I have a lot of hair, frizzy, quite dry, that has undergone dyeing and highlights. The hair straightened better than any keratin treatment I have done, but the truth is that it dried them out quite a bit. Some strands with highlights got burned and some (very few) were completely cut off. Nevertheless, after applying a good cream afterwards, I can say that the result is what I wanted and expected. It couldn't straighten the hair so much and not damage it at all. It smells like a perm, not pleasant at all, but it is not a strong smell and mainly it does not burn the eyes and nose like the formaldehyde contained in keratin treatments (even those that are supposed to be formaldehyde-free). One needs to also get the neutralizer and the post perm treatment, and it is a whole process, but I was really impressed by how straight they became and how quickly (as far as this specific product that goes first is concerned, because with all the things you have to apply afterwards, you want it to be a two-hour process).