j. Soc. Cosmet. Chem., 44, 109-122 (March/April 1993) Hair photodamageMeasurement and prevention CHANDRA M. PANDE and JANUSZ JACHOWICZ, Clairol Inc., 2 Blachley Road, Stamford, CT 06922. Received July 27, 1992. Presented in part at the Annual Meeting of the Society of Cosmetic Chemists, New York, December 1991. Synopsis A spectroscopic technique, based on the intrinsic fluorescence of hair keratin, has been used to monitor the concentration of tryptophan in hair. Experiments performed by using either artificial light or natural sunlight have shown that tryptophan is photolabile, and undergoes decomposition on exposure to UV light in the 295- to 315-nm range. Hair weathering was found to produce significant loss of tryptophan, together with other chemical changes in the keratin structure such as the oxidation of disulfide bonds to cysteic acid. Thus it is shown that tryptophan in hair can serve as a sensitive marker of hair photodamage. It is also demonstrated that hair care formulations containing sunscreens can reduce the extent of photodamage. Furthermore, the tryptophan decomposition rate was found to be substantially slower in mineral oil-treated hair, compared to water-treated control. These data suggest that hair care formulations containing non- chromophoric material may also reduce photodamage. INTRODUCTION Hair fibers are made up of fibrous proteins belonging to the keratin family. Minor contribution to the total hair mass derives from melanin pigment and lipids. Morpho- logically, hair structure has two distinct components. The shingle-like cuticles form the hair exterior and enclose the corticular mass. The latter consists of tightly packed elongated cortical cells oriented parallel to the fiber axis. These cells contain or-helical microfibrils in a supramolecular motif, embedded in a cystine-rich amorphous protein matrix. These different protein components comprising the hair fiber have distinctly different amino acid composition (1-3). Recent reports on the harmful effects of sunlight on human skin have raised the aware- ness of the deleterious effects of sunlight on biological tissues in general. Hair, though not viable, can also undergo photodegradation (4), which can contribute significantly to the overall hair damage (5). The lack of viability of hair, however, precludes straight- forward measurement of damage based on tissue response analogous to skin erythema. Thus, there is an obvious need for a sensitive intrinsic marker of hair photodamage. Hair weathering results in discoloration due to melanin bleaching, as well as damage to hair keratin (5). While the pigment decomposition is apparent, the damage to the fiber itself is not easily discernible. The most dramatic effect is found to be the oxidation of 109

110 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS cystine disulfides to cysteic acid. Although long-term exposure of the fibers to UV light is known to affect their mechanical properties (4,6), even shorter irradiation may pro- duce cosmetically undesirable effects such as a loss of luster or an increase of hair resistance to combing (7). There could also be a more subtle damage at the molecular level, which can initiate a cascade of reactions that may eventually produce undesirable effects. The essential first event in hair photodamage, as in all photoprocesses, is light absorp- tion by the fiber. Only wavelengths above 290 nm will be consequential in natural photodamage, since shorter wavelength UV light will be effectively filtered out by the stratosphere (8). The most significant chromophores in proteins that absorb in the UVB region are the amino acids, tyrosine (Tyr, kma • = 275 rim, ½290 = 100 M- • cm-•), tryptophan (Trp, k•na• -- 280 rim, ½290 = 4500 M- • cm- •), and the disulfide bonds (kma • 200 rim, ½290 = 40 M- 1 cm-l) (9-11). Phenylalanine, another aromatic amino acid, absorbs only in the UVC region and, therefore, is not likely to participate in the photodamage reactions of proteins. The longer wavelength UVA and visible light are not likely to cause damage directly since they are not absorbed by proteins. Thus, of all the chromophores in keratin, only tryptophan (Trp) absorbs significant UVB (290-320 nm) light and is, therefore, likely to be most photolabile. This has, indeed, been clearly demonstrated in the case of bovine eye lens crystallines (12, 13). It is surprising that Trp has received little attention in hair research, and except for a few reports (14-17), Trp is often missing in the published compilations of the amino acid composition of human hair keratin. The estimates for the Trp content of hair range from 0.2% to 1% (3,14,15,17). Such a significant source-to-source variation may have arisen, at least in part, because of the photolability of this amino acid, which is discussed in this report. On the other hand, a significant body of literature exists on Trp pho- todamage in weathered wool and on its role in the photo-yellowing of wool (18-20). Fluorescence measurements have also been reported on wool cloth (21,22). Furthermore, examples of the deleterious effects of Trp photochemistry, including sensitization of non-chromophoric amino acids, abound in the protein literature. Thus, Trp seems to play a significant role in the photochemistry of keratins and of proteins in general. The objective of this work was to study the process of photodecomposition of Trp in human hair by using fluorescence spectroscopy. The underlying motivation was the need to develop a sensitive intrinsic marker of hair photodamage that could then be used to assess the efficacy of hair care formulations designed to provide photoprotection. We show here that Trp, indeed, provides a very sensitive indicator of hair photodamage. Using this assay we show that conventional UVB sunscreens in hair care formulations can provide photoprotection. Furthermore, our data suggest that non-chromophoric compounds, such as mineral oil, also reduce hair photodamage. EXPERIMENTAL Experiments were routinely performed on Piedmont hair (Commercial white, DeMeo Brothers, New York) unless otherwise stated. Naturally weathered hair was obtained from a 7-yr-old Caucasian child and was compared to intact hair from the same source. All amino acids were from ICN Pharmaceuticals.