Cosmet. Sci., 52, 103-118 (March/April 2001) Ultraviolet damage on natural gray hair and its photoprotection TAO GAO and ANN BEDELL, Croda Inc., North American Technical Center, 180 Northfield Avenue, Edison, NJ 08837. Accepted for publication February 28, 2001. Synopsis The physicochemical properties of natural gray hair obtained from the heads of individuals and as well as commercial samples were investigated. No statistically significant differences were observed in terms of their central maximum diameter, central cross-sectional area, central ellipticity, average tensile strength, and average extent of transverse swelling between gray and black hair. The correlation between the elongation and the contraction of the cross-sectional area of hair fibers during extension was established as a statistically linear function, with a coefficient of 0.758. The damage on natural gray hair from ultraviolet (UV) irradiation were assessed by measuring the following parameters: hair color, Young's modulus, stress-to- break, wet combing force, dynamic advancing contact angle, tryptophan damage, cuticle abrasion, and transverse swelling of hair fiber in 0.1 N NaOH solution. It has been found that gray hair undergoes more severe UV damage and needs more UV protection than dark brown hair. Experimental results indicate that the quaternized UV absorber, cinnamidopropyltrimonium chloride (CATC), delivered from a simple sham- poo system, is more substantive on hair and more effective in protecting hair from UV damage than a conventional UV filter. CATC also provided an additional conditioning benefit on hair. INTRODUCTION The influence of sunlight and ultraviolet (UV) light on both untreated and cosmetically treated human hair has been studied extensively by a number of researchers. Recently Ratnapandian et al. (1) studied the role of moisture in the photolysis of melanin-free virgin Piedmont hair and presented a free-radical mechanism to explain the photolysis processes. Changes in wet mechanical properties, swelling behavior, and IR spectrum were monitored and used to determine the degree of damage. The authors observed that hair exposed to UV irradiation sustains weathering damage under all conditions of relative humidity and found that exposure at 30% RH causes the least damage. Hoting and Zimmermann (2-4) studied photochemical alterations in human hair and sunlight- induced modifications in bleached, permed, and dyed-brown human hair. They mea- sured changes in hair color, tensile strength, and lipid compositions before and after irradiation with UV-A, UV-B, visible (VIS), and IR light. They found that blond hair is less photostable than black hair and that chemically treated hair exhibits significant color fading and yellowing after UV exposure. They also reported that chemically bleached hair needs additional protection against photochemically induced protein and 103

104 JOURNAL OF COSMETIC SCIENCE lipid modifications. Jachowicz et al. (5) and Pande and Jachowicz (6) used fluorescence spectroscopy to quantify tryptophan photodecomposition after UV irradiation. They found that weathering caused hair to undergo a significant loss in tryptophan, as well as other chemical changes affecting keratin structure, such as the oxidation of disulfide bonds to cysteic acid. Deftandre et M. (7) investigated photoaging and photoprotection of natural hair using the FT-IR technique and found that water inside the hair fiber is a necessary prerequisite to photooxidation or photobleaching of hair during UV expo- sure. They concluded that natural melanin in the hair is, at most, a weak means of protecting hair against the photodegradative action of solar light. Giesen et M. (8) studied the hair protection behavior of different UV filters and found that broad- spectrum filters such as benzophenones were particularly effective in protecting hair against discoloration and against losses in fiber strength and breaking force. They also observed that an oil-based product such as a shine spray containing oil-soluble UV filter was more effective in UV protection than setting lotions, which contained water-soluble UV filters. Gonzenbach et M. (9) studied UV damage on human hair and compared ten different UV filters. Their findings suggest that the choice of UV filter and the careful optimization of the formulation are crucial in developing a final product that can protect human hair from solar UV effectively. They used a colorimetric method to analyze the content of tryptophan in the hair before and after UV irradiation. They also found that blond hair is more susceptible to UV damage than black hair. Korner et M. (10) studied changes in the content of 18-methyl eicosanoic acid (18-MEA) in wool after UV irra- diation. They found that exposing wool fabric to artificial sunlight resulted in a loss of approximately 45% of the original 18-MEA content and that the branched-chain fatty acid 18-MEA was more sensitive to UV irradiation than the saturated, straight-chain acids with 16 and 18 carbon atoms. Until now there have been very few published studies on UV damage in natural gray hair. Only one paper, from Hollfelder and his co-workers, studied the chemical and physical properties of pigmented and non-pigmented (gray) hair (11). They found no statistically significant differences between pigmented hair and gray hair in terms of their fiber ellipticity and fiber break strength (wet). However, they observed that the average diameter of gray hair was statistically larger than that of pigmented hair and that the cystine content in gray hair was less than that in pigmented hair. They reported that gray hair showed a significant decrease in both wet breaking strength and cystine content after irradiation. After short periods of oxidation treatment, the level of cysteic acid in gray hair was found to be slightly higher than that in pigmented hair. They concluded that, in most cases, non-pigmented hair became more damaged after weath- ering than pigmented hair. However, no details about the test methods were reported. This paper represents the results of our recent studies on the physicochemical properties of natural gray hair and the effects of UV irradiation on these properties with and without UV protection. The central diameters, central cross-sectional area, central el- lipticity, extent of transverse swelling, stress-to-break, and strain-to-break of gray and black hair fibers were measured to determine if there were statistical differences between these types of hair. Gray and black hair samples were obtained from the heads of individuals for comparison. The UV study itself consisted of treating natural gray and virgin brown hair tresses with various and simple shampoo systems, which contain either a conventional UV filter or a quaternized UV absorber. Then the hair samples were irradiated with UV light for fifteen or twenty consecutive days. The following param-