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j. Soc. Cosmet. Chem., 48, 41-50 (January/February 1997) The effect of formulation on the hardness and crystallization of emulsion lipsticks TSUI-SHUANG WANG and GINGER LEE, Department of Applied Chemistry (T.-S.W.) and Department of Cosmetic Science (G.L.), Chia-Nan College of Pharmacy and Science, Tainan 717, Taiwan, R.O.C. Received j•r publication April 15, 1997. Synopsis Emulsions can improve the emollient property of lipsticks because of the introduction of hydrophilic ingredients. A lipophilic emulsifier (Span 60 or Span 80) or a hydrophilic emulsifier (Tween 20) was used to prepare emulsion lipsticks. The experimental results show that a hydrophilic emulsifier is as good as a lipophilic emulsifier. Both of them give stable W/O emulsion lipsticks that also have similar values of hardness (or stiffness). A comparison of physical properties of emulsion lipsticks was made with a conventional lipstick. An emulsifier has a good compatibility with waxes and thus decreases the crystallization, which also decreases the hardness. On the contrary, the formation of emulsion droplets increases the hardness of lipsticks. The effect of water content on the physical properties of emulsion lipsticks is also discussed. INTRODUCTION Lipsticks are very common color cosmetics. Most women apply lipsticks, especially when they go out. The essential factors are pleasant smell, luster, color, stability, safety, adhesion, and extensibility. A panel test is the most popular and direct method to understand what customers prefer (1). Usually customers are concerned very much about the feel, color, and lasting effects of lipsticks. There was a revolution in lipsticks after 1980, both in shape and ingredients. On the one hand, lipsticks were sold in a slim design, with elliptical and even multiple-sided cross-sections. On the other hand, new ingredients were introduced to improve the function of the lipsticks (1-7). Castor oil derivatives with hydroxy groups, carboxyl groups, and double bonds can increase adhesion to the lip surface (1). Lanolin derivatives can improve adhesion and luster (5), and silicones (6,7) can reduce the surface energy and thus reduce friction, providing a good feel and good extensibility in lipstick formulae. Moisturizers, such as ethylene glycol and polysaccharides, have been used in lipsticks to prevent the lips from drying and cracking. However, moisturizers are not compatible 41