Why do you have to wait 2 days to wash your hair after a perm?

Getting your hair wet after a perm can de-activate the curls. The chemicals used to curl the hair and keep it curly do not hold up when exposed to water. After a day or so, the chemicals have done their work fully on the hair and are no longer succeptible to water damage. After a perm the hair is soft and the cuticle is still open. If you wash your hair the water and shampoo will get into the hair shaft and undo all the work your stylist did and you will have wasted your money.