MONDAY, Dec. 6, 2004 (HealthDayNews) -- Experiments with the brain cells of rats show that contact with an ingredient found in shampoos, hand lotions and paint causes neurons to die.

The chemical, methylisothiazolinone (MIT), belongs to a class of compounds called biocides. These are used in the manufacture of many common household products and industrial water cooling systems to prevent bacteria from developing.

According to the National Institutes of Health, brands containing MIT include the shampoos Head and Shoulders, Suave, and Clairol, as well as Pantene hair conditioner and Revlon hair color.

"As far as I can tell, no neurodevelopmental testing has been done on MIT," said lead researcher Elias Aizenman, a professor of neurobiology at the University of Pittsburgh School of Medicine.

Aizenman said he is concerned that without such testing it is not known if, for example, a pregnant woman who is exposed to MIT could put her fetus at risk for abnormal brain development. People working directly with MIT are those most at risk, he said.

In earlier experiments with rat brain cells, Aizenman's team found that direct exposure to MIT in concentrations like those found in hand cream was enough to kill neurons. In the current series of experiments, also with rat cells, the researchers found that a long exposure to low concentrations of MIT caused a malfunction in the ways neurons communicate with each other.

"One of the things that this compound was very good at was preventing neurons from communicating with other neurons," he said.

Aizenman presented his findings Dec. 5 at the American Society for Cell Biology annual meeting in Washington, D.C.

Whether long-term exposure to products containing MIT is dangerous is not known, Aizenman said. "Can I say that these products are safe to use? No," he said. "Can I say that these products are unsafe to use? No."

Aizenman believes that testing needs to be done to determine if MIT is harmful to humans in the concentrations found in household products.

"It appears that the Environmental Protection Agency [EPA] does not require neurodevelopmental testing," Aizenman said. "That is bothersome. Maybe there are substances that have made it into general use that could be damaging to the nervous system. Regulators need to take a hard look this and require more tests."

The work that Aizenman has been doing "is important in understanding the things that people are exposed to on a chronic, daily basis," said Beth Ann McLaughlin, an assistant professor of pharmacology at Vanderbilt University.

McLaughlin added that people using products containing MIT should be skeptical. "There is a healthy dose of skepticism that needs to come when using any products or being intensely exposed to any compound," she said.

"These findings are expected," said Gerald McEwen, vice president for science at the Cosmetic, Toiletry and Fragrance Association. "MIT is a biocide. The purpose of it is to kill bacteria. You would expect it to be detrimental to any type of cells."

McEwen said that direct exposure to high concentrations of MIT will be irritating to the skin, because it can damage skin cells. However, he doesn't believe that MIT poses any dangers to consumers in the low concentrations found in household products.

"The ability of MIT to cause neurotoxicity has been studied," McEwen said. In animals exposed to MIT, there has been no hint of neuro-damage, because MIT affects only the cells it touches and there is no way for it to get into the bloodstream and go to the brain, he said.

"It can't get to your brain cells, period," he emphasized.

MIT has been approved as a biocide by the EPA, which looked at the neurological effects, McEwen added. This information was published by the Cosmetic Ingredient Review, an industry program that reviews the safety of cosmetic ingredients, he explained.

However, McLaughlin remains concerned. "The quantity of compounds that we can make that make the quality of life wonderful, in the short term, is growing," she said. "But we are lagging in our understanding of what those compounds can do to our health and our children's health."

More information

The National Institutes of Health has a list of household products containing MIT.

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