Health Hazards of Hair Straightening

Photo: A stylist uses a flat iron to straighten hair. A stylist uses a flat iron to straighten hair.

Formaldehyde levels during hair straightening treatments can exceed federal Occupational Safety and Health Administration (OSHA) short-term exposure limits and the National Institute of Occupational Safety and Health (NIOSH) recommended ceiling, finds a study published in the Journal of Occupational and Environmental Hygiene.

Hair straightening products are available at over 6,000 salons in the United States, according to a team of authors led by UC Berkeley alumna Michelle Stewart, MPH’11. “Although some salons have switched to products labeled as formaldehyde-free, our study suggests a significant number of salon workers and customers may be unknowingly exposed to formaldehyde levels that fail to meet federal limits of safety,” says Stewart.

“If you were to look at the product we sampled, you would see a warning label and the Material Safety Data Sheet would indicate formaldehyde as an ingredient. One of my concerns in its use is that most salons and stylists who use the product are not equipped with the resources, such as localized exhaust ventilation, to properly mitigate the exposure to their clients and themselves,” notes Stewart. “If it’s not feasible to establish adequate engineering controls, I would emphasize the use of products that have been tested by a third party to have minimal levels of formaldehyde in the solution.”

Formaldehyde, classified as a known human carcinogen by the International Agency for Research on Cancer, can also trigger short-term exposure symptoms. Watery eyes, irritations of the nose and throat, coughing, nausea, and skin irritation are the most common. Previous studies have also associated formaldehyde exposure with asthma and reproductive harm, the authors add.

For the paper, scientists simulated the use of hair straightening products containing methylene glycol, a hydrated from of formaldehyde, in a controlled air chamber. Wearing fit-tested air purifying masks, they performed typical hair straightening procedures on a wigged mannequin. One fluid ounce of product was applied to the hair before it was blow-dried and straightened with a flat-iron.

Air samples taken during the simulations showed the stylist’s breathing exposure to formaldehyde was highest during blow-drying, up to 3.1 parts per million (ppm). The second highest exposure, 2.4 ppm, occurred during flat-ironing. OSHA’s short-term exposure limit to formaldehyde is 2 ppm while NIOSH’s recommended ceiling limit is 0.1 ppm.

“This study confirmed previous monitoring results reported by others, namely, formaldehyde exposures can exceed permissible limits when using some hair straightening products,” reports Mark Nicas, adjunct professor, Environmental Health Sciences, UC Berkeley School of Public Health. “The novel aspect here is that using a controlled test chamber allowed quantifying the formaldehyde mass emitted during the procedure. Given this value and some ventilation information, one can reasonably predict a stylist’s formaldehyde exposure by applying a mathematical model.”

The study, funded by NIOSH and COEH, recommends the use of hair straightening products containing formaldehyde less than 1 milligram per milliliter to maintain exposure levels within OSHA and NIOSH limits.

Co-authors from the UC Berkeley School of Public Health include alumni Trevor Bausman and Mark Nicas, as well as Kazukiyo Kumagai from the Division of Environmental and Occupational Disease Control at the California Department of Public Health.

Read the journal article.

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