Methylisothiazolinone (MIT) is becoming increasingly popular as a preservative to replace parabens. Even some products claiming to be certified organic use this preservative, as certain percentages of non-organic material is allowed by the USDA.

In lab studies, the bacteria-killing agent was shown to restrict the growth of immature rat nerve cells. Studies on live animals are still needed to confirm the findings. Researchers say the early test tube evidence suggests that prolonged exposure to MIT, or exposure to the chemical at high concentrations, could damage the nervous system.

“The biggest potential concern, says lead researcher Elias Aizenman, PhD, of the University of Pittsburgh School of Medicine, is for the fetuses of pregnant women exposed to high doses of MIT.”

Read more about MIT in the CBS article Shampoo Preservative Concerns.