Washing your hair is probably the last place you would think worry about polluting the air. You wet your hair, put in the shampoo and work up a good lather, and then rinse it down the drain. It turns out that a chemical added to personal care products to make them feel smooth not only contributes to air pollution, but is detectable in amounts almost equal in size to car exhaust.
The Detective Work
Researchers in Colorado monitoring air quality kept getting a large signal every morning and couldn’t figure out what it was. Eventually a colleague recognized it as a compound called siloxane. The signal peaked every morning during the morning commute, so they assumed it was coming from car exhaust. The mystery deepened when they tested car exhaust and monitored roadside pollutants. They found nothing – no trace of the siloxane.
They then broke down the signal from the siloxane into hour by hour chunks and found that it peaked during the morning commute and then peaked again, albeit with a smaller signal in the evening, when people left work. They realized they were getting the signal after people used personal care products and went outside.
Why it Matters
Siloxane is added to lotions, deodorants, and shampoos to give a smoother texture to those products. It is considered non-toxic, but is a VOC (volatile organic compound) like components of car exhaust and many paint additives. These compounds are light, evaporate easily, and are easily released into the air. In the air when exposed to sunlight, these compounds form ozone and particulate matter. Ozone is the main component of smog and exposure to both can cause asthma or make asthma worse.
How can you tell if your personal care products contain siloxanes?
Check your product labels. The most commonly used siloxane is called polymethlysiloxane (PDMS). It is may also be called dimethicone, and sometimes dimethylpolysiloxane. In the US, all additives have to be listed on the label.
Safety of Siloxanes – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4884743/
Original Research this article is based on – https://pubs.acs.org/doi/10.1021/acs.est.8b00506