Recent court rulings in both the United States and Europe have overturned regulatory classifications of titanium dioxide as possibly carcinogenic, raising questions about how science informs legal decisions. On August 1, 2025, Europe’s highest court sided with the titanium dioxide industry, stating that regulators failed to consider all relevant scientific evidence. Just days later, on August 12, a US federal court struck down similar warning requirements for cosmetics containing titanium dioxide, citing the underlying science as controversial.
The substance at the center of these legal battles, titanium dioxide, is a widely used white mineral powder found in products ranging from paint and sunscreen to toothpaste and food. Historically regarded as safe, the perception shifted in the early 2000s with the rise of nanotechnology. Research began to reveal that nanoscale titanium dioxide particles might interact with biological systems in ways that larger particles do not.
The pivotal moment for the safety assessment of titanium dioxide occurred in 2010, when the International Agency for Research on Cancer (IARC) classified it as “possibly carcinogenic to humans.” This classification was primarily based on animal studies showing that rats exposed to high concentrations of titanium dioxide particles developed more lung tumors. In response to this new classification, California added certain airborne titanium dioxide particles to its Proposition 65 list in 2011, mandating warning labels on affected products. Eight years later, the European Commission followed suit, requiring similar warnings on products sold in Europe.
Despite these warnings, significant scientific uncertainty remains. The debate over the carcinogenicity of titanium dioxide has sparked extensive discussions within the scientific community about the reliability of animal studies as predictors of human risk. While animal studies often suggest mechanisms of potential harm, translating these findings to human health poses considerable challenges.
Moreover, research on the toxicity of nano titanium dioxide particles has produced inconsistent results. Factors such as exposure levels and individual susceptibility contribute to varying conclusions about potential health risks. This ongoing ambiguity has created a fertile ground for legal challenges from industry groups, which argue that regulatory bodies have misinterpreted the scientific evidence.
The recent court rulings illustrate a shift in the legal landscape surrounding regulatory science. In both cases, the courts emphasized the importance of a rigorous evaluation of scientific data. The European court specifically noted that regulators had used an incorrect particle density value when assessing lung overload in rat studies, undermining their conclusions about human cancer risk. Consequently, it nullified the classification of titanium dioxide as a carcinogen.
Similarly, the US court acknowledged that while the warnings about titanium dioxide were literally accurate, they did not meet the legal standard of being “purely factual and uncontroversial.” The court highlighted the ongoing scientific debate surrounding the substance, leading to the conclusion that the warnings could mislead consumers.
These developments raise critical questions about the role of the judiciary in scientific matters. Critics argue that judges, lacking formal scientific training, should not override expert opinions from regulatory agencies. The challenge lies in balancing the need for regulatory caution with the courts’ responsibility to ensure that scientific evidence meets established legal standards.
As technologies evolve and more complex substances enter the market, the legal system faces the task of navigating scientific uncertainty. Regulators often operate under the premise of precaution, acting on potential risks even when definitive evidence may be elusive. This approach raises further questions: How can regulatory agencies justify action in the absence of clear proof? And how can scientists effectively communicate the uncertainty inherent in emerging fields?
The intersection of law and science is becoming increasingly prominent as new technologies and materials enter public use. The need for collaboration between scientific and legal experts is crucial in addressing these challenges. Ensuring that legal institutions are equipped to handle scientific complexity will be essential for protecting public health while upholding the integrity of scientific inquiry.
Rachael Wakefield-Rann and Sarah Wilson, both of whom have disclosed no financial affiliations that would benefit from this article, emphasize the importance of transparency and collaboration in navigating the complexities of science and law. As the dialogue between these fields evolves, it is clear that finding effective solutions to these challenges will require a concerted effort from all stakeholders involved.
