During the styling process, particles up to 500 nanometers in size are formed—about 200 times smaller than the width of a human hair—and small enough to reach deep into the lungs. These findings raise serious questions about the health risks we may expose ourselves to during daily hair care routines.

The study was conducted by a team from Purdue University in the United States, using a specially designed small home laboratory. This lab had previously been used to examine chemicals emitted from hair care products, but this time researchers wanted to closely examine the related air pollution.

Civil engineer Nursat Jang said, “This is really concerning. The number of nanoparticles inhaled from using typical store-bought hair products was much higher than we expected.”

She added, “Studies of this kind have not been conducted before, so until now, the public had a limited understanding of the potential health risks posed by daily hair care routines.”

The researchers enlisted seven volunteers who underwent a total of 21 hair care routines, involving five different products and devices such as flat irons, rollers, and curling tools. Nanoparticle air pollution was measured in each case.

The experiments showed that routines lasting 10 to 20 minutes could produce more than 100,000 nanoparticles per cubic centimeter. Simulation models indicated these concentrations could allow inhalation of over 10 billion nanoparticles, many reaching the deepest parts of the lungs.

Heating hair care materials above 300 degrees Fahrenheit (149 degrees Celsius) was a key factor in releasing more nanoparticles into the air. At lower temperatures, far fewer nanoparticles were produced, and those produced generally remained in the hair.

Civil engineer Jianghui Liu explained, “Nanoparticle formation in the atmosphere was particularly sensitive to these heat applications. Heat is the main driver—cyclic siloxanes and other low-volatility components evaporate, then cluster and grow into new nanoparticles, most smaller than 100 nanometers.”

It is unclear what specific harm these nanoparticles cause, although research on the health effects of micrometer-sized particles increasingly shows risks associated with air pollution in general.

Due to their small size, nanoparticles are difficult to track along with any health effects they cause. However, animal studies have shown how nanoparticles in the lungs can increase inflammation and other types of tissue damage.

Researchers recommend good ventilation in any areas where hair products are used at high temperatures. They also call for further experiments to track nanoparticle pollution in more detail and better understand the chemical composition of these airborne particles.

The researchers conclude, “By addressing these research gaps, future studies can provide a more comprehensive understanding of emissions and exposures related to heat-based hair styling, contributing to improved indoor air pollution assessments and mitigation strategies.”

The study was published in the journal Environmental Science & Technology.