JOURNAL OF COSMETIC SCIENCE 428 CONCLUSION There are many known benefi ts for the use of alpha-hydroxy acids on skin. There have also been recent reports that topical treatments with alpha-hydroxy acids increase skin dam- age resulting from UVB. Additionally, high concentrations of alpha-hydroxy acids have also been found to promote irritation. In order to fi nd alternatives to alpha-hydroxy acids, we investigated a variety of amino sugar compounds that were previously reported to inhibit the reaggregation of dissociated corneocytes by modulating cellular adhesion. Human keratinocytes in culture treated with 50 mM to 250 mM of NAG were released from the culture dish. This treatment appears to dissociate the keratinocytes from each other and from substrates. In addition, we observed an upregulation of differentiation markers, keratin 10 and involucrin, in keratinocytes treated with NAG. In vivo, we observed that topical treatments with a formulation containing NAG led to an increase in skin moisture levels and the normalization of stratum corneum exfoliation. In addition, high concentrations of NAG do not cause any noticeable irritation (data not shown). Topical doses as high as 5% and 10% did not produce any skin irritation. The benefi ts of topical N-acetyl-glucosamine are numerous and have been well documented by Bissett (11). These include accelerated wound healing, reduction of hyperpigmentation, and improved skin hydration. We have added to these benefi ts by showing an exfoliation enhancement. We propose the use of amino sugars, such as N-acetyl-glucosamine, as alter- native compounds to replace the use of alpha-hydroxy acids in skin care. REFERENCES (1) E. J. Van Scott and R. J. Yu, Control of keratinization with alpha-hydroxy acids and related compounds. I. Topical treatment of ichthyotic disorders, Arch. Dermatol., 110, 586–590 (1974). (2) M. J. Stiller, J. Bartolone, R. Stern, S. Smith, N. Kollias, R. Gillies, and L. A. Drake, Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin. A double-blind vehicle-con- trolled clinical trial, Arch. Dermatol., 132, 631–636 (1996). (3) N. V. Perricone, and J. C. DiNardo, Photoprotective and antiinfl ammatory effects of topical glycolic acid, Dermatol. Surg., 22, 435–437 (1996). (4) E. J. Van Scott and R. J. Yu, “Substances That Modify the Stratum Corneum by Modulating Its Formation,” in Principles of Cosmetics for the Dermatologist, P. Frost and S. N. Horwitz, Eds. (C. W. Mosby, St. Louis, 1982), pp. 70–74. (5) M. M. Brysk, S. Rajaraman, P. Penn, and E. Barlow, Glycoproteins modulate adhesion in terminally differentiated keratinocytes, Cell Tiss. Res., 225, 657–663 (1988). (6) D. L. Hudson, J. Sleeman, and F. M. Watt, CD44 is the major peanut lectin-binding glycoprotein of human epidermal keratinocytes and plays a role in intercellular adhesion, J. Cell Sci., 108, 1959–1970 (1995). (7) D. Cerimele, C. Del Forno, and F. Serri, Histochemistry of the intercellular substance of the normal and psoriatic human epidermis, Arch. Dermatol. Res., 262, 27–36 (1978). (8) S. Sakai, R. Yasuda, T. Sayo, O. Ishikawa, and S. Inoue, Hyaluronan exists in the normal stratum corneum, J. Invest. Dermatol., 114, 1184–1187 (2000). (9) P. Boukamp, R. T. Petrussevska, D. Breitkreutz, J. Hornung, A. Markham, and N. E. Fusenig, Normal keratinization in a spontaneously immortalized aneuploid human keratinocyte cell line, J. Cell. Biol., 106, 761–771 (1988). (10) J. C. Adams and F. M. Watt, Expression of beta 1, beta 3, beta 4, and beta 5 integrins by human epidermal keratinocytes and non-differentiating keratinocytes, J. Cell Biol., 115, 829–841 (1991). (11) D. Bissett, Glucosamine: An ingredient with skin and other benefi ts, J. Cosmet. Dermatol., 5, 309–315 (2006).

J. Cosmet. Sci., 60, 429–436 (July/August 2009) 429 Address all correspondence to M. Scalzo. Colorimetric investigation of the reaction between p-phenylendiamine and meta-substituted derivatives of benzene on a model support M. SCALZO, M. STRATI, M. A. CASADEI, F. CERRETO, and S. CESA, Dipartimento di Chimica e Tecnologie del Farmaco, Università di Roma “La Sapienza,” Piazzale Aldo Moro 5, 00185 Rome (M.Sc., M.A.C., F.C., S.C.), and Tocco Magico, Via dei Monti Tiburtini 770, 00157 Rome (M.St.), Italy. Accepted for publication February 11, 2009. Synopsis The aim of this work was the employment of colorimetric techniques in the analysis of the color formed, on a proteic substrate, by the reaction between p-phenylendiamine and some meta-substituted benzene deriva- tives in the presence of hydrogen peroxide and in media at different pH values. In particular we investigated the chromatic variations that take place on the substrate in dependence on different reaction conditions. The obtained results show that for each couple of reagents the colorimetric data, namely the refl ectance of the formed color, change considerably with the pH of the reaction medium and demonstrate how this parameter can be considered a good descriptor of the composition of the formed pigment. INTRODUCTION The reaction of p-phenylendiamine (PPD, precursor) with meta-derivatives of benzene, having amino and/or hydroxy groups as substituents (couplers), is widely applied in oxi- dative hair dyeing. The general pathway of these reactions has been explained by Corbett (1–7) (Figure 1), who has pointed out that it is not unique, is affected by the reagents’ concentration, and is strongly sensitive to the pH of the solution. The p-quinone di-imine 1, or rather its conjugated acid 2, is the key species of the whole process of dye formation. According to Corbett, at pH 8 and using ferricyanide as oxi- dant, the oxidation of p-phenylendiamine (PPD) to the di-imine 1 is quantitative and very fast (1). Even if the reaction kinetics may vary with different couplers, the indo dye 3 is the main product because in these conditions the self coupling of p-phenylendiamine, which yields the Bandrowski’s base 4, may be considered negligible. In contrast, with hydrogen peroxide, the rate of formation of the di-imine 1 is slow and the indo dye 3 can react with the unoxidized p-phenylendiamine, leading to molecule 5, which is considered