Oxybenzone and Avobenzone Byproducts — Public Health and Regulatory Considerations

Prepared by:  Dr. Abhinandan Chowdhury ( Rocky)

Date: 09/07/25

Executive Summary

Oxybenzone (benzophenone-3) and avobenzone are widely used chemical UV filters in sunscreens. While these compounds are effective for skin cancer prevention, emerging research highlights that their breakdown products—especially in chlorinated swimming pools—may pose potential risks to respiratory and systemic health. Although direct evidence linking the parent compounds to asthma or respiratory disease is lacking, the formation of volatile and potentially toxic disinfection byproducts (DBPs) raises legitimate public health concerns. Given their additional scrutiny for endocrine, reproductive, and systemic effects, it is prudent for regulatory authorities to promote precaution, further research, and public awareness regarding these UV filters and their transformation products^[1][2].

Key Points of Concern

1. Formation of Potentially Harmful Byproducts

• Chemical Transformation: When oxybenzone and avobenzone enter chlorinated pool water, they react to form a range of chlorinated and brominated byproducts, including chlorinated phenols, acetophenones, and other volatile compounds^[1][2].

• Volatility and Exposure: Many of these byproducts are volatile and can accumulate in the air above indoor pools, increasing the risk of inhalation exposure for swimmers, children, athletes, and pool workers^[2].

• Known Respiratory Irritants: Some of these transformation products are established respiratory irritants or have genotoxic properties, adding to the overall burden of disinfection byproducts in pool environments^[1].

2. Indirect Evidence of Health Risks

• Swimming Pool DBPs and Asthma: Multiple studies confirm that general disinfection byproducts in pools, especially trichloramine, are associated with increased asthma risk and respiratory symptoms in children and frequent swimmers.

• UV Filter Contribution: While the specific contribution of oxybenzone and avobenzone byproducts to these effects is not fully quantified, their presence adds to the chemical complexity and potential hazard of pool air^[1][2].

• Systemic Health Scrutiny: Both compounds have also been under regulatory review for systemic absorption, endocrine disruption, and reproductive/developmental toxicity, indicating a broader safety concern beyond respiratory endpoints.

3. Regulatory and Scientific Gaps

• Lack of Direct Human Data: No current epidemiological studies directly link sunscreen-derived UV filters to asthma or respiratory disease, but the theoretical risk from their byproducts is scientifically plausible and supported by mechanistic studies ( SEE BELOW)^[1][2].

• Regulatory Silence: Major regulatory authorities (FDA, TGA, SCCS) have not yet addressed the specific issue of UV filter-derived DBPs in pool environments, focusing instead on systemic and endocrine effects.

• Need for Targeted Research: There is a critical need for:

  • Air monitoring studies in pools with high sunscreen use

  • Toxicological assessment of identified byproducts

  • Epidemiological studies in vulnerable populations (children, athletes, pool workers)

Mechanistic Pathway: How Oxybenzone and Avobenzone Contribute to DBPs Linked to Respiratory Effects

• Chlorination and Oxidation: Both oxybenzone and avobenzone react readily with free chlorine and, in some cases, bromide ions present in pool water. This reaction leads to electrophilic substitution and oxidation, producing a range of chlorinated and brominated aromatic compounds, including chlorinated phenols, chlorinated acetophenones, and trihalomethanes (THMs)^[1][2].

• Formation of Volatile Byproducts: Many of these DBPs are volatile organic compounds (VOCs). Once formed, they can off-gas from the water surface into the air above the pool, especially in indoor environments with limited ventilation. This creates a microenvironment rich in airborne DBPs, including well-known respiratory irritants such as trichloramine (NCl₃) and various chlorinated aromatics.

• Inhalation Exposure: Swimmers, particularly children and athletes who breathe deeply and frequently at the water’s surface, as well as pool staff, are at risk of inhaling these volatile byproducts. Inhalation of DBPs can irritate the upper and lower respiratory tract, trigger bronchial inflammation, and increase airway hyperresponsiveness.

