The difference between a perm and a relaxer lies in the intended outcome and the procedure used to achieve it: a perm introduces curls and ringlets, but a relaxer is applied to eliminate natural waves and coils. However, the chemicals used in both treatments are similar and work to change the structure and texture of the hair. In fact, some smoothing systems employ a perm solution with a relaxer-style technique.
To achieve the desired hairstyle, the hair is manipulated into it after the chemicals in the perm or relaxer have started to break down the bonds in each hair's shaft. Thus, for traditional perms, the hair is combed and rolled onto plastic rods to create corkscrews. In a relaxer application, on the other hand, the hair is combed and smoothed to create a sleek look.
As each process results in a permanent change to the hair's structure that can only be removed by cutting it off, not all hair is healthy enough to safely undergo either treatment. Hair that has been bleached or colored with a permanent dye has already been compromised and may break heavily after a perm or relaxer. Additionally, hair that is dry or brittle may require extra deep conditioning before a stylist attempts either process.