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Avobenzone in Pool Water: What the Chemistry Shows, and What's Still Unknown
Executive Summary
Avobenzone is Australia's most widely used sunscreen filter. It appears in nearly 70% of Australian sunscreens, 641 of 924 products on the Australian Register of Therapeutic Goods.
Avobenzone changes chemically when it meets pool chlorine. Laboratory work identified more than 60 new compounds formed by the reaction, and samples from two real swimming pools contained several of them.
The part of avobenzone that absorbs UV is the part that reacts. The reaction is a direct consequence of how the filter is built, not a fault in any particular product.
Nobody has measured what a swimmer is actually exposed to. There is no figure for how much reaches a person, no dose at which effects begin, and no health outcome linked to these specific compounds.
Zinc oxide is not part of this chemistry. It is a mineral rather than a carbon-based filter, and it has no equivalent reactive structure. Advance ZincTek manufactures pharmaceutical-grade non-nano zinc oxide in Queensland.
What happens in the water
Avobenzone absorbs UV through a particular arrangement of atoms at the centre of its structure. That same arrangement is chemically reactive toward chlorine, which is why the filter transforms on contact with the disinfectant pools are kept at. (Trebše et al., 2016)
Researchers tested this directly, mixing avobenzone with chlorine and bromine disinfectants in fresh and sea water, both in the dark and under UV light. They used a technique that identifies unknown compounds by their individual chemical fingerprint, and found more than 60 new products across the full set of conditions. They then tested two ordinary swimming pools and found several of the same compounds present at levels they described as high. (Lebedev et al., 2020)
Why the sunscreen itself does not settle it
The same study compared pure avobenzone with avobenzone inside three commercial sunscreens. On its own it reacted immediately. Inside the finished products, around 98 to 99 per cent of it was still intact after an hour, because antioxidants and other ingredients in the formula compete for the chlorine first. (Lebedev et al., 2020)
That sounds reassuring until it is placed against how people actually swim. Sunscreen washes off continuously, a swim lasts hours rather than one hour, and a busy pool has many people contributing at once. The compounds turning up in real pool water are the evidence that a slowed reaction still reaches the same end point. What the formulation buys is time, not immunity, and nobody has measured how that plays out across a full day at a public pool.
Which compounds matter most
Most of the 60-plus products have never been studied on their own. Two of the chemical families involved have been: chlorinated phenols and chlorinated acetophenones are both recognised as irritants to skin, eyes and airways.
Byproducts of avobenzone that are already known irritants can survive attempts to remove them from treated water, with halogenated acetophenones proving the hardest to strip out (Wang et al., 2017). No official regulator has tested what happens to avobenzone once it's in treated water. Both the TGA and FDA assess how much passes through skin, not what forms downstream of that, so this question falls outside either framework (Therapeutic Goods Administration, 2025).
Where zinc oxide sits
The reactions described here happen at a carbon-based structure that zinc oxide does not have. Zinc oxide is a mineral filter, so this transformation chemistry does not apply to it. It is also the only mineral UV filter that independently achieves true broad-spectrum protection, including deep UVA1 wavelengths, without requiring combination with another active ingredient (Beasley and Meyer, 2010).
ZinClear XP, manufactured by Advance ZincTek, is a pharmaceutical-grade, uncoated, non-nano zinc oxide produced under GMP-certified conditions in Queensland, supplied in five BET surface area grades from 15 to 44 square metres per gram.
References
Lebedev AT, Bavcon Kralj M, Polyakova OV, Detenchuk EA, Pokryshkin SA, Trebse P (2020). Identification of avobenzone by-products formed by various disinfectants in different types of swimming pool waters. Environment International 137: 105495. DOI 10.1016/j.envint.2020.105495
Wang C, Bavcon Kralj M, Kosmrlj B, Yao J, Kosenina S, Polyakova OV, Artaev VB, Lebedev AT, Trebse P (2017). Stability and removal of selected avobenzone's chlorination products. Chemosphere 182: 238-244. DOI 10.1016/j.chemosphere.2017.04.125
Trebse P, Polyakova OV, Baranova M, Bavcon Kralj M, Dolenc D, Sarakha M, Kutin A, Lebedev AT (2016). Transformation of avobenzone in conditions of aquatic chlorination and UV-irradiation. Water Research 101: 95-102.
Therapeutic Goods Administration (2025). Safety Review of Seven Active Sunscreen Ingredients.
Beasley DG, Meyer TA (2010). Characterization of the UVA Protection Provided by Avobenzone, Zinc Oxide, and Titanium Dioxide in Broad-Spectrum Sunscreen Products. American Journal of Clinical Dermatology 11(6): 413-421.
Australian Register of Therapeutic Goods, product counts across 924 therapeutic sunscreen products.
