The combination of common hair care products and the heat of styling appliances can produce levels of nanoparticle air pollution on a par with standing by a busy road, a new study reveals.
Particles up to 500 nanometers in size – around 200 times smaller than the width of a human hair – are created in the process, which are fine enough to get deep into the lungs. These findings raise serious questions about the health hazards we might be exposing ourselves to with everyday hair care routines.
The study was carried out by a team from Purdue University in the US, using a purpose-built tiny house lab. The lab has previously been used to examine chemicals released by hair care products, but here the researchers wanted to take a closer look at the associated air pollution.
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"This is really quite concerning," says civil engineer Nusrat Jung. "The number of nanoparticles inhaled from using typical, store-bought hair care products was far greater than we ever anticipated."
"Studies of this kind have not been done before, so until now, the public has had little understanding of the potential health risks posed by their everyday hair care routines."
The researchers enlisted the help of seven volunteers who went through 21 hair care routines in total, covering five different products and appliances such as straighteners, curlers, and wavers. Nanoparticle air pollution was then measured in each case.
Routines lasting 10 to 20 minutes could produce more than 100,000 nanoparticles per cubic centimeter, the experiments showed. Simulation models showed these concentrations could allow more than 10 billion nanoparticles to be inhaled, with many finding their way into the deepest parts of the lungs.
Heating the hair care materials to more than 300 ° F (149 °C) was key to distributing substantially more nanoparticles through the air. At cooler temperatures, far fewer nanoparticles were created, and those that were produced generally remained in the hair.
"Atmospheric nanoparticle formation was especially responsive to these heat applications," says civil engineer Jianghui Liu.
"Heat is the main driver – cyclic siloxanes and other low-volatility ingredients volatilize, nucleate and grow into new nanoparticles, most of them smaller than 100 nanometers."
The damage caused by these particular nanoparticles isn't clear, though research into the health effects of micrometer-sized particles is increasingly showing the risks associated with air pollution in general.
As they are so small, nanoparticles – and any health impacts they cause – are difficult to trace. That said, animal studies have shown how nanoparticles in the lungs can increase inflammation and other types of tissue damage.
The advice from the researchers is to make sure any areas are as ventilated as possible when using hair products with high levels of heat. They also recommend conducting further experiments to track nanoparticle pollution in more detail and to better understand the chemical composition of these floating specks.
"By addressing these research gaps, future studies can provide a more holistic understanding of the emissions and exposures associated with heat-based hair styling, contributing to improved indoor air pollution assessments and mitigation strategies," says Jung.
The research has been published in Environmental Science & Technology.