This naturally occurring gas is a preservative in some hair products. Liquid versions are called methylene glycol and formalin.
Safety Status: Health Canada restricts the amounts that manufacturers can use, and it’s banned in aerosols because it’s carcinogenic when inhaled at high levels.
Smart Use: In 2011, Health Canada warned that some salon hair-straightening products (often called a keratin treatment) contain too much of formadehyde. Check with your salon if you get these treatments.