Endocrine disruptors are substances capable of interfering with hormonal signalling, potentially affecting growth, reproduction, metabolism, or development. In our previous article, we followed sunscreen UV filters from our skin to rivers, lakes, and oceans. But their journey doesn’t end there. Once these chemicals enter aquatic ecosystems, they continue interacting with living organisms and growing evidence suggests that some may interfere with hormonal systems in fish and other aquatic species.
A Widespread Environmental Contamination
The presence of sunscreen UV filters in the environment is no longer a hypothesis, it is now well documented.
A Swedish national environmental monitoring program detected multiple UV filters in recreational waters, wastewater treatment plant effluents, sediments, and even wild fish. Some compounds were also found in remote lakes with limited human activity, suggesting that their distribution extends far beyond popular swimming areas.
Researchers identified two main pathways through which these chemicals enter aquatic ecosystems: direct release during swimming and indirect discharge through wastewater. Since conventional wastewater treatment plants are not specifically designed to remove these compounds, significant amounts can eventually reach rivers, lakes, and coastal waters.
These findings illustrate that environmental exposure to UV filters is widespread and continuous rather than restricted to isolated recreational sites.
From Environmental Contaminants to Endocrine Disruptors
Detecting UV filters in the environment is one thing. Understanding how they affect living organisms is another.
Several experimental studies cited in the Swedish report indicate that some chemical UV filters can interfere with the endocrine system of aquatic species. These substances have been shown to alter hormonal pathways involved in growth, development, and, most importantly, reproduction.
Reported effects include changes in vitellogenin production, a well-established biomarker of endocrine disruption in fish, as well as abnormalities in reproductive organs and reduced fertility in several aquatic species.
Although these findings concern wildlife rather than humans, they raise important questions about the long-term ecological consequences of chronic environmental exposure.
The Thyroid: A Newly Identified Target
More recent experimental research has expanded our understanding of how UV filters may affect endocrine function.
A study conducted on zebrafish embryos investigated two commonly used sunscreen ingredients: avobenzone and octinoxate. The researchers found evidence of disruption of the hypothalamic–pituitary–thyroid (HPT) axis, the hormonal system responsible for regulating thyroid function.
Exposure altered thyroid hormone levels and modified the expression of several genes involved in endocrine regulation. The study also reported delayed hatching and developmental abnormalities at the highest exposure concentrations.
The authors emphasize that these findings were obtained using an experimental animal model and should not be directly extrapolated to humans. Nevertheless, the study provides further evidence that certain UV filters are biologically active and capable of interfering with endocrine regulation in aquatic organisms.
Climate Change Could Make the Problem Worse
If certain UV filters already affect endocrine and reproductive pathways, an important question emerges: could other environmental stressors amplify these effects? Rising water temperatures provide an ideal case study.
Aquatic organisms are simultaneously exposed to chemical contaminants and increasing temperatures associated with climate change. Scientists are therefore increasingly investigating how these multiple stressors interact.
A 2023 study examined the combined effects of avobenzone and elevated seawater temperature on the Mediterranean mussel (Mytilus galloprovincialis), an important bioindicator species for coastal ecosystems.
The researchers found that warmer water significantly enhanced several adverse biological effects associated with avobenzone exposure. Mussel sperm exhibited increased oxidative stress, greater cellular damage, DNA alterations, and reduced motility when both stressors were combined.
These findings suggest that climate change may amplify the biological effects of certain UV filters, particularly during the summer months when sunscreen use reaches its peak.
While additional studies are needed to determine whether similar interactions occur in other aquatic species, the results highlight the importance of considering climate change when evaluating the environmental risks of chemical contaminants.
Health Authorities Are Also Paying Attention
These concerns are not limited to academic research.
The involvement of regulatory agencies illustrates that environmental risks associated with UV filters are no longer considered solely academic questions but are increasingly being incorporated into chemical risk assessment.
In France, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) has identified several UV filters, including octocrylene, octinoxate, and oxybenzone, as substances of concern for marine ecosystems under certain exposure conditions.
ANSES has also proposed a European restriction on the use of octocrylene in cosmetic products to reduce its environmental release.
Importantly, these assessments do not question the importance of sunscreen in preventing sunburn and reducing the risk of skin cancer. Instead, they reflect a broader evolution in safety assessment: UV filters are increasingly evaluated not only for their effectiveness in protecting human skin but also for their potential environmental impacts.
Protecting Our Skin Without Compromising Aquatic Life
The history of environmental toxicology repeatedly reminds us that biologically active chemicals often reveal their ecological consequences only after years of widespread use. UV filters are increasingly being recognized as biologically active compounds rather than inert cosmetic ingredients. Understanding what this means for aquatic ecosystems will require continued research, long-term environmental monitoring, and a willingness to integrate emerging scientific evidence into future regulatory decisions.
Protecting human health and protecting aquatic ecosystems should not be competing goals. The next generation of sunscreen technologies will ideally provide effective UV protection while minimizing unintended impacts on the environment.
References
- Swedish National Screening Programme (2009). Results from the Swedish National Screening Programme – Subreport 3: UV Filters.
- Ma, T. et al. (2022). Effects of avobenzone and octinoxate on the hypothalamic–pituitary–thyroid axis in zebrafish larvae.
- Bordalo, D. et al. (2023). Will warmer summers increase the impact of UV filters on marine bivalves?
- ANSES (2023). Chemical pollution and coral reefs. Proposal to restrict octocrylene in cosmetic products.