Check that label!: Methylisothiazolinone

Found in many conditioners and shampoos, methylisothiazolinone (MIT) is commonly used as a preservative to inhibit microbial growth.

Published in the Journal of Neuroscience in September of 2002 was one of the first studies into the safety of MIT. Although it has been used in personal care products for many years, there was inadequate information regarding its safety, leading a group of researchers at the University of Pittsburgh School of Medicine to conduct a study of it.

There is increasing evidence supporting that environmental exposure to neurotoxic substances may lead to the development of neurodegenerative diseases, such as Parkinson's and Alzheimer's.

In the study, the researchers isolated rat cortical neurons and applied 100 micromolar MIT for only 10 minutes. Within 24 hours, the neurons underwent widespread cell death. They found that the reaction cascade caused by exposure to MIT resulted in the depletion of glutathione, a powerful endogenous antioxidant, and production of reactive oxygen species, which are free-radicals contributing to DNA damage.

Smaller doses of MIT administered over a long period of time also showed neurotoxic properties. While the smaller doses did not outright kill neurons, it did inhibit the growth of neurites, which are used to form connections between neurons, essential for different parts of your brain to be able to communicate with each other. This has some pretty obvious health implications for adults, but even more so for developing fetuses who may become exposed through the mother's toxicity.

While we're at it, I should probably mention parabens too, which are also preservatives, are known to be toxic and are probably more ubiquitous than MIT. Parabens have the ability to mimic estrogen and because they are easily absorbed into the skin and are lipophilic, they may accumulate in the body. Studies have shown them to be particularly concentrated in breast tissue, and have found them to induce the growth of cancerous breast tissue.

I ventured over to the local drugstore to pick up a few things and couldn't help peruse the hair and skincare aisles to do some label checking. Although I didn't track specific numbers, I estimate that well over 50% of the labels I checked contained MIT, and probably closer to 90-95% of things I looked at contained at least one paraben.

So what does all this mean for you? Although you should bear in mind that all of this data is not yet conclusive, an increasing amount of evidence does support that these compounds may very well not be safe for use. In the end, I think that knowledge is power; as long as consumers are well-informed about the potential safety concerns of the things they use in their everyday lives, then each individual person is free to decide whether they feel the risk is worth taking.

Sources:
In Vitro Neurotoxicity of Methylisothiazolinone, a Commonly Used Industrial and Household Biocide, Proceeds via a Zinc and Extracellular Signal-Regulated Kinase Mitogen-Activated Protein Kinase-Dependent Pathway

Toxic Effects of the Easily Avoidable Phthalates and Parabens