What procedure enhances the curl or wave in natural hair?

The procedure that enhances the curl or wave in natural hair is a permanent wave. This technique involves the use of chemical solutions and heat to alter the structure of the hair, allowing it to hold a new shape—typically creating curls or waves that can last for several months. Permanent waves are designed to provide long-lasting results, making them a popular choice for individuals looking to add volume and texture to their hair.

The process works by breaking and reforming the disulfide bonds in the hair. By wrapping the hair around perm rods and applying a chemical solution, the hair is set into a curled position. After the appropriate processing time, a neutralizer is applied to lock in the new shape. This distinguishes a permanent wave from other treatments that do not fundamentally change the hair's structure or provide a lasting curl.

In contrast, the other options on the list do not enhance curls or waves in the same manner. Deep conditioning treatments primarily focus on moisturizing and restoring the hair's health, flat iron treatments straighten the hair, and blowouts focus on smoothing and volumizing styled hair without introducing curls.