It has become a popular belief that a woman’s hair should be dirty before she applies relaxer to it. It is believed that relaxing dirty hair doesn’t hurt and the time of relaxing the hair can be extended since there is no pain.
This has led to many women leaving their hair unwashed for weeks or months because they want to relax it. Well, that myth is so false. Hair does not have to be dirty before hair relaxers are applied.
On the contrary, your hair should be washed at least four days before the day scheduled for the hair relaxer to be applied, because shampooing will remove some of the necessary oils and natural lubricants of your hair, which is supposed to protect it during the chemical(relaxer) application process.
So after four days, your hair would have produced sufficient natural lubricants(serum) to protect it when it is relaxed. You can also add some castor, olive, jojoba or coconut oil to the hair and scalp to protect it as well.
Nonetheless, if you wash your hair on the day you want to apply a relaxer, then you will most likely have burns and pain, because your hair would not have produced enough natural lubricants to withstand the relaxer.