P10.138 Amino acids - improving hair fibre properties in cosmetic hair problems

C. Gummer, S. Shiel

The Procter & Gamble Company, Rusham Park Technical Centre, Egham, United Kingdom

Objectives: To understand the fundamental differences in amino acid composition of the hair shaft occurring during weathering. To develop a system to re-introduce amino acids lost by the hair shaft during weathering. To measure the benefits of re-introducing amino acids to the hair shaft.

Methods: Standard amino acid extraction/analysis techniques were first used to determine the difference in amino acid composition between root and tip ends of single hair fibres.  Armed with this knowledge, tensile and sensory testing of root and tip-end hair, was carried out to link the changes in amino acid composition to physical, tactile and visual properties.  Once a suitable amino acid system had been developed, deuterium labelling coupled with Scanning Focused Ion Beam Analysis was used to prove the penetration of the amino acids into the cortical region of the hair shaft.  Finally, tensile testing was used to demonstrate the benefits of the amino acid system under a variety of different application conditions.

Results: This research has clearly demonstrated that six specific amino acids are preferentially lost from the hair shaft during the weathering process; through a combination of mechanical, photochemical and chemical means.  The loss of the amino acid content can be ascribed to many of the common cosmetic hair problems.  Through deuterium labelling it is clearly evident that we can replace a combination of three of these lost amino acids directly into the hair shaft, where they are shown to provide significant tensile benefits to the hair shaft.

Conclusions: The amino acid composition of human hair undergoes a fundamental change during the weathering process, with six amino acids being preferentially lost from the hair. A combination of three of these lost amino acids has been demonstrated to penetrate into the hair cortex when applied under a variety of application conditions. Re-introduction of these three amino acids leads to a significant benefit in the tensile properties of the hair fibre, which in the long-term can lead to improvements in the aesthetic properties of the hair.