Recent court rulings in both Europe and the United States have overturned classifications of titanium dioxide as potentially carcinogenic, raising significant questions about the intersection of science and regulatory authority. On August 1, 2025, Europe’s highest court ruled that regulators had not adequately considered all relevant factors when determining the carcinogenicity of titanium dioxide, while a U.S. federal court followed suit on August 12, 2025, rejecting warning requirements for the substance in cosmetics.
Titanium dioxide, a white mineral powder found in products ranging from paint and sunscreen to food, was long deemed safe. However, the rise of nanomaterials in the early 2000s led to growing concerns about the safety of its nanoparticle form. Research indicated that these nanoparticles might interact with biological systems differently than larger particles, prompting the International Agency for Research on Cancer (IARC) to classify titanium dioxide as “possibly carcinogenic to humans” in 2010.
This classification was predominantly based on studies conducted on rats, which showed a correlation between high concentrations of titanium dioxide particles and increased lung tumors. In response, California listed specific airborne titanium dioxide particles under its Proposition 65 in 2011, requiring warning labels on products containing the substance. The European Commission followed suit in 2019, mandating similar warnings across Europe.
Scientific Uncertainty Underpins Legal Challenges
While the implementation of warning labels may seem decisive, it masks substantial uncertainty in the scientific community. The IARC classification initiated widespread debate about the relevance of animal studies in predicting human cancer risk. Critics pointed out that while animal studies can indicate potential harm, translating these results to humans is fraught with challenges.
Moreover, research into the toxicity of nano titanium dioxide continues to yield inconsistent findings, with various factors influencing outcomes, including exposure levels and individual susceptibility. This scientific complexity provided fertile ground for legal challenges from industry groups contesting the carcinogenic classifications, arguing that regulators had misinterpreted the science.
The courts ultimately sided with the industry. The ruling on August 1, 2025, highlighted that European regulators had utilized an incorrect particle density value when assessing lung overload in rats, undermining the reliability of the animal data to predict human cancer risk. Consequently, the court nullified the carcinogenic classification.
In the United States, the federal court acknowledged that while the warnings about titanium dioxide were technically accurate, they lacked the necessary scientific basis to be deemed “purely factual and uncontroversial.” The court noted that significant scientific debate persisted regarding the safety of the substance.
Implications for Regulatory Science
These rulings mark a pivotal shift in how regulatory science is approached. Initially, U.S. and European agencies prioritized precautionary measures in their classifications, recognizing the limitations of animal studies prior to human evidence. The courts’ decisions, however, call into question the role of the judiciary in interpreting scientific findings.
Critics argue that judges, lacking specialized scientific training, should not overrule the expertise of scientific committees on complex issues. The tensions between scientific assessment and legal authority raise important questions: How deeply do judges understand the science they adjudicate? Should they have the power to challenge scientific determinations made by expert panels?
Further complicating the issue is the broader dilemma of when regulators should act on complex scientific evidence. Ethical considerations prevent controlled human studies, and the necessity for immediate public health protections can clash with the aspiration for definitive proof—a challenging balance to strike.
As emerging technologies increasingly permeate daily life, the challenges posed by scientific uncertainty may become more pronounced within legal contexts. Ensuring that legal institutions are equipped to navigate these complexities is paramount. Collaborative efforts between scientific and legal experts will be essential in addressing the evolving landscape of regulatory science.
Rachael Wakefield-Rann and Sarah Wilson, both scholars in the field, have disclosed no relevant affiliations beyond their academic appointments, ensuring their analyses remain grounded in impartial research.
