Examining Bond-Building Hair Care Treatments

Introducing bond-building hair care products has created a new category for consumer purchase. These products include shampoos, instant conditioners, leave-in conditioners, and styling products. This article examines hair bonds and how they are strengthened with newly discovered chemical technologies.

What are the bonds in hair?

Hair is composed of 17 types of keratin. Eleven are acidic keratins with a pH around 5, while the other 6 are basic keratins with a neutral pH. The keratins have an α-helical structure and are held together via bonding. There are 3 types of bonds in the hair shaft, including hydrogen (water deformable bonds), ionic (salt bonds), and disulfide bonds. The disulfide bonds are the major strength of the hair shaft, arising from sulfur-containing amino acids, such as cysteine. These bonds are broken and reformed during chemical processing procedures to alter the shape of the hair shaft, such as permanent waving to make straight hair curly and permanent straightening to make curly/kinky hair straight. The disulfide bonds are also broken due to a process known as weathering, which is the sum of all physical and chemical trauma the hair suffers during grooming, shampooing, and exposure to wind/sunlight.

What is a bond-building hair care treatment?

Bond-building hair treatments increase the tensile strength of the hair shaft, making it more resistant to breakage during pulling and stretching from grooming or other trauma. The consumer term for this bond-building is reknitting, which is a colloquial term for restoring the disulfide, hydrogen, and ionic bonds.

How do bond-building hair care treatments work?

Disulfide bonds are broken during chemical processing, heat hair styling, and combing/brushing. When a disulfide bond is broken, 2 single sulfur hydrogen molecules are formed instead of 2 double sulfur hydrogen molecules. The single sulfur hydrogen molecule can combine with 3 oxygen molecules to create a new sulfate group that weakens the hair shaft. One bond-building product line contains bis-aminopropyl diglycol dimaleate that attempts to reform the disulfide bonds, thus strengthening the hair shaft. This chemical intercalates between the broken disulfide bonds and the dimaleate moiety protects the disulfide bonds to minimize breakage.

Another bond-building product uses 18-peptide technology to put amino acids back into the hair shaft. This technology was originally developed for rug fibers and has been adapted to hair care. Other bond-repairing products contain citric acid, maleic acid, lactic acid, or other acids, which lower the hair shaft pH, decreasing cuticle swelling to smooth the surface of the hair shaft, minimize friction, and prevent breakage during grooming. Some products contain hydrolyzed collagen proteins or silk proteins that can penetrate the hair shaft where cuticular scales are missing, thus minimally increasing the protein content of the hair by 5% to 8%. The proteins must be hydrolyzed, meaning broken into small pieces, in order to penetrate, but their presence in the hair shaft is short-lived as they diffuse in after application and diffuse out with water contact at the next shampooing. These temporary hair strengtheners must be reapplied with each shampooing. Bond-building shampoos and instant conditioners that are washed out of the hair are less effective than products left on the hair shaft, such as leave-in conditioners and styling products.

The last bond-building product line uses hydroxypropyl gluconamide, which is designed to penetrate the hair cortex and create new hydrogen and ionic bonds. It is sometimes combined with hydroxypropyl ammonium gluconate, a salt of gluconic acid that acts as a humectant to attract water to the damaged hair shaft. It, too, can increase hydrogen and ionic bonds in the hair shaft.

Summary

Many different technologies are employed in hair-bonding products, including reconnecting disulfide bonds, diffusing amino acids or patented peptides into the hair shaft, decreasing cuticular swelling, and restoring hydrogen and ionic hair bonds. None of these methods can recreate the strength of virgin, newly grown, unprocessed hair; however, this area of hair care has captivated consumers, and dermatologists will surely be asked about the effectiveness and value of these products.

Zoe Diana Draelos, MD, is a clinical faculty member in dermatology at Duke University School of Medicine in Durham, North Carolina, President of Dermatology Consulting Services in High Point, North Carolina, and Dermatology Times editor in chief emeritus.