Formaldehyde-free hair-straightening products have gained popularity as a potentially safer option than their formaldehyde-containing counterparts — but a new series of medical cases calls the safety of these alternative products into question.
Formaldehyde — as well as liquid forms of the chemical, called formalin and methylene glycol — is added to hair-straightening and hair-smoothening products as a preservative to extend shelf life and to help lock the hair's texture in place for a long time.
