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j. Soc. Cosmet. Chem., 44, 163-175 (May/June 1993) A simple and sensitive technique, based on protein loss measurements, to assess surface damage to human hair SUKHVINDER S. SANDHU and CLARENCE R. ROBBINS, Technology Center, Colgate Palmolive Company, Piscataway, NJ 08854-1340. Received October 14, 1992. Synopsis This article describes a simple yet sensitive technique to assess surface damage to hair. It is based on the hypothesis that the damaged hair surface is more susceptible to abrasion/erosion than undamaged hair, and involves shaking hair in water and quantitatively measuring the amount of protein abraded/eroded from the hair using a colorimetric procedure capable of detecting as little as 5 Ixg of protein per mi. With this procedure, we were able to demonstrate significant differences in hair damaged due to bleaching, permanent wave treatments, and Suprox (a diperisophthalic acid based oxidant), and even after extended treatment with different surfactants. Furthermore, hair with exposed cortex was found to be more susceptible to protein loss by surfactants and/or water than hair with intact cuticle. INTRODUCTION Hair fibers generally consist of three distinct morphological components, the outer protective layers known as the cuticle,' the major structural components, or the cortex,' and the porous components, or the medulla. The cuticle plays an important role both as a protective barrier and for many of the cosmetic properties of the hair, whereas the cortex provides mechanical strength to the hair fiber as a whole. It is known that the physi- cochemical properties of hair change as a result of damage to hair (1-3). Damage to hair may be confined to the surface layers (cuticle), or the whole fiber may be involved. However, cuticle layers are generally damaged before any damage can occur to the cortex. Therefore, damage tests that focus more on surface changes have the potential to be more sensitive than those that rely on whole fiber changes. Recently, one of the above authors (Robbins) demonstrated, using Suprox (a diperiso- phthalic acid based oxidant), that extensive damage to several cuticle (surface) layers of hair was readily observed microscopically without any detectable changes in the tensile properties (wet or dry) (4). These findings further support the hypothesis that tensile properties are due primarily to the cortex. Obviously, tensile properties are of little value to study cuticle or surface damage. This report describes a simple and sensitive tech- nique developed to assess surface damage to hair. Some investigators have shown that shaking animal or human hair in the presence of a liquid can be used to separate cuticle 163