How Do UV Filters Affect Corals? What the Evidence Shows and Where It Stops
Laboratory studies show that several organic UV filters, oxybenzone (benzophenone-3) above all, and uncoated zinc oxide nanoparticles can harm corals: bleaching, reduced photosynthesis, deformed larvae and death. Most of those effects were measured at concentrations above what is typically found in reef water, often in early life stages and sometimes only under light. Sunscreen is one local stressor among many, far behind ocean warming, and the US National Academies concluded in 2022 that the data were not yet sufficient to quantify the risk.
Published 26 October 2026. Sources checked on that date.
Key studies on UV filters and corals at a glance
Each row is one study. The values apply to the species, life stage and conditions shown and are not general thresholds.
| Study | Filter | Coral material | Main finding |
|---|---|---|---|
| Danovaro et al. 2008 | Sunscreen products, several organic filters | Field-collected branches | Rapid bleaching linked to viral activation; doses expressed per volume of product, hard to compare with later work |
| Downs et al. 2016 | Oxybenzone | S. pistillata planulae; cells of 7 species | Larval deformity EC20 6.5 µg/L in light; 24 h LC50 139 µg/L in light vs 779 µg/L in dark |
| He et al. 2019 | Four benzophenones | Larvae and adults of two species | Effects differed between species and life stages; larvae of one species affected where the other was not |
| Stien et al. 2019 | Octocrylene | P. damicornis adults | Accumulates as fatty-acid conjugates; polyp closure at 300 µg/L and above |
| Fel et al. 2019 | Several organic filters, zinc oxide | S. pistillata adults, 35 days | Zinc oxide reduced photosynthetic efficiency; most organic filters had little effect at tested levels; measured doses below nominal |
| Corinaldesi et al. 2018 | Zinc oxide, titanium dioxide | Acropora fragments | Uncoated zinc oxide nanoparticles caused severe bleaching; modified titanium dioxide caused minimal effects |
| Vuckovic et al. 2022 | Oxybenzone | Sea anemones and corals | Converted to glucoside conjugates that are phototoxic; symbiotic algae appeared to offer some protection |
Oxybenzone and other benzophenones
Oxybenzone (benzophenone-3) has the largest coral evidence base of any UV filter. Downs et al. (2014, 2016) reported deformity, DNA damage and death in Stylophora pistillata planulae, with effects much stronger in light than in darkness. Vuckovic et al. (2022) explained part of that light dependence: corals and anemones attach a sugar to oxybenzone, and the resulting conjugate generates damaging reactive species under sunlight.
Other benzophenones behave differently. He et al. (2019) compared four of them on two species and two life stages and found effects that varied by compound, species and stage, a reminder that results on one species cannot be assumed for another. That point is developed in multi-species coral testing.
Octocrylene and other organic filters
Evidence for most other organic filters is thinner and less consistent. Stien et al. (2019) showed that octocrylene builds up in Pocillopora damicornis tissue as fatty-acid conjugates and disturbs mitochondrial function. Fel et al. (2019), exposing Stylophora pistillata for 35 days, saw little effect from most organic filters at the levels tested, with an octocrylene effect only at their highest concentration.
The critical review by Mitchelmore et al. (2021) concluded that test designs across the literature are too heterogeneous to set robust coral thresholds for most organic filters, and that their own risk characterisation was preliminary.
Zinc oxide and titanium dioxide
Mineral filters are often presented as the coral-friendly default. The evidence is more nuanced. Corinaldesi et al. (2018) found that uncoated zinc oxide nanoparticles caused severe bleaching in Acropora fragments, while titanium dioxide with a modified surface caused minimal effects. Fel et al. (2019) also recorded reduced photosynthetic efficiency in Stylophora pistillata exposed to zinc oxide.
Particle size, coating and dispersion change how a mineral filter behaves in seawater. The practical conclusion for a formulator is that a mineral label, on its own, is not evidence about corals.
How do lab doses compare with reef water?
This is where many headlines go wrong. Downs et al. (2016) reported oxybenzone in US Virgin Islands bays between 75 µg/L and 1.4 mg/L, and between 0.8 and 19.2 µg/L at Hawaiian sites. A later survey of Hawaiian coastal water by Mitchelmore et al. (2019) measured oxybenzone between 0.2 and 136 ng/L, roughly a thousand times lower, and up to 241 ng/g dry weight in coral tissue.
The two sets of numbers come from different sites, dates and sampling methods and should not be averaged together. Concentrations vary strongly with swimmer density, time of day, water exchange and distance from the beach.
Reading the evidence: most laboratory effect levels sit above typical open reef water, but some measured hotspots overlap with them. Risk is therefore local and site-specific, which is consistent with the conclusion of the US National Academies (2022) that existing data could not quantify it and that an ecological risk assessment was needed.
Sunscreen among other stressors on coral reefs
The Global Coral Reef Monitoring Network estimated that hard coral cover fell from 33.3% in 2009 to 28.8% in 2018, a loss of about 14%, driven mainly by repeated warming-related bleaching. Land-based runoff, sediment, nutrients, overfishing and disease add to that pressure. Sunscreen filters are a local chemical stressor within this picture, not its main cause.
