Beauty experts recommend not using shampoo or conditioner on the hair for at least 48 hours after getting a perm, though some specially prepared shampoos can be used after 24 hours. The consensus is that shampooing too soon affects the hair's pH balance, which in turn affects the perm.
During the perm, the hair stylist uses special products to keep the hair soft and moisturized. Shampooing causes the hair to lose moisture, which is a good reason not to shampoo chemically treated hair too soon.
"Perm" is short for "permanent" or "permanent wave." Evolved from earlier thermal methods that began in the 19th century, modern perms take roughly 15 to 30 minutes and rely primarily on chemicals to change the hair's pH.