114 JOURNAL OF COSMETIC SCIENCE HYDROQUINONE: CONTROLLED EFFICACY AND SAFETY Howard I. Maibach, M.D. and Terry Oldman* Dept. of Dermatology, Univ. of California, San Francisco, CA 94143, *Eastman Chemical Company, Kingsport, TN 37662-5230 Introduction Hydroquinone (HQ) has been formulated for decades into creams, lotions, and gels for treatment of disfiguring hypcrpigmentation. These skin-lightening products are sold as cosmetics or as over-the-counter (OTC) and prescription drugs depending on the regulations in the respective country. In the USA, HQ was reviewed by the FDA (1978 and 1982) and was found to be the only active ingredient considered safe and effective for skin bleaching provided the concentration is in the range of 1.5 - 2.0%. HQ that meets the requirements of the United States Pharmacopeia (USP Grade) is required for this application, which ensures safety, effectiveness, and consistent purity and potency in skin lightening drug products. In vitro and in vivo studies continue to provide a greater understanding of the efficacy and safety of HQ. Efficacy Studies Even though the FDA monograph refers to HQ as a "skin bleaching active ingredient," it does not literally bleach the melanin in the skirt: Instead, HQ inhibits the production of melanin by reversing the tyrosinase-catalyzed conversion of DOPA (dihydroxyphenylalamne) to dopaquinone. HQ may also compete with tyrosine as a substrate for tyrosinase, limiting the formation of DOPA. The suppression of melanin synthesis by skin lightening agents is discussed in detail by Prota. 2 The tyrosinase inhibition effects of HQ have been compared to other skin lightening agents: arbutin, kojic acid, and ascorbic acid, in an in vitro study conducted by Maeda and Fukuda) Human melanocytes were cultured with each skin lightening agent in multi-well plates for three days, and the tyrosinase activity was assayed using L-DOPA as a substrate. The study also includes a comparison of the effect of each slda lightening agent on melanocyte viability. Figure I shows the concentration at which each agent effectively reduced tyrosinase activity by 40%, aad also the concentration at which the melanocyte cell survival number is equal to or less than that of the control. HQ is a tyrosinase inhibitor at much lower concentrations than the other three agents. HQ also has a cytotoxic effect at lower concentrations than the other agents but all of the agents show cytotoxic effects. The •vindow between the concentration providing significant tyrosinase inhibition aad the onset of cytotoxicity is the widest for HQ, there being a 10-fold difference. Two in vivo human studies were conducted by Burke, Maibach, and Stxauch, to determine the relative skin lightening effect of a 2% HQ commercial cream. In the first study, a significant change in skin color of type 3 & 4 skin was observed follo•ving 9 weeks of therapy on the backs of normal volunteers. n Color of the skin throughout the stud)' was measured with a Photovolt 577 reflectometer. Results showed greater skin depigmentation for darker skin types compazed to lighter skin types. A latency period of 4 - 7 weeks occurred at the beginning of the study prior to the onset of depigmentation (see Figure 2). The second study was performed to determine the relative depigmentary action of a commercial cream on females with facial melasma. s Treatment consisted of 50-100 mg of 2% HQ cream applied twice daily for Fifteen weeks. A Minolta Chroma Meter CR-300, "L" scale, was used to measure the lightness of the skin. The hyperpigmented facial area •vas lightened as evidenced by an average increase of 2.4 reflectance units over the Fifteen-week treatment. The greatest degree of depigmentary action was observed after ten weeks of treatment, with no further depigmentation observed in the last five weeks of the study. • t O.I • O.Ot Figure 1. Concentration of Reduced Tyroslnase Actlvlb/ Compared to Reduced Cell V1ablllb/ HQ Arbut,n Kojlc Acid Ast.•'bJc ACid I • Reduced Tyroslrmse ActMIy by 40% L O Reduced Cell Vlab•51y i Figure 2. Ret'lectance for HQ Treatment Sites Adjusted for Control Graph Presenm Deta I'or Sul•ecm wJttl Trial Mean Reflectance Levels al Baseline of 30 units DR z 30 Unl• • -- 3o Uni• at B• • Trial Week

