Essential Protection… With Hidden Limits
Sunscreens have become a daily essential. They protect the skin from sunburn, slow down premature aging, and reduce the risk of skin cancer caused by ultraviolet radiation. For years, dermatologists and health authorities have strongly encouraged their use.
But behind this essential protection, some scientific concerns are beginning to emerge. Several chemical UV filters commonly used in sunscreens may not remain stable once exposed to sunlight. Under UVA and UVB radiation, certain compounds can gradually break down, lose part of their protective capacity, and generate new chemical byproducts that are still poorly understood.
When Sunlight Breaks Down UV Filters
A study published in the Journal of Investigative Dermatology examined how several UV filters behaved after exposure equivalent to a full day in the sun.
Researchers found that some molecules, particularly avobenzone, rapidly lost their ability to absorb UVA radiation after irradiation. In practical terms, this means that the longer the sun exposure lasts, the weaker the protection may become.
This phenomenon, known as photodegradation, raises important questions about the real stability of some sunscreen products. A sunscreen may display a high SPF when applied, yet provide significantly lower protection only a few hours later.
Scientists also detected the formation of chemical byproducts created during the degradation process. While the long-term effects of these compounds remain largely unknown, their presence raises concerns about both safety and product durability.
Not all UV filters reacted the same way. Benzophenones, for example, appeared far more stable under UV exposure, highlighting how crucial formulation choices are in determining sunscreen performance over time.
An Invisible Pollution Entering Aquatic Ecosystems
The issue does not stop at human skin. Every summer, large amounts of sunscreen chemicals are released into the environment.
During swimming, part of the sunscreen applied to the body washes directly into oceans, lakes, and rivers. The remainder is rinsed off in showers and eventually reaches wastewater treatment plants.
The problem is that these facilities often struggle to fully remove UV filters from wastewater. As a result, these compounds are now commonly detected in surface waters, coastal environments, marine sediments, and aquatic organisms.
Because many UV filters are highly lipophilic, they tend to accumulate in living tissues rather than dissolve harmlessly in water. This bioaccumulation potential has become a growing concern for environmental scientists.
Concerning Effects Observed in Fish
A second study, published in Ecotoxicology and Environmental Safety, investigated the effects of two organic UV filters on freshwater fish.
Researchers found significant accumulation of these compounds in the liver, brain, and kidneys of exposed fish. More importantly, the substances were not biologically neutral.
The fish showed enzymatic disturbances associated with oxidative stress, along with inhibition of neurological functions essential for normal biological activity. In other words, these chemicals did not simply remain present in the organism — they actively altered its biological functioning.
The authors highlighted potential risks for nervous system function and cellular balance in aquatic species. Although the long-term ecological consequences are still being studied, these findings reinforce growing concerns about the environmental impact of organic UV filters.
Toward More Sustainable Sunscreens
These studies reveal a striking modern paradox. Sunscreens remain essential for protecting human health, yet some of the molecules used for decades are now showing clear limitations.
The challenge for the coming years will be to develop UV filters that are not only effective, but also photostable and environmentally safer. Researchers and cosmetic companies are already exploring new formulations designed to maintain long-lasting protection while reducing ecological harm.
Because the sunscreen of the future will likely need to do more than protect our skin. It will also need to protect the ecosystems these chemicals inevitably end up affecting.
Sources
Tarras-Wahlberg N. et al., Changes in Ultraviolet Absorption of Sunscreens After Ultraviolet Irradiation, Journal of Investigative Dermatology, 1999.
Ma B. et al., Bioconcentration and multi-biomarkers of organic UV filters (BM-DBM and OD-PABA) in crucian carp, Ecotoxicology and Environmental Safety, 2017.