A proposal to ban formaldehyde in hair-straightening products that was scheduled to take place in April has not been released by the Food and Drug Administration, disregarding the agency’s own deadline.

The proposal had come after wide-ranging studies found an association between some of the ingredients in hair-smoothing and hair-straightening products, which are used mostly by Black women, and cancer.

It is unclear why the FDA has not released its proposed ban. The agency has not responded to requests for comment by NBC News.

In 2022, a decadeslong study by the National Institutes of Health of more than 33,000 Black women showed an increase in uterine cancer among those who regularly used hair relaxers.

Several women who had uterine cancer or other severe illnesses joined class-action lawsuits against major beauty product manufacturers, including L’Oreal and Revlon. Thousands of women allege that the hair products’ ingredients caused them to develop uterine cancer or other severe health problems.