Are Sunscreens with Nanoparticles of Zinc Oxide Safe?
Products using nanotechology and materials has become more and more common. Zinc oxide (ZnO) and titanium dioxide (TiO2) are used in nanoparticle size in sunscreens. They provide physical blocks from the harmful UVA and UVB rays, protecting the skin from photo-damage which is known to cause skin cancers.
One nanometer (nm) is roughly 100,000 times smaller than a human hair. The physical and chemical properties of nanoscale materials, such as reactivity, persistence, or bioavailability, can differ significantly from their larger scale counterparts. This is the concern of the group Friends of the Earth who feel that sunscreens with nanoparticles are a risk to your health and urge you not to use them.
Zinc oxide and titanium dioxide nanoparticles used in sunscreens range in the 20 – 30 nm size. Their use in sunscreen has become popular as the nanoparticles appear transparent when applied to the skin rather than an opaque white cover. This transparency makes the sunscreen much more cosmetically acceptable than the larger-particle ZnO and TiO2 use.
While the FOTE quote a recent Australian study by Macquarie University's Professor Brian Gulson as evidence that sunscreens using nano-ZnO are potentially hazardous due to absorption into the blood stream through the skin, Gulson in an interview notes that his study doesn't shed any light on the question of whether the nano-particles themselves played a part in the zinc absorption. “That was the most critical thing. This isotope technique cannot tell whether or not it's a zinc oxide nano-particle that got through skin or whether it's just zinc that was dissolved up in contact with the skin and then forms zinc ions or so-called soluble ions. So that's one major deficiency of our study.”
Other studies not mentioned by FOTE suggest the case for safe, non-penetrating, transparent, topical ZnO sunscreen formulations appears to be strengthening as the one by Sheree Cross and colleagues.
Another concern in the use of nanoparticles in sunscreens is the exposure of the body due to oral and nasal uptake due to application to the lips and mouth area, around the nose, and via contact with sunscreened hands and food.
Philip Moos and colleagues looked at the effects of nanomaterials in the colon. Their experiments used cell cultures of colon cells to compare the effects of zinc oxide nanoparticles to zinc oxide sold as a conventional powder. They found that the nanoparticles were twice as toxic to the cells as the larger particles. This is a study of cell cultures which now needs to be looked at again in living gut before getting too concerned. The scientist also not that the concentration of nanoparticles that was toxic to the colon cells was equivalent to eating 2 grams of sunscreen - about 0.1 ounce.
While the final word may not be out on the safety of nanoparticles in sunscreens at this point I feel safe in using them and recommending their use to family, friends, and patients. No sunscreen is recommended for oral consumption, so care should always be used in washing your hands prior to eating.
Lips are an area commonly involved in skin cancer formation, so it is important to protect them. When using sunscreen lip balm, don’t lick your lips. This will reduce the accidental ingestion of any potentially harmful chemicals, nanoparticle or not.
If you continue to be worried about nanoparticles or other chemicals in sunscreens, then use other sun safe practices:
- Staying in the shade, especially between the sun’s peak hours (10 a.m. - 4 p.m.).
- Covering up with clothing, a brimmed hat and UV-blocking sunglasses.
- Avoiding tanning and UV tanning booths.
Friends of the Earth: Nanosunscreens Threaten Your Health
Human Skin Penetration of Sunscreen Nanoparticles: In-vitro Assessment of a Novel Micronized Zinc Oxide Formulation; Sheree E. Cross, Brian Innes, Michael S. Roberts, Takuya Tsuzuki, Terry A. Robertson, Paul McCormick; Skin Pharmacol Physiol 2007;20:148–154; DOI: 10.1159/000098701
ZnO Particulate Matter Requires Cell Contact for Toxicity in Human Colon Cancer Cells; Philip J. Moos, Kevin Chung, David Woessner, Matthew Honeggar, N. Shane Cutler and John M. Veranth; Chem. Res. Toxicol., 2010, 23 (4), pp 733–739; DOI: 10.1021/tx900203v