Bathroom chemistry

Is your family shampoo potentially harmful? Let’s begin by considering the three compounds mentioned previously. These were methylisothiazoline, dimethicone, and the grouping generally described as parabens.

Methylisothiazoline is sometimes included in shampoo and personal hygiene products to limit the potential for microbial contamination in water based solutions. Like many artificial preservatives, methylisothiazoline appears to disrupt the biological integrity of experimental animal subjects. The most alarming of these was the finding that prenatal exposure in laboratory rats resulted in disorientation and destruction of immature nerve cells. This research raised the possibility that the neural development of unborn human babies might also be disrupted (Du, et al; 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, Journal of Neuroscience 22:7408-7416; 2002).

Dimethicone has been included in some shampoo and hygiene products as an emulsifier, enabling the combination of water and oil based compounds. It is a silicon based compound which not only coats the surface of hair, but also the skin, restricting normal respiration.

Parabens are another class of preservative compounds which protect against microbial contamination. They are now associated with a body of evidence indicating their potential to disrupt estrogen reception. A recent study detected traces of parabens in the tissue samples removed from a group of breast cancer patients (Darbre, et al; Concentrations of parabens in human breast tumors, Journal of Applied Toxicology 24: 5-13, 2004). While there is insufficient evidence at present to conclude any causal links between paraben exposure and breast cancer, several health agencies have revised their guidelines for safe exposure.

When considering the rationale of manufacturers who use potentially harmful ingredients, it’s important to appreciate the range of alternative options which currently exist. Despite the additional expense and technical difficulties, it remains feasible to produce high quality shampoos and other hygiene products using only natural and organically certified ingredients. From an ethical and consumer focused perspective, these minor barriers must be offset against the long-term benefits.