ensulizole

Also known as phenylbenzimidazole sulfonic acid, ensulizole is a water soluble sunscreen ingredient that works in the UVB range, offering no UVA protection. For this reason, ensulizole should always be paired with one or more UVA-screening sunscreen actives in any SPF-rated product labeled “broad spectrum”.

There’s some controversy in the research about what some refer to as ensulizole potentially being a “double-edged sword” for skin. Studies on fish scales and bat skin have shown it protects against oxidizing molecules generated by UVB exposure but it can also trigger DNA damage within skin. Although this hasn’t shown to be true on human skin, it may at least partially explain why ensulizole is not commonly found in sunscreens, despite having very few reports of triggering allergic reactions on human skin.

Aesthetically, ensulizole feels lighter and less oily than most synthetic sunscreen actives, so is sometimes chosen when the goal is a very lightweight texture, although the mineral actives titanium dioxide and zinc oxide can also feel surprisingly light on skin.

Ensulizole concentrations up to 4% are approved for use in sunscreens sold in the United States, Australia, New Zealand, and Korea. In most other parts of the world, ensulizole concentrations up to 8% are permitted, with the exception of Japan, whose maximum permitted amount is 3%.

Along with protecting skin from UVB damage, ensulizole or its salts are sometimes included in cosmetics whose clear packaging would otherwise allow the formula inside to discolor due to ongoing light exposure. Salt forms of ensulizole include potassium phenylbenzimidazole sulfonate, sodium phenylbenzimidazole sulfonate and TEA-phenylbenzimidazole sulfonate.

This sunscreen active is one of several currently undergoing further safety testing under the purview of the United States Food and Drug Administration (FDA). This testing is to gain a better understanding of the systemic absorption, metabolism, and elimination of these sunscreen actives when small amounts enter the body via topical use. It’s important to know that the presence of this or other sunscreen actives in the body does not mean your health is at risk. It is anticipated that the additional testing being done will reaffirm the safety of these ingredients; however, those who remain concerned can choose sunscreens with mineral actives (titanium dioxide and zinc oxide) which are not included in the FDA’s new call for additional testing.

References for this information

Contact Dermatitis, August 2019, pages 151-152
Journal of Investigative Dermatology, October 2010, pages 2,463–2,471
Shaath, Nadim A., The Encyclopedia of Ultraviolet Filters, Allured Publishing, 2007, pages 162–163
https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=352.10&SearchTerm=phenylbenzimidazole%20sulfonic%20acid%20
Photochemistry & Photobiology, February 2002, pages 107–116

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