Exposure to the sun’s rays can harm human skin by causing sunburn, photo-aging, and increasing the risk of developing skin cancer. Sunscreen is one critical tool to help mitigate these harms.
But when people wear sunscreens, some of that sunscreen can end up in the water. As a result of their use in sunscreens and other consumer products, these ingredients have been detected in the water, sediments, and living things along coasts, in rivers, and in lakes.
Although the presence of sunscreen chemicals in the environment doesn’t necessarily indicate that they are causing harm, it has led to a rapid increase in research on their potential environmental impacts, and to a ban on certain sunscreen ingredients in Hawaii, the U.S. Virgin Islands, and several other locations.
But the science on sunscreens is still evolving. Environmental exposure and hazard data on sunscreen ingredients are limited, and there is not widespread agreement about whether the available research sufficiently supports conclusions that individual ingredients have, or do not have, negative effects on aquatic organisms.
How can scientists and regulators understand potential risks to aquatic environments to allow consumers to make informed choices about using sunscreen to protect their health while also protecting the health of the environment?
The active ingredients in sunscreens are ultraviolet (UV) filters, which are compounds that protect the skin by absorbing, reflecting, and/or scattering the sun’s ultraviolet rays.
Seventeen different UV filters can be used in products sold in the United States, although a handful are not currently in use. They are usually found in combination so that your sunscreen can protect against the full ultraviolet spectrum.
UV filters are not all the same. Two are inorganic particles (also referred to as “physical” or “mineral” filters) : titanium dioxide and zinc oxide. The remainder are organic (carbon-based) chemicals. The UV filters display a wide range of physical and chemical properties, such as their solubility, their stability under UV radiation, and their ability to biodegrade. These properties influence their variable fates in the environment and toxicity to aquatic organisms.
Sunscreen active ingredients have been detected in water bodies, aquatic sediment, and aquatic organisms. The physical characteristics of the water body into which sunscreens are released is one influence on the amount of UV filters in a given area and therefore how they impact aquatic life in that water. The amount of water exchange is one factor as shown in the figure and images below.
There is a pattern emerging to their occurrence, where they are more likely to be found near recreational areas in water bodies with minimal water exchange, such as coastal bays or coves with sheltered beaches. However, there is more to learn about the spatial and temporal variability of their occurrence, and some UV filters have been monitored very little.
Laboratory observations show that, in high enough concentrations, some UV filters can be toxic to algal, invertebrate, and fish species. Impacts to corals have been measured and are of particular concern due to their sensitivity to stress, their high value to humans from provision of food to cultural traditions, and their proximity to recreational activity. However, it is challenging to study corals, in part due to their unique biological characteristics, such as the relationship between the coral host and their symbiotic algae and microbiome. Ideally, information would be available across a range of species and life stages for all UV filters to identify thresholds of concern for the most sensitive organisms.
The challenge for understanding the effects of sunscreens on aquatic environments is determining whether and under what conditions individual or mixtures of UV filters are a risk to organisms and ecosystems—and how UV filters may act either alone, or in combination with other environmental stressors. Then, scientists need to understand where these particular conditions might occur.
An ecological risk assessment (ERA) is a process to identify particular exposure settings in which a stressor—in this case, UV filters—could be the cause of environmental concern. To carry out the ERA, scientists will integrate information about exposures in the environment with information about adverse affects. The more information that is available, the more robust the ERA will be, and thus continuing to conduct research in this area is critical.
Most of the research carried out to date has taken place in laboratories, but the characteristics of aquatic environments will undoubtedly influence the fate and effect sunscreen ingredients have on the environment. This makes it challenging to generalize about UV filters and their potential risks.
For example:
The existing bans on certain UV filters may be considered precautionary in principle, in that they protect the environment against a potential threat now, rather than wait for more data. This approach has raised questions, though, about the potential human health implications resulting from reduced availability of some widely-used UV filter ingredients.
The relationship between UV radiation and skin cancer risk is well established, particularly for fair-skinned populations. Only a third of the U.S. population uses sunscreen regularly (though use is higher during outdoor activities and at the beach), and most people use less sunscreen than is recommended. There are concerns that consumers may use sunscreen at reduced frequency or in reduced quantities based on perceived environmental impacts or restrictions on certain UV filters that reduce availability of consumer-preferred formulations. If so, this could have negative implications for human health.
Sunscreens are one part of a recommended sun protection regimen that also includes the use of protective clothing, hats, and sunglasses, as well as avoiding the sun and seeking shade where possible. Sunscreen may be the only option for full body protection during certain outdoor recreation or employment activities, and similar to sunscreen, only about a third of the U.S. population employ these other measures. However, these behaviors provide a supplement or alternative to sunscreen when adopted.
Consumers concerned with environmental impacts might seek “reef-safe” or other similarly branded or certified products; however, there is no regulatory definition or oversight for what constitutes “reef-safe” that ensures it is scientifically meaningful or accurate. Despite that, these terms are prominently visible on the internet, in advertising, and on labels on sunscreen packaging. A 2019 analysis of 97 popular sunscreens found that 49 percent of those labeled “reef-safe” did not meet the criteria of the legislative ban in Hawaii.
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This resource is based on a report from the National Academies of Sciences, Engineering, and Medicine that reviews the current research on the effects of sunscreens on aquatic ecosystems. The report’s goal is to help scientists and policy makers improve understanding about the use of sunscreens so the public can make choices that protect both environmental and human health.
Read the Report