8. Keratin Straightening

The Brazilian blowout seemed like a dream come true for girls with persistent frizz — an in-salon treatment that gave you semi-permanent results of smooth, shiny strands — but that dream quickly became a nightmare with the news that many of these treatments contained unsafe levels of formaldehyde. Long-term exposure to formaldehyde has been linked to cancer, not to mention side effects of eye and nervous system disorders, respiratory tract problems, chest pain, vomiting, and rashes.

This treatment is particularly dangerous for salon technicians and people who undergo frequent straightening treatments because they are constantly exposed to the chemicals. "The Cosmetic Ingredient Review (CIR) Expert Panel recently completed a comprehensive review and found that the safety of methylene glycol and formaldehyde in hair straightening products depends on a number of factors, including the concentration of formaldehyde and methylene glycol, the amount of product applied, the temperature used during the application process, and the ventilation provided at the point of use," says Jay Ansell, PhD,  vice president for cosmetics programs at the Personal Care Products Council. "The Panel concluded that under present practices of use and concentration, formaldehyde and methylene glycol are unsafe in hair straightening products. Consumers should go to a licensed professional salon and ensure that adequate safety measures and ventilation are present." If your salon says that they use a formaldehyde-free straightener, make sure they have the proof to back that up.