Many hair care products contain siloxanes – a broad class of silicone-based compounds – that can become airborne during hair drying and styling. Evidence suggests siloxanes persist in the environment and cause liver or lung damage in rodents. A recent study found that a person can inhale up to 17 milligrams of siloxanes in a single home haircare session.

Researchers conducted multiple experiments that replicated typical home haircare sessions using hair dryers, styling equipment, and products. Then, they measured the amount of chemicals emitted during the sessions using mass spectrometry.

They found that the number of airborne chemicals emitted during haircare sessions, including monoterpenes, monoterpenoids, and propylene glycol, increased considerably indoors, especially when the various haircare products were heated. The most abundant chemical was a siloxane compound called D5, with participants inhaling up to 17 milligrams of siloxane in a single session.

Using an exhaust fan reduced the amount of inhalable D5 by roughly half; however, the quantities of the exhausted compound increased outdoors. The researchers estimated that the emission of D5 from indoor to outdoor environments in the U.S. could be as high as six metric tons yearly.

These findings suggest that people who use widely available haircare products in indoor environments are exposed to large quantities of inhalable, harmful compounds. These compounds can then be transmitted to the outdoor environment, where they persist, potentially posing considerable health threats.

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