• Link to Asthma and Respiratory Symptoms: Epidemiological studies have established that exposure to DBPs—especially trichloramine and certain chlorinated organics—in indoor pool environments is associated with increased rates of asthma, wheezing, and other respiratory symptoms in children and frequent pool users. While most research has focused on DBPs formed from nitrogenous organic matter (like sweat and urine), the addition of sunscreen-derived aromatic compounds (oxybenzone, avobenzone) increases the diversity and potential toxicity of the DBP mixture, potentially compounding respiratory risks^[1][2].

In summary: Oxybenzone and avobenzone, through their transformation into volatile DBPs in chlorinated water, contribute to the chemical burden of indoor pool air. These byproducts, when inhaled, can irritate the respiratory tract and are mechanistically linked to the increased prevalence of asthma and respiratory symptoms observed in swimmers and pool workers. The exact contribution of sunscreen-derived DBPs to overall respiratory risk remains an active area for further research, but the mechanistic plausibility is well-supported by current chemical and toxicological evidence^[1][2].

Recommendations for Regulatory Attention

• Promote Research: Encourage and fund studies that assess the real-world concentrations and toxicity of oxybenzone and avobenzone byproducts in pool environments.

• Public Awareness: Develop educational materials for swimmers, parents, and pool operators about the importance of pre-swim showering, proper pool ventilation, and the potential risks of chemical sunscreen use in pools.

• Precautionary Principle: Consider interim guidance favoring mineral-based sunscreens (zinc oxide, titanium dioxide) in public pools, especially for children and frequent swimmers, until more definitive evidence is available.

• Review Regulatory Frameworks: Re-examine sunscreen ingredient approvals and labeling requirements to reflect emerging science on transformation products and indirect health risks.

• Educating consumers to consider mineral-based sunscreens (non-nano zinc oxide), which are inert and do not react with chlorine, for swimming in indoor pools.

Conclusion

Oxybenzone and avobenzone remain under scrutiny for their already known health and environmental hazards. Added to those, potential harmful byproducts in chlorinated water environments justifies increased scientific, regulatory, and public health attention. The absence of direct human evidence should not preclude precautionary action, especially given the established risks of pool DBPs and the broader systemic concerns associated with these UV filters. Regulatory authorities are urged to prioritize research, risk communication, and evidence-based policy to ensure the continued safety of sunscreen use in all aquatic settings.

References

1. Wang, L., et al. (2016). Chlorination of oxybenzone: Kinetics, transformation, disinfection byproducts formation, and genotoxicity changes. Chemosphere, 154, 521-527.

2. Krasner, S.W., et al. (2020). Identification of avobenzone by-products formed by various disinfectants in different types of swimming pool waters. Environment International, 136, 105479.

3. Scientific Committee on Consumer Safety (SCCS). (2021). Opinion on Benzophenone-3 (Oxybenzone), SCCS/1622/20. European Commission.

4. U.S. Food and Drug Administration. (2021). Sunscreen drug products for over-the-counter human use — Proposed administrative order. Federal Register, 86 FR 53309.

5. Klavarioti, M., et al. (2017). Stability and removal of selected avobenzone's chlorination products. Chemosphere, 173, 107-114.

6. Bernard, A., & Delgado, A. (2012). Health effects of exposure to chlorination by-products in swimming pools. Annali dell'Istituto Superiore di Sanità, 48(4), 387-396.

7. Manasfi, T., et al. (2017). Degradation of organic UV filters in chlorinated seawater swimming pools. Environmental Science & Technology, 51(22), 13263-13271.

8. Bernard, A., et al. (2006). Chlorinated pool attendance, atopy, and the risk of asthma during childhood. Environmental Health Perspectives, 114(10), 1567-1573.

9. Therapeutic Goods Administration. (2025). Literature search and summaries of seven sunscreen active ingredients. Australian Government Department of Health.