January 12, 2026 | Erin Bluvas, bluvase@sc.edu

New research from the Department of Environmental Health Sciences explores how common sunscreen ingredients behave under light exposure. Led by associate professor Eric Vejerano, the team tested seven commercially available sunscreens (including four mineral-based formulas) and found that every sample produced persistent free radicals (PFRs) when exposed to artificial light. The study,  published in Environmental Science & Technology Letters, provides new insight into sunscreen photochemistry and may help guide future evaluations of product performance and safety.

 

Every commercially available suncreen tested by the lab produced persistent free radicals when exposed to artificial light.

“We already knew that light exposure causes mineral sunscreens to generate transient free radicals, but this study has revealed they can also produce long-lived free radicals,” Vejerano says. “This can happen during routine sunscreen use with unknown impacts to human and environmental health.”

Arriving at the Arnold School in 2017, Vejerano’s expertise centers on air quality –more specifically, how nanoparticles interact with environmental pollutants. A member of the South Carolina SmartState Center for Environmental Nanoscience and Risk (CENR), his National Science Foundation-funded research examines the nature, sources, and impacts of persistent free radicals.

Since the 1950s, most PFR research has focused on particles created through industrial processes such as combustion and thermal reactions. Vejerano’s lab has expanded this work by identifying the presence of biogenic PFRs in unexpected sources like leaves, an important contributor to PFRs since 82% of the Earth’s land biomass is comprised of plants.

In this latest groundbreaking study, Vejerano and his team were the first to demonstrate that commercial sunscreens produce PFRs that persist long after light exposure has ended. Using a variety of lab tests, the researchers found that while light exposure increases the generation of PFRs, the introduction of water led to significantly reduced PFR output for most of the sunscreens. However, one of the samples led to enhanced PFR formation after water was introduced, raising concerns about the impact on aquatic environments such as coral reefs.

The team estimates that approximately 10 PFRs may form per gram of sunscreen. At 20-40 grams for full-body coverage, this calculation suggests the creation of 200-400 PFRs per typical application, though the exact amount and behavior likely vary across formulations.

“Our results highlight the need to reevaluate the continued use of certain sunscreen formulations that are prone to producing PFRs,” Vejerano says. “These alternatives may preserve UV protection while reducing human and environmental health risks.”

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