It has all the makings of a toxic controversy. Growing evidence suggests that the molecules known as forever chemicals — used in everyday items like cosmetics, non-stick pans and water-repellent clothing — can build up in the environment and in the body, to the detriment of both.

Last year, the world’s pre-eminent chemistry organisation announced a panel would look again at how the chemicals — more properly known as per- and polyfluoroalkyl substances, or PFAS — are defined. That has stoked unhappiness among some researchers, who suspect that the rethink, to be carried out by the International Union of Pure and Applied Chemistry, might end up narrowing the definition and letting some forever chemicals off the regulatory hook. The current definition, they protest, is grounded in science and works well; the new initiative, they argue, is motivated by political or economic considerations, rather than science.

Their objections deserve a hearing. In setting out its reasons for redefining a class of chemicals that have existed for decades, the chemistry union tellingly mentions European regulation and declares it is “hardly feasible” for around 9,000 PFAS to face a possible ban from 2026. That seems an odd statement: it is unclear why a chemically rigorous definition of a chemical, as newly drafted by the world’s top chemistry body, should nod to anything other than chemistry.