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Water Resistance: What the Claim Means and How It Must Be Proven

Writer: Australian Sunscreen Council
Australian Sunscreen Council
11 minutes ago
6 min read

Australia allows water-resistance claims of up to four hours, but the standardised immersion test does not reproduce every stress of real swimming or sport. Dr Leslie Laquieze explains what the claim means, how it must be proven and why reapplication advice still applies.


By Dr Leslie Laquieze, PharmD, MSc, PhD, MBA, Expert Member, Australian Sunscreen Council


For a country where so much sun exposure happens at the beach, in the pool and on the sports field, water resistance is one of the most consequential claims a sunscreen can make. It is also one that cannot be inferred from a static SPF result.


What Australia requires

The Therapeutic Goods Administration’s Australian Regulatory Guidelines for Sunscreens define water resistant as “a sunscreen product which has been shown after designated periods of water immersion, using in vivo Sun Protection Factor test methods to provide protection against certain of the sun’s UV rays.”

Two Australian features are especially important. According to the TGA’s 2024 paper on the proposed adoption of AS/NZS 2604:2021, “the water immersion procedure for the determination of water resistance now follows ISO 16217:2020,” and “Australia and New Zealand still retain the 4 h water resistance test period and claim and, continue to determine SPF after immersion as the SPF value to use for labelling SPFs.” In other words, an Australian water-resistant SPF 50+ product must achieve the SPF 50+ threshold after the claimed immersion period, not merely before it.


How the test is actually done

The water-immersion procedure is far gentler than real use. ISO 16217:2020 defines the “simulated swim test device” as a “spa, whirlpool or similar device designed for water immersion.” Water is held at 30 ± 2 °C, and each cycle consists of “20 min of immersion of the test subjects with water circulated for the full period” followed by “5 min to 20 min drying time with no towelling permitted between immersion periods.” The standard requires that “the subjects shall sit in a position such that water jets cannot impinge directly on the test sites.”

In other words, the controlled immersion procedure does not reproduce swimming, exercise, sweating, towelling, rubbing against sand or repeated movement through the surf. The rating remains a standardised and useful claim, but it should not be treated as a substitute for directions to reapply after swimming, sweating or towelling and for public-health advice to reapply at least every two hours.


Reapplication and the 80-minute claim

Water resistance does not change reapplication advice. The Australian Standard requires labels to direct users to “apply generously to the skin 20 minutes before skin exposure, then reapply frequently, and after swimming, sweating or towelling” or words to that effect. As Accord Australasia notes in its March 2026 paper Solving Sunscreen: From theory to practice, advertising, including the label, must not be inconsistent with public health campaigns, and “a consistent public health messaging is that all sunscreens should be reapplied frequently, and at least every two hours.” Public-health guidance therefore remains at least every two hours regardless of a longer water-resistance claim. The TGA’s consumer guidance, How to use sunscreens, likewise states: “It’s important to apply and reapply frequently especially when sweating or swimming.”

The United States is more restrictive on duration. Under 21 CFR 201.327, the US Food and Drug Administration permits only two water-resistance statements: “Water Resistant (40 minutes)” and “Water Resistant (80 minutes).” In the author’s experience, this is why many sunscreens sold in Australia by brands that also sell in the United States carry a maximum water-resistance claim of 80 minutes, even though Australia allows claims of up to four hours.


The relevant methods

·         ISO 16217:2020 specifies, in the words of the Swedish Institute for Standards listing, “a procedure of water immersion for the in vivo determination of the water resistance of sunscreen products.”

·         ISO 18861:2020, according to the ISO abstract, “specifies a procedure for evaluating the water resistance retention percentage, by comparing the sun protection factor (SPF) before water immersion (hereafter referred to as the ‘static’ SPF) and after a fixed period of water immersion (hereafter referred to as the ‘wet’ SPF).” It should be applied only according to its exact invocation; the TGA’s guidelines name ISO 16217, ISO 24443 and ISO 24444 as the methods referenced by the Australian Standard.


Best practice for a water-resistance claim

·         Follow the category, duration and labelling required by AS/NZS 2604.

·         Predefine application dose, drying time, immersion, water temperature, agitation, number of cycles, rest periods, calculations and validity rules.

·         For sport, beach or children’s positioning, add robustness modules for sweat, heat, sand, friction, towel drying and reapplication, while keeping these clearly separate from the regulatory claim.

·         Where formulation risk warrants it, analyse UVB retention, UVA protection factor and critical wavelength separately after immersion.


