Back in 2007 they used to use formaldehyde in the Brazilian Keratin treatment and there were the problems like KyCurly mentioned below. But it's all changed now and there is NO formadelhyde in the product. My friend had it done by Michelle Mascari and she LOVES it! Go to http://brazilianblowoutinhouston.com if you live in the Houston area, ask Michelle for a consultation. The website answers all your questions. You can still wear curls in your hair too if you want. It just takes out all of the FRIZZ. Hope that helps.