The US Department of Labor's Occupational Safety and Health Administration (OSHA) is warning hair salon owners and workers about the potential dangers of formaldehyde exposure from working with some hair-smoothing and hair-straightening products (http://www.osha.gov/SLTC/formaldehyde/hazard_alert.html).
OSHA officials found formaldehyde in the air when stylists used certain hair-smoothing products, some of which do not have formaldehyde listed on their labels or in material safety data sheets, which is required by law.
Hampton T. Toxic Hair Products. JAMA. 2011;305(20):2056. doi:10.1001/jama.2011.683