Replenishing Amino Acids in Damaged Hair
Beth Huggins, Ph.D1; Chris Gummer Ph.D2; Cheri McMaster MS1; Emily Pack BS 1 ;
1The Procter & Gamble Company, Sharon Woods Technical Center, Cincinnati, OH; 2The Procter & Gamble Company, Rusham Park Technical Center, Egham, Surrey, UK
As the main building blocks of hair, the loss of amino acids not only directly affects the structure of the hair shaft, but also it's overall appearance and behavior1. Many investigators have analyzed the specific amino acid content2 and more recent studies have indicated that significant quantities of certain amino acids are depleted from the hair during the weathering process, as a result of mechanical, photochemical and chemical damage3. A vital step in helping combat cosmetic hair problems is to understand amino acid loss and methods for reintroducing amino acids into the hair shaft.
To understand fundamental differences in the amino acid composition as a result of the weathering process. To develop a system to reintroduce amino acids lost by the hair shaft during weathering. To demonstrate and quantify the relative penetration/replenishment of amino acids lysine, histidine, and tyrosine (as methyl tyrosinate HCl)
Amino Acid Analysis
Samples of hair from different Caucasian female subjects (n=10, average length >20 cm), were used for this analysis. Amino acid quantification was carried out on root and tip portions via acid hydrolysis in HCL, followed by individual component determinations from an automated acid analyser.4 Root to tip differences (%) for each amino acid were determined within the same fiber (to remove fiber-to-fiber variation).
Amino Acid Penetration
An ‘active blend' of three of the specific amino acids lost from hair during weathering, was prepared from histidine, tyrosine methyl ester, and deuterated lysine (HTL complex). Mid brown, single head, virgin European hair was treated with this active blend, delivered from a range of formulation chasses, using a standard experimental protocol.5 The penetration of the amino acids was subsequently measured using a Scanning Focused Ion Beam Nuclear Reaction Analysis methodology reported in the literature.6
Amino Acid Replenishment
The HTL amino acids were labeled with deuterium and incorporated into commercial formulations of shampoo, conditioner and conditioner treatments. Note: only nonexchangeable hydrogen atoms were labeled with deuterium. Single lot hair swatches were treated following P&G standard protocol, which includes a warm water rinse. After treatment, hair was equilibrated in a controlled temperature/humidity room for 24 hours. The hair was then cryopulverized. Finally, the pulverized hair was sampled (~100-500 micrograms) and analyzed via Thermal Conversion Elemental Analysis Isotope Ratio Mass Spectrometry, TC/EA IRMS, at Isotech Labs, Champaign, IL. To account for natural deuterium in the hair, reported values are deltas vs. control (water treatment). There was a control for each hair type (Caucasian Mod. Damage and African relaxed).
Amino Acid Analysis - Root to Tip Differences
It was determined that a small number of specific amino acids are preferentially lost from the hair during the weathering process (table opposite); specifically, Lysine, Histidine, Tyrosine, Cystine, Methionine and Tryptophan. Of these amino acids, Lysine, Histidine and Tyrosine were found to be suitable for and stable in cosmetic formulations, and were used in subsequent experiments.
Amino Acid Penetration - The Nuclear Reaction Analysis
Deuterium map for virgin hair treated with amino acid complex (delivered from shampoo) is shown above right. It is clearly evident that the amino acid complex has penetrated into the cortex of the hair.
Amino Acid Replenishment - Replenishment was demonstrated across all formulations and hair types tested. The amount of amino acids detected increased significantly with each product added to the treatment regimen (chart below). Further, by increasing usage (cycles), relative amino acid replenishment increased (chart above right).
(Insert six charts here)
This study has shown that it is possible to use known analytical techniques to gain a new understanding of the subtle differences occurring in the composition of hair throughout the weathering process. We have shown that the composition of human hair undergoes a fundamental change as a result of this process. More importantly, this study has allowed us, for the first time, to identify those specific amino acids that are preferentially lost from hair during weathering. From this platform understanding, we developed a complex of three of the lost amino acids, capable of being delivered from a range of cosmetic chasses. Using advanced analytical techniques, we have been able to prove that this amino acid system is capable of penetrating right into the cortex of the hair. It is also clear that the relative concentration of amino acids delivered to the hair shaft is a function of fiber damage level, the number of product treatment cycles and multiple delivery systems used in combination.
References1. ‘The hair shaft - aesthetics, disease and damage', J Gray, R Dawber, D Whiting (Eds), Royal Society of Medicine Press Limited, 1997. 2. ‘Amino Acid Composition of Human Hair', CR Robbins and CH Kelly, Textile Research Journal, October 1970, 891-896. 3. "Amino Acids- A Potential Solution to Cosmetic Hair Problem', Intercontinental Meeting of Hair Research Societies, Journal of the German Society of Dermatology, Band 2 (6) 2004, 551. 4. To note tryptophan cannot be measured using this technique. Determination of tryptophan levels was carried out using a specialist colourimetric method. 5. ‘The Penetration of Deuterium Labeled Amino Acids into the Hair Delivered from Wash-Off and Leave On Formulations', P Meredith, P&G Technical Report BG-00-31. 6. PM Jenneson, AS Clough, JL Keddie, JR Lu and P Meredith, Nuc. Instrumt. Meth. Phys. Res. B, 132, 697.