SUN CARE
107
Zinc oxide: Winning choice for a sunscreen UV filter
Dr Paul Williams, U.S. Zinc
It is well known that sunscreen prevents sunburn, reduces the risk of melanoma and reduces the sun-related ageing of skin. Consumers not only demand that sunscreen be effective, they also prefer sunscreens with organoleptic properties. In addition, there is a growing trend for
sunscreens to contain natural ingredients that can safely be applied to human skin and which are environmentally safe. These are some of the more recent challenges that manufacturers face as they design their sunscreen formulations. The manner and extent of regulation of
sunscreens vary across the world. In the USA, the FDA regulates sunscreens as a drug. In Canada, depending upon its formulation, a sunscreen might be classified either as a natural health product or an over-the-counter drug.1,2 In the EU, Chinese and Japanese sunscreens
are regulated as cosmetics. Australia regulates sunscreen as a cosmetic if its sun protection factor (SPF) is a secondary function and as a therapeutic/drug if SPF is a primary function.1,2 The primary focus of most regulations is a
sunscreen’s UV filter, the component that provides protection from UV rays. UV filters are classified in three wavelengths regions: the longest is UVA1 (340-400 nm), the intermediate is UVA2 (320- 340nm) and the shortest is UVB (290-320 nm). Although it is common not to differentiate
between UVA1 and UVA2, some UVA filters do not have optimal performance in both of these regions. UVA rays have less energy and do not burn the skin like UVB rays, but they have been shown to accelerate skin ageing, as well as having the potential to contribute to melanoma.
Organic & inorganic filters Currently the FDA has approved 16 active UV filter ingredients (Table 1) for sunscreens,3
including two inorganic (or mineral-based) filters - zinc
TABLE 2: FDA CLASSIFICATION OF UV FILTERS Category
Description 1 2 GRASE Non GRASE – not permitted in sunscreen
Zinc oxide Titanium dioxide
Aminobenzoic acid Trolamine salicylate
3 Require further evaluation
Avobenzone Cinoxate Dioxybenzone Ensulizole Homosalate Meradimate
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Octinoxate Octisalate Octocrylene Oxybenzone Padimate O Sulisbenzone
oxide and titanium dioxide - and 14 organic filters. Inorganic filters reflect UV rays’ radiation, while organic filters absorb it. Importantly, inorganic filters do not break down when they reflect radiation, whereas when organic filters absorb radiation, they have the potential to break down into smaller, more hazardous materials. Moreover, it has been demonstrated that the
organic filters readily penetrate the skin. Organic UV filters have been found in the bloodstream for seven days after using the sunscreen.5
In
comparison, one recent study shows that the inorganic minerals from UV filters are not found in the bloodstream after using sunscreen. One of the biggest questions debated about mineral-based UV filters is whether
UV filter
TABEL 1: FDA ACTIVE UV FILTERS FOR USE IN SUNSCREENS Aminobenzoic acid Avobenzone* Cinoxate
Dioxybenzone
Homosalate* Meradimate Octocrylene* Octinoxate*
* Most commonly used UV filters in the US4
micron- or nano-sized mineral particles should be used. Nano-based UV mineral filters are under investigation for potential inhalation if the sunscreen is applied as a spray.5
Octisalate*
Oxybenzone* Padimate O Ensulizole
Sulisobenzone
Titanium dioxide* Trolamine salicylate Zinc oxide*
Therefore, nano-
based mineral UV filters should not be formulated in spray applications.
Safety profiles The safety profile of zinc oxide and titanium dioxide micron and nano-sized materials was found in recent studies to be similar in terms of cytotoxicity, genotoxicity, photo-genotoxicity, general toxicity and carcinogenicity, as well as being non-toxic, independent of particle size. To date, the preponderance of studies show that mineral-based UV filters show negligible to no risk while providing significant protection to human skin from UV rays.6 The only UV filter approved in the USA for use in sunscreens that provides protection in all three wavelength regions is zinc oxide. In the EU, Japan and Australia, two additional organic UV filters (methylene bis-benzotriazolyl tetramethylbutylphenol and diethylhexyl butamido triazone) have been approved for use in sunscreens that provide protection in all three wavelength regions. Currently, these are only approved for use in personal care products and cosmetic applications in the USA and cannot be used as an active UV filter in sunscreens.7 In February 2019, the FDA provided an update on the status of UV filters.8
They were
divided into three categories, as described in Table 2.7
The two mineral UV filters were
placed in Category 1. The FDA stated that those in the require further evaluation class are not necessarily unsafe, but rather need more study prior to being considered Generally Recognised as Safe and Effective (GRASE). The European Commission has recently published preliminary results on the safety of three organic UV filters: oxybenzone, homosalate and octocrylene. All three have been shown to have endocrine-disrupting effects.
April 2022 PERSONAL CARE
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