To avoid irritating the scalp and hair, wash it about four days prior to using a relaxer. Shampoo often contains ingredients that strip the hair and scalp of moisture and necessary oils.
In the event that shampooing up to four days before a relaxer is not possible, apply a bit of jojoba or castor oil to hair and scalp in order to provide some moisture. In addition to shampooing in advance of getting a relaxer, use a clarifying rinse, such as apple cider vinegar, or shampoo roughly a week before a relaxing treatment. This helps to keep hair from being weighed down.