Formaldehyde is a commonly used preservative and a known carcinogen. While it is not often added directly to beauty products, there are some ingredients that are used as preservatives in things like nail polish remover, body washes, and hair smoothing products that are known to release formaldehyde over time. The prime offenders you’ll see on ingredients labels are DMDM hydantoin, quaternium-15, diazolidinyl urea, imidazolidinyl urea, methenamine, and sodium hydroxymethylglycinate, and bronopol.