What science tells us about films in water

Research shows that water attacks sunscreen films in more than one way. In a 2015 study in the International Journal of Cosmetic Science, Puccetti described two distinct stress sources: “high surface tension stress as the skin transits through the air/water interface and water diffusion into the film immersed in bulk water.” The study found that water-resistant sunscreens “generally perform well when immersed in bulk water even subjected to agitation, but they show a wide range of performances when considering their behaviour at the air/water interface,” with differences “more pronounced in salt water than tap water.” It also observed “a higher loss of filters… in the UV-A than in the UV-B.”

An earlier study by Puccetti and Fares (2014) compared tap, salt and chlorinated water and found “clear differences in water resistance values among the formulations tested, reflecting the importance of the formulation and the polymers used.”

Measurement itself can mislead. In a 2025 ring-test paper, Pissavini and colleagues, working with the Cosmetics Europe Sun Protection Methods Task Force, noted that “immersion can induce film rearrangement, altering UV absorbance without necessarily reducing active ingredient content. This may lead to atypical results, including apparent increases in SPF values post-immersion.” A credible protocol must therefore distinguish material loss, film heterogeneity and altered transmission.


Exploratory modules for research and development

Module

Recommended measure

Interpretive limit

Tap, saline and chlorinated water

Matched time, temperature and agitation conditions

A comparison tool; there is no harmonised Australian “sea-water proof” category.

Film retention

SPF and UVA before and after immersion, imaging or filter assay

Transmittance alone may reflect film rearrangement.

Air–water interface

Immersion and withdrawal cycles or a suitable device

Non-regulatory; requires full documentation.

Release

Analysis of wash-off water and degradation markers where feasible

Does not alone demonstrate marine safety.

New ISO projects to watch

Two new projects appear in the ISO work programme for cosmetics, as listed by the Swedish Institute for Standards committee page: ISO/AWI 26713, “Measurement of sun protection efficacy using integrated in vitro methods,” and ISO/AWI 26714, “Determination of Water Resistance using Hybrid Diffuse Reflectance Spectroscopy (HDRS) for ISO 23698.” Both are at stage 20.00, the preparatory stage. Neither establishes regulatory thresholds or labelling, and both should be monitored rather than relied upon. The European Commission, in its September 2026 JACOP release, has called for non-invasive methods to be extended to water-resistance claims.


Sources

·         Therapeutic Goods Administration, “Australian Regulatory Guidelines for Sunscreens”, Version 3.0, May 2023: https://www.tga.gov.au/sites/default/files/australian-regulatory-guidelines-for-sunscreens.pdf

·         Therapeutic Goods Administration, “Proposed adoption of AS/NZS 2604:2021”, April 2024: https://www.tga.gov.au/sites/default/files/2024-04/proposed-adoption-the-australian-new-zealand-sunscreen-standard-as-nzs-26042021.pdf

·         Accord Australasia, “Solving Sunscreen: From theory to practice – a thought starter”, March 2026: https://accord.asn.au/hubfs/Solving%20sunscreen%20challenges%20-%20theory%20to%20practice%20-%20a%20thought%20starter%20March%202026.pdf

·         Therapeutic Goods Administration, “How to use sunscreens”: https://www.tga.gov.au/resources/explore-topic/sunscreens/how-use-sunscreens

·         US Code of Federal Regulations, 21 CFR 201.327: https://www.ecfr.gov/current/title-21/chapter-I/subchapter-C/part-201/subpart-G/section-201.327

·         International Organization for Standardization, ISO 18861:2020: https://www.iso.org/standard/63659.html

·         Puccetti G, Int J Cosmet Sci, 2015;37(6):613–9: https://pubmed.ncbi.nlm.nih.gov/25940835/

·         Puccetti G, Fares H, Int J Cosmet Sci, 2014;36(3):284–90: https://pubmed.ncbi.nlm.nih.gov/24597927/

·         Pissavini M et al., Int J Cosmet Sci, 2025;47(5):851–863: https://pubmed.ncbi.nlm.nih.gov/40390693/

·         Swedish Institute for Standards, cosmetics committee work programme: https://www.sis.se/delta-och-paverka/tksidor/tk400499/sistk495/


About the Author

Dr Leslie Laquieze (PharmD, MSc, PhD, MBA) is a pharmacist-scientist and international expert in sunscreen testing, photoprotection, skin pharmacology and dermocosmetic claim substantiation. An expert member of the Australian Sunscreen Council, she has led Kosmoscience Europe since 2018, supporting the evaluation, substantiation and regulatory positioning of cosmetic and dermatological products across international markets.

This article reflects the opinion of Dr Leslie Laquieze. Readers are recommended to seek expert legal advice on all issues discussed.

 
 
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