]. Cosmet. Sci., 58, 347-357 Quly/August 2007) Hair and amino acids: The interactions and the effects EIKO OSHIMURA, HIROSHI ABE, and RINA OOTA, AminoScience Laboratory, Ajinomoto Co., Inc., Suzuki-cha 1-1, Kawasaki 210-8681, Japan. Synopsis The interaction and the function of some amino acids in hair care applications are discussed. When amino acids are applied to hair in the form of simple aqueous solution, uptake of the amino acids is mainly controlled by ionic equilibrium. When amino acids were incorporated in a hair conditioner, the result was quite different, suggesting the importance of interaction between the amino acids and the cationic surfac- tants. Uptake of pyrrolidone carboxylic acid (PCA), a derivative of glutamic acid, is enhanced by combining with arginine, an amino with strong affinity towards hair. Effects of some amino acids on bleached/dyed hair are described. A hair conditioner incorporated with alanine improves hair surface hydrophobicity of bleach-damaged hair. Histidine and phenylalanine improve tensile strength. PCA was proved to be effective to improve color-retention of dyed hair. INTRODUCTION Protein is the second major component of living organism, following water. All proteins, including skin and hair, are various compositions of amino acids. Within the corneocytes, there is also a complex mixture of free amino acids and other low molecular weight, water-soluble compounds (Natural Moisturizing Factor or NMF)(l), and are known to contribute to maintenance of water balance in the stratum corneum. Amino acids, pyrrolidone carboxylic acid (PCA), lactate and urea, all compo- nents of NMF, are widely used in cosmetic fields and their usefulness is well established. Unlike in the case of the skin, the presence and the role of natural! y occurring free amino acids in hair shafts are not known yet. Although free amino acids are often detected in hair (2,3), they are more likely to be a product of protein degradation caused by UV or cosmetic treatment. But amino acids provided externally are known to interact with the hair to give various cosmetic effects, such as moisturizing, strengthening the hair (4), and retention of artificial color (5 ). In hair care applications it has been a long-experienced strategy to share the idea of skin care and utilize materials which are established in skin care applications. Vitamins, hydrolyzed proteins, vegetable extracts are good examples. This strategy is often proved to be so efficient that understanding of their basic interaction with hair tends to be left behind. In this paper, interaction between hair and various amino acids are discussed as well as the benefits of amino acids treatment. 347

348 JOURNAL OF COSMETIC SCIENCE MATERIALS AND METHODS MATERIALS Natural hair of Japanese women, 18 cm in length from tip end, was obtained from private source and subjected to measurement of physical properties. The hair was treated with bleaching lotion for 30 minutes at 33°C, rinsed thoroughly in running tap water, and this process was repeated 4 times. After the last bleaching, washing with 15% active sodium laureth sulfate solution, extensive rinsing and drying in a conditioned room (23°C, 40% RH.) followed. METHODS Uptake of amino acid. Japanese hair, treated with a waving lotion of thioglicolic acid and with a neutralizer of sodium bromate, was immersed in a solution of 11.5 mM amino acid. After 10 minutes the concentration of the amino acid solution was determined by HPLC method using an anion-exchange column and an electrochemical detector. Uptake of PCA. Intensively bleached Asian hair swatches, weighing 0.8 g each, were purchased from Beaulax (Tokyo, Japan). Each swatch was washed with a 15 wt% solution of sodium laureth sulfate for one minute, rinsed extensively with running tap water for one minute and air dried. A hair swatch was immersed in 6 ml of amino acid or PCA solution for 30 minutes. The swatch was rinsed in running tap water for 20 seconds and air dried overnight. For recovery of amino acid from the hair, the swatch was immersed in 15 ml of 1 0mM phosphoric acid buffer solution, pH 3.5. After 30 minutes, 10 ml of the buffer solution was removed for quantitative analysis. Concentration of the amino acid or PCA was determined by HPLC method. Hair conditioner treatment and hydrophobicity measurement. Hair conditioner (cationic sur- factant 0.6 wt% active, cetyl alcohol 3.0 wt%, 0.5 g per tress) was applied to wet hair and distributed manually for 30 seconds, then 30 seconds rinsing in running tap water (40°C) followed. The hair tresses were dried for more than four days in a conditioned room (23°C, 40% RH). A hair fiber was fixed in a horizontal position and 1 µl of deionized water was mounted on the point 10 cm from the hair tip end. Twenty seconds later the contact angle which the water drop and the fiber surface form was measured microscopically. Amino acid treatment and tensile strength measurement. A hair swatch was immersed in 100ml of 2 wt% amino acid solution at 35°C for three minutes. The swatch was then rinsed in 100 ml deionized water at 35°C for one minute, and air dried. Tensile measurements were performed on single fibers in deionized water. Hair fibers, 40 mm in length, were immersed in deionized water for at least one hour before the measurement and then extended at a rate of 20mm per minute on a tensile tester KES-G 1-SH (Kato Tech) to obtain force needed to extend the fiber by 20%. Color-retention effect Test I (Figure 1) Extensively bleached Asian hair swatches, purchased from Beaulax, were dyed with