It all depends on the straightener quality and also how you take care of your hair. Your hair should be conditioned enough which will give you a good result also please use heat protection spray this really protects the hair damage. I have been using GHD straightener for years and no issues at all. Permanent straightening has it's own pros and cons, I have recently done and went through lots of hair fall though I had done the procedure in a reputed salon. It depends how your body reacts with those chemicals.