JOURNAL OF COSMETIC SCIENCE 50 form of sodium ascorbyl phosphate (SAP), magnesium ascorbyl phosphate (MAP), and ascorbyl palmitate are widely used in cosmetic products (77). VITAMIN E. Vitamin E is the most important lipid-soluble antioxidant in the body. It is abundant in the sebum and acts to absorb the oxidative stress of sunlight and skin expo- sure. It has been demonstrated that vitamin E provides protection against UV-induced infl ammation and hyperpigmentation (78). Vitamin E has also been studied in combina- tion therapies with other vitamins as well as in other classes of skin-lightening com- pounds (79,80). Vitamins B, C, and E are used individually or in combination in many skin-lightening treatment therapies. (v) Peptides in skin lightening. Peptides are reported to reduce pigmentation through inter- action with the protease-activated receptor 2 (PAR-2) of keratinocytes. PAR-2 activation in involved in cell growth, differentiation, and infl ammatory processes and was shown to affect melanin and melanosome ingestion by human keratinocytes (81). The protease- activated receptor-2 upregulates keratinocyte phagocytosis. The peptide-based antago- nist for PAR-2 can be used to regulate melanin ingestion by keratinocytes, thus effecting skin-lightening. Short peptides have also been reported in reducing the enzymatic activity of tyrosinase (82). The use of sericin, a high-molecular-weight soluble glycoprotein from silk, as a tyrosinase inhibitor has also been documented (83). Peptide residues that act as MSH inhibitors have been known to lighten the skin. Soy trypsin inhibitors have been identi- fi ed as interfering in melanosomal transfer, thereby reducing skin pigmentation (84). (vi) Alpha and beta hydroxyl acids and derivatives. Alpha and beta hydroxyl acids have been the most important class of compounds that are most widely used in cosmetic prepara- tions. These act as superfi cial chemical peels that target the stratum corneum to improve skin color and tone. They are comparatively pure and inexpensive, and they may be used in higher amounts without many side effects (85). They are generally used in conjunction with other skin-lightening agents to improve performance. Also referred to as fruit acids, they improve skin texture by promoting desquamation or the shedding of the outer layers of the stratum corneum. Alpha hydroxyl acids (AHA) have also been noted to increase the enzymatic activity leading to epidermolysis. They are also employed in microderm- abrasion techniques. In addition, they act as moisturizers and promote the synthesis of elastin fi bers, leading to improved skin tone. However, care should be taken to neutralize the skin after AHA treatment, as it might cause burning and erythema. The most com- monly used AHAs are glycolic, lactic, citric, malic, pyurvic, and salicylic acids and their derivatives. THE EFFICACY OF SKIN-LIGHTENING FORMULATIONS Formulations for skin lightening have been majorly based on o/w emulsions that have a higher aesthetic appeal. The fact that many of the ingredients get better dispersions is also an added feature for the choice of such emulsions. Recently gel-based formulations are being considered for suitability in certain skin types. Effi cacy studies for skin-lightening formulations are carried out through clinical trails. Some of the techniques used in- volve the use of the mexameter, chromameter, spectrophotometer, and VISIA, along with

SKIN-LIGHTENING COSMETIC INGREDIENTS 51 dermatologist assessment. Also, other skin parameters such as moisturization, texture, barrier integrity, pH, etc, are being evaluated to give picture of skin health after the use of skin-lightening agents. This leads to screening the potentially harmful side effects of hydroquinone-like substances in addition to the high-value claim proposition for the cos- metics industry. With advances in technology in measurement techniques, it is becoming easier to identify the effi cacy of formulations in different skin types. CONCLUSION Research in the area of skin-lightening agents in an expanding fi eld, with new ingre- dients being added to the repertoire with every new discovery. Although tyrosinase inhibition is still the most sought after mechanism skin lightening, newer pathways are being identifi ed. It has been noted that ingredients that interfere with the path- ways affecting melanin synthesis and transfer show promise as depigmenting agents. Persistent research into skin lightening has also led to new mechanisms being discov- ered in recent years. The aspiration for light skin is on an upward curve and can be satisfi ed only when the cosmetic in the bottle fulfi ls the promise of fair skin. A careful and complete investiga- tion of the ingredient on the basis of its effi cacy and tolerance to individuals through clinical trails is essential to ascertain that the product delivers the promise. ACKNOWLEDGMENTS We thank Dr. Yash Kamath for reviewing the manuscript. Thanks are also due to Dr. Usha Ranganathan and Dr. Lakshmi Madhavi for their help in the preparation of the manuscript. REFERENCES (1) E. N. Glenn, Yearning for lightness, Gender & Society, 22(3), 281–302 (2008). (2) P. H. Eric, H. J. Li, R. W. Min, J. Belk, S. Kimura, and S. Bahl, Skin lightening and beauty in four Asian cultures, Adv. Consumer Res., 135, 444–449 (2008). (3) A. Gupta, M. Gover, K. Nouri, and S. Taylor, The treatment of melasma: A review of clinical trials, J. Am. Acad. Dermatol., 55, 1048–1065 (2006). (4) E. Berardesca, M. Ardigò, M. Berardesca, and N. Cameli, Melasma: Current and future treatments, Expert Rev. Dermatol., 3(2), 187–193 (2008). (5) A. E. Reszko, D. Berson, and M. P. Lupo, Cosmeceuticals: Practical applications, Dermatologic Clinics, 27, 401–416 (2009). (6) T. Kono, W. F. Groff, H. Sakurai, M. Takeuchi, T. Yamaki, K. Soejima, and M. Nozaki, Comparison study of intense pulsed light versus a long-pulse pulsed dye laser in the treatment of facial skin rejuve- nation, Ann. Plastic Surg., 59, 479–483 (2007). (7) T. Hakozaki, T. Hirotsugu, M. Kukizo, Y. Sato, and S. Arase, Ultrasound enhanced skin-lightening effect of vitamin C and niacinamide, Skin Res. Technol., 12, 105–113 (2006). (8) B. Green, R. Yu, and E. Van Scott, Clinical and cosmeceutical uses of hydroxyacids, Clinics Dermatol., 27, 495–501 (2009). (9) E. Clark and L. Scerri, Superfi cial and medium-depth chemical peels, Clinics Dermatol., 26, 209–218 (2008). (10) L. Petit and G. E. Pierard, Skin lightening products revisited, Int. J. Cosmet. Sci, 25, 169–181 (2003).