A preservative commonly found in cosmetics such as shampoo and moisturizers harms developing nerve cells, according to a controversial study.

But claims that the compound may therefore pose a risk to unborn babies have provoked concern from other scientists, who are worried that such assertions may create unnecessary panic.

Methylisothiazolinone (MIT) is widely used in hand creams, shampoos and other cosmetics. It kills bacteria, making it easier to store the lotions for longer periods of time without colonies of microbes developing.

Safety tests have previously found that the chemical may cause slight skin irritation in susceptible people1. But Elias Aizenman, a neurobiologist at the University of Pittsburgh, Pennsylvania, says that he could not find any information about the chemical’s impact on developing nerve cells.

So his research team has been studying how the chemical affects neurons taken from the brains of rat embryos. Preliminary research published in 2002 found that relatively large doses of MIT killed most of the neurons within ten minutes2. Many chemicals are toxic in high enough doses, however, so Aizenman’s group went on to test much lower doses over longer periods of time. This mimics the occupational exposure of people who work with MIT every day, for example in factories that make cosmetic products.

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