Cosmet. Sci., 54, 551-558 (November/December 2003) Comparison of antioxidant activity of extract from roots of licorice (Glycyrrhiza g/abra L.) to commercial antioxidants in 2% hydroquinone cream KATAYOUN MORTEZA-SEMNANI, MADJID SAEEDI, and BITA SHAHNAVAZ, Department of Medicinal Chemistry (K. M. -S., B.S.) and Department of Pharmaceutics (M. S.), Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran. Accepted for publication May 20, 2003. Synopsis Powdered dry roots of licorice (Glycyrrhiza glabra L.) were extracted with methanol. Licorice extract was tested for antioxidative activity in comparison with antioxidants (sodium metabisulfite and BHT) at 0.1%, 0.5%, 1.0%, and 2.0% w/w in 2% w/w hydroquinone cream. The systems were incubated in a dark room at 25 ø +_ 0.5øC and 45 ø _+ 0.5øC for three months. The physical stability and the percentages of hydro- quinone remaining after two weeks and one, two, and three months were determined by UV spectropho- tomerer at 294 nm according to official standard procedures. The experiment revealed that oxidation degradation of hydroquinone was accelerated by heat even with the existence of antioxidants. The higher percentages of remaining hydroquinone were observed for higher antioxidant concentration but showed lower physical stability in the formulation in the presence of commercial antioxidants, especially in the cases of 1.0% and 2.0% BHT. In the third month, at 25 ø _+ 0.5øC and 45 ø +_ 0.5øC, the extract demonstrated more antioxidant activity from two other commercial antioxidants at all concentrations, with about 43-53% and 34-46%, respectively, more hydroquinone remaining than in the control system (p 0.001). In the third month, the preparation containing 0.1%, 0.5%, 1.0%, and 2.0% extract gave good physical formu- lation stability with about 72%, 76%, 78%, and 81% hydroquinone remaining at 25 ø + 0.5øC and 51%, 55%, 60%, and 63% hydroquinone remaining at 45 ø + 0.5øC, respectively. This suggested the possibility of using a licorice extract at 0.5% and 1.0% as an effective natural antioxidant for substances that are oxidation-susceptible. INTRODUCTION One of the most important characteristics of many cosmetic products is stability. Hy- droquinone, a hypopigmenting agent employed percutaneously to lighten localized areas of hyperpigmented skin such as blemishes, lentigo, melasma, chloasma, and freckles, is known for its high oxidative reactivity. It is one of the chemicals that are difficult to Address all correspondence to Katayoun Morteza-Semnani. 551

552 JOURNAL OF COSMETIC SCIENCE stabilize. It becomes brown in air due to oxidation. One gram of hydroquinone is soluble in 17 ml of water and freely soluble in alcohol. In antifreckle and hair dyeing cosmetic products, a law limits its content to 2% w/w (1). Most hydroquinone products used in creams, gels, lotions, and ointments are locally manufactured in Iran. Being located in a tropical area, some Iranian people suffer from solar effects on their skin. Freckles are one of these effects. Hydroquinone is one of the cheapest hypopig- menting agents available in the Iranian market, which most middle and lower class Iranian people have preferred to use along with sunscreening products. However, with low stability and the side effects of allergy and irritation from hydroquinone for many consumers, the Cosmetic Control Division of Iran has special concerns for these products. In 1995, the FDA and the Toxicology Division of the Department of Medical Sciences, Ministry of Health, in Thailand reported that six out of 20 samples collected from the market contained more hydroquinone than the allowed amount. This was excused because of the high instability of hydroquinone, and most manufacturers had put the excess hydroquinone in their products in order to maintain a constant amount of 2.0% during storage (1). Recently, many researchers have been involved in finding means to prevent or delay deterioration by oxidative reactions in cosmetic preparations. A variety of antioxidants, both from natural sources and synthetic processes, are available in the market. In Iran, antioxidants that are usually incorporated in hydroquinone formulations are sodium metabisulfite (SM), BHT (butylated hydroxy toluene), BHA (butylated hydroxy anisole), ascorbic acid, vitamin E, citric acid, and/or combinations of these chemicals. Their shelf life is about one year. Hydroquinone itself has been used as an antioxidant in combi- nation with others in the concentration of 0.05-0.1% (2). Various disadvantages of some of these antioxidants have caused concern. For example, an application of BHA and BHT is now restricted in many countries, since undesirable effects from these additives on the enzymes of the liver and lungs can occur. Occasionally, the antioxidant ability of vitamin E is less active (1). More recently, research has focused on developing safer and more effective antioxidants from natural sources, such as Rosmarin•s officina/is L., Piper spp., Geranium pratensis, Germ •rban•m, Viola tricolor, R•mex acetosa, Ilex parag•ensis, Rosa sp., licorice root, cinnamon, ginger rhizomes, Capsicum spp. and green tea (3-10). Some of the chemical constituents (e.g., polyphenolic flavonoids) of Glycyrrhiza glabra have been identified as antioxidant agents it is possible that the synergistic effects of flavonoid mixtures may be responsible for the high activity observed in licorice extract (6,11-16). However, a study of the antioxidative activity of the extract from Glycyrrhiza glabra has never been performed for cosmetic preparations. Glycyrrhiza glabra L. is good for skin eruptions, including dermatitis, eczema, pruritus, and cysts. It has also anti- inflammatory, anti-infecting, antiseptic, antibacterial, antihepatotoxic, antiviral, and antiphlogistic properties. It is also used for gastric and duodenal ulcer (17). Glycyrrhiza glabra L. is native to Eurasia and cultivated in Europe (Spain, Italy, France, etc), the Middle East (Syria, Iran, Turkey, Iraq, etc), and Asia (e.g., China). The parts used are the dried roots collected in the fall (18). Hydroquinone, which is known for its high sensitivity to oxidation, has been chosen as an indicator for comparison of the antioxi- dative activity of licorice extract to commercial antioxidants in the form of 2% w/w hydroquinone cream.