Ensulizole
A water-soluble UVB filter used in light facial sunscreens.
Banned in
- Palau
Also excluded where only mineral sunscreen is allowed
- Maui County
- Hawaiʻi County
Where it’s restricted
Named in the law or guidance
| Location | Status | Since |
|---|---|---|
| Palau law text ↗ | In force | January 1, 2020 |
Also not allowed under mineral-only rules
Ensulizole isn’t named in these laws, but they allow only mineral (zinc oxide or titanium dioxide) sunscreens, so a product containing it is excluded anyway.
- Maui County (Maui, Molokaʻi, Lānaʻi) (in force since October 1, 2022)
- Hawaiʻi County (Big Island) (in force since December 1, 2022)
Why it’s regulated
In its 2021 proposed order, the FDA did not propose generally recognized as safe and effective (GRASE) status for ensulizole, because it said more data are needed. The FDA says this proposal does not mean ensulizole is unsafe.
What the reef research says
A 2021 review of coral samples reports that neither of two studies found median phenylbenzimidazole sulfonic acid (ensulizole) above detection limits. A 2023 Frontiers paper cites Baltic Sea measurements of 1.0 to 170 ng/L for PBSA. In a 2021 study, ensulizole was more toxic to mussels at 10 µg/L than at 100 µg/L. In a 2022 Scientific Reports study, pure ensulizole strongly reduced photosymbiont activity in the foraminifer Heterostegina depressa at concentrations up to 200 mg/L. A 2023 zebrafish study found that exposure to 20 µg/L caused a slight decrease in the female gonadosomatic index.
Sources (6)
- Coral UV filter review: A Critical Review of Organic Ultraviolet Filter Exposure, Hazard, and Risk to Corals (Environ Toxicol Chem, 2021; PMC8048829)
- Frontiers in Marine Science 2023: Life cycle exposure to 2-phenylbenzimidazole-5-sulfonic acid disrupts reproductive endocrine system and induces transgenerational adverse effects in zebrafish
- Biomarker-based assessment of sublethal toxicity of organic UV filters (ensulizole and octocrylene) in a sentinel marine bivalve Mytilus edulis (Sci Total Environ 2021; PMID 34329935)
- Photosynthetic performance of symbiont-bearing foraminifera Heterostegina depressa affected by sunscreens (Sci Rep 2022; PMID 35177723)
- FDA: Questions and answers on FDA's regulatory actions on OTC sunscreen
- 21 CFR 352.10, Sunscreen active ingredients (eCFR; ensulizole, meradimate, octinoxate and octisalate appear under their revised names in the stayed 2002 amendment)
Related ingredients: Octocrylene, Avobenzone, Octinoxate
Last reviewed October 14, 2026.