J. Cosmet. Sci., 66, 335–357 (November/December 2015) 335 Effect of formulation variables on the physical properties and stability of Dead Sea mud masks SAWSAN SHAHIN, *SAJA HAMED, and HATIM S. ALKHATIB, Faculty of Pharmacy, University of Jordan, Amman (S.S., H.S.A.), and Faculty of Pharmaceutical Sciences, Hashemite University, Zarqa (S.H.), Jordan. Accepted for publication September 20, 2015. Synopsis The physical stability of Dead Sea mud mask formulations under different conditions and their rheological properties were evaluated as a function of the type and level of thickeners, level of the humectant, incorpora- tion of ethanol, and mode of mud treatment. Formulations were evaluated in terms of visual appearance, pH, moisture content, spreadability, extrudability, separation, rate of drying at 32°C, and rheological properties. Prepared mud formulations and over-the-shelf products showed viscoplastic shear thinning behavior satis- factory rheological behavior was observed with formulations containing a total concentration of thickeners less than 10% (w/w). Casson and Herschel–Bulkley models were found the most suitable to describe the rheological data of the prepared formulations. Thickener incorporation decreased phase separation and im- proved formulation stability. Bentonite incorporation in the mud prevented color changes during stability studies while glycerin improved spreadability. Addition of 5% (w/w) ethanol improved mud extrudability, slightly increased percent separation, accelerated drying at 32°C, and decreased viscosity and yield stress values. Different mud treatment techniques did not cause a clear behavioral change in the fi nal mud preparation. B10G and K5B5G were labeled as “best formulas” based on having satisfactory physical and aesthetic criteria investigated in this study, while other formulations failed in one or more of the tests we have performed. INTRODUCTION The Dead Sea is the most concentrated hypersaline area in the world it has an average salinity of 370 g salt per kilogram of water, compared with the ocean’s average salinity of 35 g salt per kilogram of water (1). As the name indicates, this sea is devoid of life, except for salt-tolerant halophilic anaerobic bacteria (2). Potassium chloride, magnesium chloride, calcium chloride, sodium chloride, and their corresponding bromides constitute the major salt components of the Dead Sea, comprising about 98% on a dry weight basis (3). Address all correspondence to Saja Hamed at hamedsh@hu.edu.jo *Current affi liation: Faculty of Pharmaceutical Sciences, Hashemite University, Zarqa, Jordan

JOURNAL OF COSMETIC SCIENCE 336 Dead Sea mud is a suspension of very fi ne clay particles in water (4) it is the natural sediment of solid mineral clays with an interstitial solution of inorganic salts and sulfi de compounds that arise from microbiological activity (5). It is characterized by its blackish color and the distinct sulfur smell (1). In addition, at 25°C, it has a pH of 6.4–7.6, density of 1.6–1.8 g/l, water content of 30–40%, nonpatho- genic microbial content of less than 100 CFU/g, and 86–98% of particles with size less than 5 mm (5). The therapeutic effect of Dead Sea mud is related to its high mineral content and ability, due to its black color, to retain heat for many hours (3). In general, Dead Sea mud is used as packs for the treatment of rheumatic disorders such as myalgias, neu- ralgias, and osteoarthritis masks to treat cutaneous skin disorders such as acne, der- matitis, psoriasis, xerosis, and eczema and baths to treat lipodystrophy and cellulite (6,7). In addition, Dead Sea mud and salts have been widely used in cosmetic and personal care products including lotions, masks, soaps, creams, and shampoos (1,3). The formulation and processing of Dead Sea products is not a simple undertaking, and should be tackled using valid scientifi c and technical approaches. For example, the formulation of cosmetic emulsions containing Dead Sea salts is known to give rise to production and stability problems and development scientists must take into consideration the maximum salt level that can be incorporated into a formulation without affecting stability, consistency, and liquid phase separation while maintain- ing effi cacy (8). On surveying the commercially available Dead Sea mud mask products in the Jordanian market and interviewing technical and quality staff of Dead Sea products manufacturers, we have identifi ed phase separation, stability issues as well as diffi culty in processing, and fi lling as the major problems in this product category. Rational use of formulation additives can improve the properties of mud formulations. These additives include thickeners that are expected to decrease phase separation of fi n- ished product, humectants that may be used to prevent dehydration, and ethanol that accelerates mud drying after application onto the skin. This study was initiated to evaluate the effects of commonly used additives in Dead Sea mud formulations as well as mud treatment techniques on the physical properties, rheology, stability, and aesthetic acceptance of the fi nished mud products. MATERIALS AND METHODS MATERIALS Dead Sea mud was provided by Numeira Mixed Salts & Mud Company Ltd. (Amman, Jordan), bentonite (Al2O3.4SiO2.H2O) was purchased from Vickers Laboratories Ltd. (West Yorkshire, England), kaolin (Al2H4O9Si2) was purchased from Merck (Darmstadt, Germany), Natrosol® 250 HHX (hydroxyethyl cellulose) was provided by Ashland Inc., (Wilmington, DE), and glycerin (99.5%) and ethanol pure (96%) were obtained from AZ-Chem (Selangor, Malaysia).