That is not a reason to ignore them. Contaminants can lower a coral's tolerance to heat, as Negri and Hoogenboom (2011) showed for other chemicals, and a formulation is one of the few stressors a cosmetics company directly controls.
What this means for sunscreen formulators
- •Ingredient bans are a floor. Laws in Hawaii, the US Virgin Islands and Palau list specific filters; they say nothing about the rest of a formula. The laws are summarised in what reef-safe certification means.
- •Test the finished product. Ingredient data cannot capture interactions in a formulation, so a live-coral test of the formula answers a different question from a literature review.
- •Claim what was tested. Environmental claims should state the test, species and conditions. Absolute claims that a product is harmless to reefs go beyond what any test can show.
At ReefTox, every cosmetics engagement starts with a free predictive pre-evaluation, included with a paid test, that screens the formulation before any coral is exposed. The live-coral options are described in coral testing for sunscreens, and SPF ingredients can be tested on their own with ReefFilter.
Frequently asked questions
Do sunscreens kill coral reefs?
The evidence does not support that headline. Some UV filters harm corals in the laboratory, mostly at concentrations above typical reef water and in sensitive life stages. On a global scale, warming-driven bleaching is the dominant cause of coral loss. Sunscreen can still matter locally, in crowded bays and lagoons with little water exchange.
Is oxybenzone toxic to corals?
In laboratory studies, yes. Downs et al. (2016) reported deformities in Stylophora pistillata planulae with an EC20 of 6.5 µg/L under light, and Vuckovic et al. (2022) showed that corals and anemones convert oxybenzone into conjugates that become toxic in light. Measured concentrations in Hawaiian coastal water by Mitchelmore et al. (2019) were in nanograms per litre, well below most effect levels.
Are mineral sunscreens with zinc oxide or titanium dioxide better for corals?
Not automatically. Corinaldesi et al. (2018) found that uncoated zinc oxide nanoparticles caused severe bleaching in Acropora, while titanium dioxide with a modified surface caused minimal effects. Particle type, size and coating matter, so a mineral label alone does not settle the question.
What about octocrylene and other organic filters?
The data are thinner. Stien et al. (2019) found that octocrylene accumulates in Pocillopora damicornis tissue as fatty-acid conjugates, with polyps closing at 300 µg/L and above. Fel et al. (2019) saw an effect of octocrylene on Stylophora pistillata only at the highest concentration they tested. Data on many newer filters remain limited.
Does removing two filters make a sunscreen harmless to corals?
No ingredient list can show that. Other filters, emollients, preservatives and the interaction between them are not covered by oxybenzone and octinoxate bans. Only a test of the finished formulation on live coral measures its actual effect, under stated conditions.
Sources
Peer-reviewed and agency sources, checked 26 October 2026. This page summarises published research and is not a risk assessment of any specific product.
- Danovaro R et al. (2008). Sunscreens cause coral bleaching by promoting viral infections. Environmental Health Perspectives 116:441-447
- Downs CA et al. (2016). Toxicopathological effects of the sunscreen UV filter, oxybenzone (benzophenone-3), on coral planulae and cultured primary cells and its environmental contamination in Hawaii and the U.S. Virgin Islands. Archives of Environmental Contamination and Toxicology 70:265-288
- Downs CA et al. (2014). Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral Stylophora pistillata. Ecotoxicology 23:175-191
- He T et al. (2019). Comparative toxicities of four benzophenone ultraviolet filters to two life stages of two coral species. Science of the Total Environment 651:2391-2399
- Stien D et al. (2019). Metabolomics reveal that octocrylene accumulates in Pocillopora damicornis tissues as fatty acid conjugates and triggers coral cell mitochondrial dysfunction. Analytical Chemistry 91:990-995
- Fel J-P et al. (2019). Photochemical response of the scleractinian coral Stylophora pistillata to some sunscreen ingredients. Coral Reefs 38:109-122
- Corinaldesi C et al. (2018). Impact of inorganic UV filters contained in sunscreen products on tropical stony corals (Acropora spp.). Science of the Total Environment 637-638:1279-1285
- Vuckovic D et al. (2022). Conversion of oxybenzone sunscreen to phototoxic glucoside conjugates by sea anemones and corals. Science 376:644-648
- Mitchelmore CL et al. (2019). Occurrence and distribution of UV-filters and other anthropogenic contaminants in coastal surface water, sediment, and coral tissue from Hawaii. Science of the Total Environment 670:398-410
- Mitchelmore CL et al. (2021). A critical review of organic ultraviolet filter exposure, hazard, and risk to corals. Environmental Toxicology and Chemistry 40(4):967-988
- National Academies of Sciences, Engineering, and Medicine (2022). Review of Fate, Exposure, and Effects of Sunscreens in Aquatic Environments and Implications for Sunscreen Usage and Human Health
- Negri AP, Hoogenboom MO (2011). Water contamination reduces the tolerance of coral larvae to thermal stress. PLoS ONE 6(5):e19703
- Global Coral Reef Monitoring Network (2021). Status of Coral Reefs of the World: 2020. UNEP / ICRI / AIMS
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