- Older lye products of the past have been replaced with a new wave of products and treatments that contain certain acids that help in the hair straightening process. A liquid solution is used in most of these processes and applied to the scalp of the person's hair that is to be straightened. The solution seeps into the hair shaft, where it begins to create the reaction process needed to straighten hair. In some treatments, like the recently Asian-introduced thermal reconditioning, heat is applied to the hair during this process to help the chemical reaction needed to restructure the hair. Allowing the acidic solution to sit lets it get deep into the hair shaft and results in a restructuring of bonds.
- The premise behind using acids to straighten hair is based around the structure of hair and altering this subtly for a desired result. Certain bonds in hair must be altered in order to change hair structure, and these bonds are responsible for holding strands in a matrix or attaching keratin strands that are separated. These bonds, the most popular known as disulfide bonds or cystine bridges, are what make up the natural appearance of hair, whether curly, straight, kinky, or wavy. Since disulfide bonds are found mostly in the outer cuticle of a shaft known as the epicuticle, acids can penetrate these easily to break down and reorganize the hair structure.
- Acids used in the hair straightening process can vary from product to product, the most commonly used being thioglycolic. The acids that are applied to the scalp serve to denature the hair for a short amount of time. Denaturing the hair is when proteins inside the inner hair follicle roam past each other because the disulfide bonds are broken. Cystine proteins contain sulfur that helps in the bonding process and this is what is broken down in order to allow metamorphosis of the hair. Acids help to reduce and sever these bonds, which allow a person to either pull the hair straight, or use approved appliances to do the same. After about a 30-minute period, the hair begins a process called oxidation, where new bonds are created inside the hair. Upon the oxidation process, the new cystine bonds keep the shaped hair's new structure, hardening in place. This leaves hair straight for longer intervals, amounting to months depending on natural hair type, although new growth must be treated upon appearance.
