Very useful, I really like my hair now. It's smooth and shiny, looks much healthier after the procedure, no more damaged and dry ends. I recommend that you don't rinse the substance before using the hair straightener. To my mind the result is much better in case the keratin is removed several days after the hair is straightened and the procedure is over. In such condition you better not make pony tails before washing your hair the first time after the procedure. You may leave a row right on your hair which is not easy to be removed then.