The human skin surface and hair are generally coated with a thin film of liquid phase sebaceous lipids. This surface lipid film contributes to the cosmetic properties of the skin. Synthetic sebum has been used for studies on properties of skin and hair. However, there has been no standardized formulation of synthetic sebum and many of the synthetic sebum formulations that have been used do not closely resemble actual sebum. In this study, a formulation for a standardized and inexpensive synthetic sebum is proposed, and the chemical stability of this lipid mixture is demonstrated under conditions of use and storage. The proposed synthetic sebum consists of 17% fatty acid, 44.7% triglyceride, 25% wax monoester (jojoba oil) and 12.4% squalene. This lipid mixture takes up approximately 6% of its weight in water when equilibrated in an atmosphere saturated with water vapour. It is stable on exposure to the atmosphere at 32 degrees C for at least 48 h, and it is also stable on storage at 4 or -20 degrees C, either dry or in chloroform : methanol solution for at least 6 months. This synthetic sebum could be useful in studies on cosmetic properties of the skin surface or hair, on penetration of chemicals into the skin or in development of standardized tests of laundry detergent performance.