Sunscreens are one of the most effective methods to protect the skin from the sun’s harmful rays. Sunscreens also prevent premature aging and skin cancer. There are two types of sunscreens, chemical and physical barriers. Of the two, physical barriers work by reflecting or scattering the UV rays away from the skin. They are not absorbed into the skin.
Until recently, zinc oxide sunscreen formulations appeared as a thick, white paste on the skin. However, new nanotechnology has revolutionized the opaque appearance of zinc oxide by refining the zinc particles to make them smaller. But can these tiny particles be harmful to our body?
When shopping for a sunscreen, it is not only important to know what ingredients are safe and effective in combating the sun’s harmful rays, but it is also important to understand what terms like “micronized,” “nanosized,” and “nanoparticles” refer to when it comes to your sunscreen.
Sunscreen Particle Size Matters
Zinc oxide is a common ingredient found in many sunscreens that are effective in blocking ultraviolet A (UVA) rays.[1,2] While it is an effective physical sun blocker, it does have some cosmetic drawbacks. Zinc oxide is classically associated with the pasty white lifeguard nose. It’s thick white appearance is what makes it so effective, but also not a popular choice when selecting between different sunscreens.
The efficacy and cosmetic nuisance are due to the size of the zinc particle. To reduce the opaque appearance of zinc oxide, many sunscreen companies are making the particle smaller through a process referred to as “micronizing” to produce nanosized zinc particles. Nanoparticles are particles are typically less than 100 nanometers in diameter or 0.1 microns. For comparison, 10,000 nanoparticles could fit in the diameter of a human hair!
As the size of these particles decreases, the surface area covered on the skin increases, as well as the reduction of the opaque appearance without compromising the UV coverage. Additionally, the smaller sized particle converts from solely blocking UVA rays to becoming a broad-spectrum sunscreen, with an increased ability to block UVB rays.[1,2]
Are Sunscreens with Nanoparticles Safe?
The concern with nanoparticles is that they can be absorbed by the skin and harm living tissues within the body. However, several studies including both in-vitro (studies on isolated skin cells, or pieces of skin tissue) and in-vivo (studies using live humans and other animals) suggest that systemic absorption is unlikely. Studies using both animal and human skin have shown that nanoparticles do not penetrate the underlying layers of skin, with penetration limited to the outermost layer of the skin, the stratum corneum.[3-5]
So, yes! Sunscreens containing micronized zinc particles are safe to apply to the skin, with the added cosmetic benefit of a more natural appearing application.
What About My Lungs?
Some studies suggest that if nanosized particles were to be ingested or inhaled, they can potentially cause harm to the lungs. This is because these tiny particles can activate an innate immune reaction, which would lead to the production of reactive oxygen species (ROS). ROS create free radicals that can cause harm to cells inside the body. However, conflicting studies done in rodents demonstrate that immune cells (macrophages) can effectively recognize and destroy nanosized particles when inhaled.
While more research still needs to be done, perhaps it would be advantageous to avoid spray-on sunscreens, loose powdered makeup containing nanoparticles, as well as sun protectant chap stick containing nanoparticles in order to prevent accidental inhalation and ingestion. At the very least, breathe out while applying sunscreens around your nose.
Do Nanoparticle Sunscreens Work Differently?
It turns out that nanoparticles do work differently from non-nanoparticles. Zinc is a good example. One of the reasons that nanoparticles are more clear and sheer is that they reflect less and less of visible light as the particle size becomes smaller and smaller. What this means is that nanoparticle zinc may not be as good as blocking blue light. Blue light may have an important role in oxidative stress to the skin and in stimulating melasma more than ultraviolet radiation type A (UVA) so you may need to take this into account if these are problems for you.
Table 1. Nanoparticles vs non-nano zinc
Type of Sunscreen
Broader coverage against UVB, UVA, and blue light
More white and visible
Broad coverage and less visible on the skin
The coverage is not as broad and may no cover very long wavelength UVA and blue light
What Brands Have Nanosized Zinc?
Recall that zinc oxide is the ingredient in sunscreen that is responsible for making the skin pasty and white after application. For this reason, manufacturers make the zinc oxide particles smaller to minimize the whiteness of the skin after application. This is certainly more appealing than having a chalky white face, right? Companies may enticingly label sunscreen products as “invisible zinc”, “sheer” or “clear”. These words give clues that these products most likely contain nanosized zinc particles.
How Can You Tell Whether a Sunscreen Has Nanoparticles or Not?
The Food and Drug Administration (FDA) does not currently have rules against varying sizes or types of zinc oxide particles in sunscreens (FDA11a). Therefore, reading the back of the label to find out what is in your sunscreen might not always be your best option, although some companies are starting to label the type of zinc oxide contained within their product. Even though not all sunscreen labels will reveal what type of zinc is within them, it is still important to always read to the back of sunscreen labels to ensure there is zinc, as well as determine the type of coverage the sunscreen has.
If a sunscreen does not contain nanosized zinc, some companies label “non-nano” next to the ingredient. For example, a label might read “Zinc Oxide 20% (non-nano).”
Table 2. Brands containing non-nanosized and nanosized zinc particles
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