PREPRINTS OF THE 1999 ANNUAL SCIENTIFIC SEMINAR 115 Adverse Dermal Effects Widespread research has been conducted on the usage of HQ, and in some of these studies HQ has been documented as a contact allergen. However, a critical review of HQ patch test studies concluded that none of the studies performed Repeated Open Application Tests (ROATs) and Provocative Use Tests (PUTs) to differentiate between irarant and allergic responses. 6 Therefore, the frequency of HQ allergic contact dermatitis cannot be estimated. In only one of the studies was there an exclusive HQ patch test trial. 7 Bentley-Phillips and Bayles found little or no irritant reaction at concentrations of 1, 2.5, and 3.5% HQ in standard 48-hr closed patch tests. However, at HQ concentrations of 5 and 7%, 83.6% of the patch tests showed positive reactions, which were presumably irritant. Exogenous ochronosis in Blacks is a relatively unknown condition in the USA, but a relatively high incidence has been observed in South Africa. 8 One of the reasons is that prior to 1984, neither the type nor concentration of skin lightening compounds sold in South Africa was regulated. It was not uncommon for skin lightening products to contain 6 - 8% HQ. Also, the combination of high HQ concentrations together with other preparations containing agents such as phenol and resorcinol provided the basis for the high incidence of ochronosis. In Goldemberg's discussion of this problem, he auributed the high incidence of ochronosis to the use of monobenzone (hydroquinone monbenz3'l ether), in addition to high concentrations of HQ) Derreal Absorption Studies and Toxicity Chronic oral exposure of F344 rats to HQ has been reported to cause renal cell adenomas. 9 Studies involving sub-chronic oral exposure of F344 rats have shown nephrotoxicity and renal tubule cell proliferation) ø A more recent stud).' was conducted by R. David, et al, • to determine whether dermat exposure to HQ cream would result in earl), cellular events similar to those observed after oral exposure to HQ. F344 rats, a strain known to be sensitive to HQ, were given topical applications with 0, 2.0, 3.5, or 5.0% HQ in an oil-D-water emulsion cream for 13 weeks (5 days/week). Cell proliferation in the kidneys was evaluated after 3, 6, and 13 weeks of trealxnent. The study showed that dermal exposure to HQ- containing creams does not result in systemic toxicity. No changes indicative of sustained cell proliferation were seen, and the renal lesions noted after oral exposure to HQ were not present after derreal exposure. David, et at, concluded that the systemic toxicity of HQ in F344 rats is limited by its slow dermal absorption rate and rapid excretion rate. HQ dermal absorption rates in rats and humans have been studied extensively, m vitro and in vivo. •2a3 Conclusion It is apparent that the efficacy and safety of HQ has been studied extensively, more so than any other skin lightening agent. HQ is recognized as the most efficacious of the skin lightening agents now under review. At the same time, HQ is being criticized for being cytotoxic, and for cansing exogenous ochronosis and cutaneous Lrritation. 14'15 This brief review has attem!•ed to explain the conditions under which the various negative effects of HQ have been observed and serves to clarify the conditions under which HQ can be used safely. Kidney toxicity that was observed in animals fed HQ by stomach tube was not apparent in derreal studies. Cytotoxicity, which has been observed in vitro, has not been observed in vivo and evidence indicates that adverse skin reactions such as ochronosis and irritation have occurred at HQ concentrations greater than 4%. The maximum concentration of 2% HQ is a responsible use level for OTC drug products as recognized by the FDA while the use of products containing higher concentrations of HQ should be controlled carefully under a physician's supervision. R. Goldemberg, Compounder's Corner, DCI, p 54 (February 1997). G. Prota, Melanins and melanogenesis, Cosmetics & Toiletties, 111, 43 (1996). K. Maeda and M. Fukuda, In vitro effectiveness of several whitening cosmetic components m human melanocytes, J. Soc. Cosmet. Chem., 42, 361 (1991). Burke, H. Maibach, and E. Strauch, Photometric quantification of relative depigmentary activity of hydroquinone on normal skin, submitted to the Y. of Dermatological Treatment (1999). Burke, H. Maibach, and E. Stmuch, Colorimetric quantification of the relative depigmentmg activity of hydroquinone on melasma, submitted to the ,L of Dermatological Treatment (1999). D. Lalloo, S. Makar, and H. Maibach, Hydroquinone as a contact allergen, Dermatosen, 45, 208 (1997). B. Bentley-Phillips and M. Bayles, Cutaneous reactions to topical application of hydroquinone - Results of six year investigation., SouthAft. Med. d. 49, 1391 (1975).