Swimmers can protect lake health with sunscreen choice

It is important to protect your skin from too much sun. You can do this by limiting your exposure time, covering up, and using sunscreen. If you use sunscreen before swimming, please consider which active ingredients it contains, as some are better for the lake and its inhabitants than others.

Zinc oxide (ZnO) and titanium dioxide (TiO2), often used in combination, are minerals which form a physical UV filter. Mineral sunscreens are white when applied and don’t absorb through your skin. These traditional sunscreens have been used effectively for decades, and are safe for lake life. Mineral sunscreens are classified as Natural Health Products in Canada (1).

Some mineral sunscreens use nanoparticle formulations of zinc oxide and titanium dioxide. These sunscreens are effective and they are safe for you (2). As nanoparticle sunscreens are relatively new, the long-term effects on freshwater ecosystems are not well understood, but experiments have demonstrated potential negative effects on microbes, algae, invertebrates and fish (3). Health Canada does not require specific labeling on nanoparticle sunscreens, but you may find the term micronized, or a claim that the sunscreen is transparent when applied.

Other sunscreens use a combination of ingredients to form a chemical UV filter. Common examples are: avobenzone, homosalate, octisalate, octocrylene and oxybenzone, but there are many more approved for use in Canada, and all chemical sunscreens are classified as non-prescription drugs (1). These chemicals persist in the lake, and many have endocrine-disrupting effects, meaning they interact with hormone signalling. This can lead to many detrimental effects on development, reproduction and behaviour in marine organisms from microbes to fish.3 Notably, chemical sunscreens are likely responsible for extensive coral bleaching, which has led to a ban on some sunscreen ingredients in Hawaii and the Virgin Islands. Research in freshwater environments is limited, but recent work has shown that chemical sunscreens can have behavioural and toxic effects on freshwater insects, which are a major source of food for fish, so potentially put the whole ecosystem at risk (4).

Mineral sunscreens are also known as inorganic, in contrast to the organic chemical sunscreens. But don’t let the organic label fool you: it is used here in the chemical sense meaning carbon-based, rather than the agricultural sense of being produced without chemical additives.

Chemical sunscreens will eventually find their way into the water, if not from swimming in the lake, then by washing into your septic system, or into a municipal sewer, from where they pass into the marine environment (5). Whatever their destination, they can be detrimental, even in trace amounts. Nanoformulations of mineral sunscreens also persist in the environment and wastewater, where their effects can depend on the various possible chemical treatments used in preparation of the nanoparticles (6).

So please, choose mineral sunscreens with only non-nano zinc oxide and titanium dioxide as active ingredients, to support healthy ecosystems! Sol Mate, made by Sea Wench Naturals in Tofino and available at Natureworks, is a great option.

— Joanne Whitehead

1. Health Canada: Health Products and Food Branch, 2026-02-27. Primary Sunscreen Monograph.
2. Bai X, Yan J, Gilchrest BA. Next-Generation Zinc Oxide-Based Sunscreens: Molecular Characteristics and Advantages. J Invest Dermatol. 2024 Feb;144(2):430-434.e1. doi: 10.1016/j.jid.2023.07.020.  ‍  
3. Hodge AA, Hopkins FE, Saha M, Jha AN. Ecotoxicological effects of sunscreen derived organic and inorganic UV filters on marine organisms: A critical review. Mar Pollut Bull. 2025 Apr;213:117627. doi: 10.1016/j.marpolbul.2025.117627.  
4. Boyd A, Stewart CB, Philibert DA, How ZT, El-Din MG, Tierney KB, Blewett TA. A burning issue: The effect of organic ultraviolet filter exposure on the behaviour and physiology of Daphnia magna. Sci Total Environ. 2021 Jan 1;750:141707. doi: 10.1016/j.scitotenv.2020.141707.  Press release
5. Ramos S, Homem V, Alves A, Santos L. A review of organic UV-filters in wastewater treatment plants. Environ Int. 2016 Jan;86:24-44. doi: 10.1016/j.envint.2015.10.004.  
6. Labille J, Catalano R, Slomberg D, Motellier S, Pinsino A, Hennebert P, Santaella C and Bartolomei V. Assessing Sunscreen Lifecycle to Minimize Environmental Risk Posed by Nanoparticulate UV-Filters – A Review for Safer-by-Design Products. Front. Environ. 2020. Sci. 8:101. doi: 10.3389/fenvs.2020.00101