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Understanding Sunscreen: Micronization And Nanoparticles

May 17, 2011
From the WebMD Archives

When choosing the safest sunscreen, it’s not only important to know which offer the best protection without relying on toxic ingredients, it is also important to understand what terms like “micronization,” “nanosized,” and “nanoparticles” refer to.

Most of us are familiar with the white noses of lifeguards, and parents using non-toxic sunscreens are used to the ghostly pale residue left behind after a good slathering. This whitening is caused by zinc oxide and titanium dioxide, which create a powerful physical barrier to the sun’s rays, but it is cosmetically unacceptable to many people. Historically, in order to sidestep this undesirable result, chemical absorbers were developed to replace these ingredients.

Chemical absorbers are compounds that penetrate the skin and then absorb UV irradiation. These compounds (like PABA, oxybenzone, and benzophenones) have been used for many years primarily because they do not create a whitening effect. But, many chemical filters degrade after prolonged sun exposure, can irritate sensitive skin, and cause other long-term environmental and health impacts.

Coming full circle, manufacturers have been back at the drawing board trying to create a product that uses physical instead of chemical barriers, but doesn’t clog pores and leave a white residue. What they have found is that by shrinking the zinc oxide or titanium dioxide through a process called “micronization,” they can achieve these goals.

Micronization is the process of reducing the average diameter of a solid material’s particles. Usually, the term micronization is used when the particles that are produced are only a few micrometers in diameter. But, the word is used ambiguously and a particle can actually be micronized until it becomes nano-sized.

Nano-sized means having a size measured in nanometers and a nano-sized material is not necessarily a nanoparticle. According to Kim Walls, MS, of Episencial, “a nanoparticle is any particle less than 100 nanometers in diameter. So, a material that has been reduced to 500 nanometers is NOT a nanoparticle because it is 5 times larger than 100 nanometers. (As a point of reference, a particle must be less than 50 nanometers to enter skin cells; less than 70 nanometers to enter the lungs.)”

This brings us to the question of safety. While the larger sized micronized particles appear to be both safe and effective, some questions still linger about the safety of nanoparticles. Preliminary studies seem reassuring for topical use, but there is still concern regarding inhalation or ingestion.

What should you do?
If you use a sunscreen that contains nanoparticles, use a lotion formulation not spray (we don’t recommend spray of any kind) and monitor children to keep hands out of mouths.

If you’re researching different kinds of sunscreens that use micronized particles, you might need to call manufacturers to ask about their ingredients. In particular, ask them specifically if they are using nanoparticles. If you want to leave nothing to chance: ask for the particle size.

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