The term 'micronized' and 'nanoparticles' have the same meaning. Nanoparticles are not defined by weight or molecular weight but only by size. A common definition is: "A nanoparticle has one or more dimensions of the order of 100nm or less." A large number of clinical studies suggest that micronized zinc oxide (nano-particles) do not penetrate human skin beyond the superficial layers of the stratum corneum and do not pose a health risk (see:
Since nanoparticles can no longer be inhaled once they are incorporated into a cream or lotion inhalation per se is not considered a hazard for the consumer. It seems plausible that nanoparticles that have been incorporated into a spray may pose a health risk as sprays can be inhaled when applied. So far, however, it is not clear what the health hazards really are and what degree of spray inhalation is necessary to create a health problem. Workers who work with micronized particles are advised to carry protective masks or dust respirator.
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