The sun gives us many things: light, warmth, energy, vitamin D—and ultraviolet rays that can cause skin cancer.
That’s probably why you’ll be thinking about applying lots of sunscreen when you’re at the beach this summer. And sunscreens are getting better at protecting your skin, partly because many now use zinc oxide and titanium dioxide nanoparticles to better reflect the sun’s harmful rays.
But some scientists have raised concerns that sunscreens using these and other nanoparticles might pose health risks to people who use them. Others have argued that these concerns are unfounded.
So, what does the scientific research say?
First, how are nanoparticles different?
Nanoparticles are materials that are about one-billionth of a meter in size (a nanometer). Nanomaterials are typically understood as materials that range in size from 1 to 100 nanometers.
Nanoparticles are so small that they often have different physical, chemical, mechanical, and optical properties than the same material on a macroscale. It’s these different properties that have generated so much excitement around engineering nanoparticles for everything from targeted drug delivery to wrinkle-free shirts to cosmetics, including sunscreen.
Zinc oxide (ZnO) and titanium dioxide (TiO2) are two common sunscreen ingredients. In the past few years, ZnO and TiO2 nanoparticles have been incorporated because they’re transparent, less greasy, and less odorous than non-nano ZnO and TiO2. They’re also reportedly more stable and less irritating.
Are some nanoparticles dangerous to humans?
Whether nanoparticles are dangerous to humans is a complicated question, subject to several qualifications. For one, toxicity may depend on the type of nanoparticle in question: some may exhibit greater toxicity for humans than others, and some none at all. Toxicity may also depend on how humans are exposed to the nanoparticles in question, whether it be through inhalation, oral ingestion, dermal contact, or injection.
For example, so-called carbon nanotubes and carbon nanofibers embedded into final products may pose little risk to consumers because they’re not pure powders. But some evidence suggests that, in an occupational setting where such products are being manufactured, inhaling pure powder carbon nanotubes not yet embedded in the product could lead to health complications similar to those caused by asbestos.
Furthermore, there are concerns that nanoparticles can translocate across the human body. This basically means that once a nanoparticle enters the human body, it could be small enough to move into other parts of the body and cause damage.
What about zinc oxide and titanium dioxide nanoparticles?
What about zinc oxide and titanium dioxide nanoparticles in sunscreen—do they pose risks to human health?
The primary potential pathway through which the nanoparticles could enter the body is, not surprisingly, the skin. But do they actually penetrate the skin? And if they do, are they toxic to humans?
According to a 2016 literature review commissioned by the Australian government on the safety of ZnO and TiO2 nanoparticles in sunscreens, most studies have concluded the following:
- There is some evidence that these nanoparticles might penetrate human skin, but only at a level restricted to the outer layers (though some studies have reportedly found conflicting evidence).
- This penetration does not reach “viable skin cells” that could be damaged by any nanoparticle toxicity.
- The nanoparticles do not achieve “significant concentrations” in humans beyond the outer skin layer.
The review also examined whether exposure to ultraviolet rays could cause the nanoparticles to react in potentially harmful ways, such as through oxidation. The review found that this risk is significantly mitigated by the fact that manufacturers often proactively prevent oxidation by coating the nanoparticles with antioxidant compounds.
The consumer advocacy organization Environmental Working Group (EWG) also notes that, even if the particles do oxidize, human skin’s antioxidant protections would suppress any oxidized nanoparticle toxicity.
In short, there’s little evidence that ZnO and TiO2 sunscreen nanoparticles can penetrate the human body deeper than the skin layers, nor is there much evidence that these nanoparticles harmfully oxidize when exposed to the sun’s rays.
An article in Australian Family Physician argues that the evidence that conflicts with the Literature Review’s findings related to skin penetration warrants further research; however, the publication concluded that “the benefits of sunscreens in terms of reducing skin cancer risk far outweigh the potential risks of long-term use.”
As a recent Health-EU article expressed it, “The only concern to have about sunscreen is…did you remember to put it on?”
Spray sunscreens have raised some concerns related to inhaling nanoparticles: the EWG cautions against using spray sunscreens that contain ZnO or TiO2 particles “of any size” in light of the concerns related to inhaling nanoparticles.
It also notes that nanoparticles could be ingested when applied in lip sunscreens, though there doesn’t appear to be any evidence that this ingestion occurs in volumes high enough to warrant special concern.
What is the impact on insurance exposure?
Current research has found that the risk of potential harm from nanoparticles in the sunscreen you’re using this summer is probably very low, which is good news for sunbathers who want to avoid potential health effects and for sunscreen lotion manufacturers seeking to mitigate potential bodily injury claims and product recalls.
But the potential long-term and latent health impacts of nanoparticles—whether in their pure form or infused into products such as sunscreen—continue to be an area of intense scientific study. ISO Emerging Issues closely monitors developments related to nanotechnology risks.