidants used to build the lotion base of a sunscreen. One must account for the level of UV intensity, the supposition that the ZnO is in contact with deep tissue and that there are no antioxidants present that significantly reduces the validity of the assumption that ZnO produces free radicals. Further, there is no scientific principle that extrapolates that a macro Zno performs differently and one that is smaller in size. The opposite being much more likely.
Since we do not produce a “go to beach” or direct exposure sunscreen, our perspective is quite different from sunscreen makers. To us the best form of UVA and UVB protection is to cover-up with UV protective clothing. From our perspective, lying in the sun without a ZnO based sunscreen will definitely produce free radicals in deep tissue merely by the nature of deep penetrating UV radiation. Also of concern with chemical sunscreens is the conversion of UV to another form of energy. There is some new studies started in Australia trying to map the chemical conversion process, but it is too early to comment. In our opinion based on numerous scientific studies and the length of time it has been in use, ZnO is the best alternative to covering up.
Please do send your research so that we can publish it here and comment further.
Regards,
Mickey
You note in response to Virginia’s post: “The UV spectrum causes free radicals and cellular deformation in the deep tissue of unprotected skin. The current research we have looked at from NIH contradicts what you say because here is no absorption of zinc oxide below the stratum corneum, which is the outer barrier level of dead skin.”
Dead skin is sloughed off by wash clothes at the very basic level, and buffers/scrubs at the higher level. Either removes the dead skin “barrier” leaving it open for absorption of nano particles. Would you agree?
Why not just use NON-NANO ZINC in your Luminous Moisturizer SPF 30? I like the product but would feel safer about non-nano zinc.
Thanks for your consideration.
Hi Becky,
First, there are over 400 studies that show that nano-ZnO is safe and none that show a safety issue. Even the EWG supports the efficacy of Nano-ZnO. Our own research shows the increased efficacy of Nano-ZnO because of the increased compaction and therefore increased coverage. I think you comment incorrectly assumes that Nano-ZnO is unsafe.
Part of the prerequisite of our customer tests is that they want their sunscreen to not make their skin look blue of white. If you read the new 2013 EWG Sunscreen report, you will see their comment that most, if not all, sunscreens claiming non-nano are indeed nano. Simply, we have never found a non-nano ZnO particle that does not leave a white or blue cast on the skin. We are as bold to say that if you apply a sunscreen and it is not white or blue on the skin, it is nano. We have written a couple of articles herein and have tested some of the most popular brands.
I hope this answers you question.
Regards,
Mickey
Hi Becky,
We use a combination zinco oxide th is mos spherical nano particles because it has higher efficacy and it will not whiten the skin. Simply, if a particle is micron size or above, it creates a white cast. If you read the comments in the new EWG Sunscreen Report, you will see their belief that the majority of companies claiming non-no are in fact nano.
As far as the penetration issue, you took the quote out of context. Many of the penetration studies, now nearly 500 peer reviewed, tested on lung tissue which has the highest permeability. To my knowledge, there are no actual studies, only opinion, that show any penetration of ZnO of any size particle. This is not the case with the chemical versions.
I have written a number of article on http://www.CleanGreenCafe.com on the subject including exposing measurement practices by some companies claiming non-nano.
I am a scientist and engineer who is swayed by facts and not unfounded opinion.
Thanks for your comments and I hope I have answered them to at least understand my reasoning.
Regards,
Bob