hair can fall out or be damaged if you leave the stuff on too long or it's too strong for your hair.

right, the hair that grows afterwards will be back to it's natural state, and if you don't know how to take care of your hair once it's in that state, it could potentially fall out or get extremely damaged. If your hair is currently rough or curly even, in smoothing it either with heat or chemically, you're breaking up the hair's natural bonds and reconstructing it, to be "smooth or straight". So you can't necessarily treat the hair the same as it would before the smoothing treatment. However, everyone's different, and everyone has different levels of keratin vs moisture in their hair which makes it difficult to say what the exact side effects may be.

No.. Once your hair stars growing it'll go back to it's natural state.just the hair that gets permed will be the smooth part.the only side effect I know of is your hair falling out.