Scientists Study Impact of Heat & Hair Styling Product Usage: ACS Article

Researchers studied emissions of volatile organic compounds (VOCs) in hair care products, including siloxanes. The scientists report in ACS’ Environmental Science & Technology that using these hair care products can change indoor air composition quickly, and common heat styling techniques — straightening and curling — increase VOC levels even more.

According to the report, some prior studies have examined the amounts of siloxanes released from personal care products, but most focused on those washed off the body, such as skin cleansers. They surmised these might behave differently from products that are left on the hair, like creams or oils. In addition, most previous studies on siloxane emissions haven't looked at the real-time, rapid changes in indoor air composition that might occur while people are actively styling hair, said the researchers.

Nusrat Jung, assistant professor in the Lyles School of Civil Engineering at Purdue University, and colleagues said they wanted look at VOCs released from hair products, especially in real-world scenarios such as small bathrooms where they’re typically applied.

The researchers set up a ventilated tiny house where participants used their usual hair products — including creams, sprays and oils — and heated tools. Before, during and after hair styling, the team measured real-time emissions of VOCs including cyclic volatile methyl siloxanes (cVMS), which are used in many hair care products. The mass spectrometry data showed rapid changes in the chemical composition of air in the house and revealed that cVMS accounted for most of the VOCs that were detected. Emissions were influenced by product type and hair length, as well as the type and temperature of the styling tool. Longer hair and higher temperatures released greater amounts of VOCs.

As a result of their findings, the researchers estimated that a person’s potential daily inhalation of one cVMS (decamethylcyclopentasiloxane, D5) could reach as much as 20 mg per day. In the experiments, turning on an exhaust fan removed most of the air pollutant from the room within 20 minutes after a hair care routine was completed, but the scientists note that this practice could affect outdoor air quality in densely populated cities. They say studies of the long-term human health impacts of siloxane exposure are urgently needed, because most findings are from animal studies.

On average, Jung’s team reports, a person can inhale a cumulative mass of 1-17 milligrams of potentially harmful chemicals in a single hair care session in their home.

Jung said the team “did not expect to see such significant emissions of volatile chemical mixtures from off-the-shelf hair care products during typical hair care routines that many people perform each and every day.”

“D5 siloxane has been found to lead to adverse effects on the respiratory tract, liver and nervous system of laboratory animals,” Jung said. “The use of the chemical in wash-off cosmetic products has already been restricted in the European Union because of this. Many of these products are scented, too, and some of the chemicals used to make these fragrances are potentially dangerous to inhale as well.”

According to the European Chemicals Agency, D5 siloxane is classified as “very persistent, very bioaccumulative.” And while the test results on laboratory animals is already concerning, Jung said, there is little information on its human impact.

“There has not been much in-depth research into this, so we really have no idea to what extent the threat these chemicals pose when inhaled over a long period of time,” Jung said. “There have been tests into ‘wash-off’ products like shampoos, but almost none for ‘leave-on’ products like hair gels, oils, creams, waxes and sprays.”

Jung’s research also noted that applying high heat to these chemicals, such as through curling irons and hair straighteners, serves to further release the chemicals into the air. When met with temperatures of 210°C, researchers found the chemical emissions from the hair care products increased anywhere from 50% to 310%.

Jung also said the chemical do not merely remain in a single room — or even a single home.

“Home ventilation is likely a major pathway of indoor-to-outdoor siloxane transport,” Jung said. “In urban environments, this is especially significant as you will have hundreds — even thousands — of homes ventilating out potentially harmful chemicals into the urban atmosphere all in a short span of time as people get ready for work and school in the morning. These chemicals are then collectively piped back into buildings through ventilation systems. So even if using products with harmful chemicals is not part of your hair care routine, you will still be impacted due to your surroundings in an urban environment.”

Surveys on different population groups indicate 16% to 70% of participants use leave-on hair care or hair styling products, Jung’s research reported. Considering an average use frequency of hair care products between two and five times a week, based on surveys on hair care product usage patterns, and assuming that 10% of leave-on hair care products are siloxane-based, the total indoor-to-outdoor emission of D5 could reach 0.4 to 6 metric tons a year in the US, according to researchers.

The authors recommend consumers run an exhaust fan to minimize the amount of chemicals inhaled, noted Purdue civil engineering PhD student and researcher Jinglin Jiang.

“Ventilation can be an effective way to reduce siloxane exposures during indoor hair care routines,” Jiang said. “Our model shows that turning on the bathroom exhaust fan can reduce D5 inhalation exposures by over 90%.”
Jung’s research reports that the cumulative indoor-to-outdoor D5 emission with the exhaust fan always off reaches 710 milligrams within three hours, while the indoor-to-outdoor D5 emission with the exhaust fan always on reaches 900 milligrams within only one hour.

Usage of Products

Jung’s experimental research was conducted in a residential architectural engineering laboratory that she designed: the Purdue zero Energy Design Guidance for Engineers (zEDGE) Tiny House—mechanically ventilated, single-zone residential building with a conditioned interior. A state-of-the-art proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) from Jung’s laboratory was used to measure D5 siloxanes and other volatile chemicals in the indoor air in real time, second-by-second.

The hair care routine emission experiments were conducted during a measurement campaign in zEDGE over a period of several months, including three experiment types: realistic hair care experiments that replicate actual hair care routines in the home environment, hot plate emission experiments that explore the relationship between the temperature of the hair care tools and volatile organic compound emissions, and surface area emission experiments that investigate how hair surface area impacts volatile organic compound emissions during hair care events.

For the realistic hair care routine emission experiments, participants were asked to bring their own hair care products and hair styling tools to replicate their routines in zEDGE. Prior to each experiment, the participants were instructed to separate their hair into four sections. The hair length of each participant was categorized as long hair (below the shoulder) or short hair (above the shoulder). The sequence of each experiment consisted of four periods, to replicate a real-life routine.

After hair styling, the participants had two minutes to collect the tools and leave zEDGE; this was followed by a 60-minute concentration decay period, in which zEDGE was unoccupied, and the high-resolution PTR-TOF-MS monitored the decay in indoor volatile organic compound concentrations. The experiments and subsequent analysis focused on indoor volatile organic compound concentrations and emissions during and after active hair care routine periods.

This research was funded and supported by Purdue University, the Alfred P. Sloan Foundation, and the National Science Foundation. Jung’s team plans to investigate the many other chemicals detected in these experiments that were not reported in this study.

Additional Reading

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