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Oil is a substance that is liquid at room temperature and insoluble in water. Synthetic oils include mineral oil and petrolatum, which are derived from the distillation of petroleum in the production of gasoline. Vegetable oils are pressed out of seeds, and essential oils are steamed from several plant parts, including stems, leaves, and roots. The Cosmetic Ingredient Review (CIR) categorizes vegetable oils in the larger class of edible oils. Edible oils, such as peanut oil, are refined in a process that removes proteins that can cause sensitization in allergic individuals.1 Manufacturers of animal-derived oils, such as lanolin, have to follow strictly certified processes in order to eliminate any risk of infectious agents.
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Most oils and fats are triglycerides, which are composed of glycerol and fatty acids. Natural triglycerides contain the five most common fatty acids in various proportions: palmitic, stearic, oleic, linoleic, and linolenic acids.
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Oils contain a large variety of fatty acids, with stearic, oleic, and linoleic acids among the most abundant.2 The fatty acid profile for a certain oil helps to determine the oil’s characteristics with respect to skin feel, substantivity, occlusive ability, penetration, biologic activity, and stability. Stability is influenced by susceptibility to oxidation: fatty acids with a higher degree of unsaturation are oxidized more easily. Essential fatty acids (EFAs) are those that the body cannot synthesize and, therefore, must be obtained topically or in the diet. Vegetable and fish oils contain EFAs such as ω-6 and ω-3 fatty acids. EFAs influence skin barrier function, membrane fluidity, cell signaling, and the inflammatory eicosanoid pathway. Nonessential fatty acids and EFAs play important roles in skin function.
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Linoleic acid is an EFA. Several edible oils contain linoleic acid. Linoleic acid is an unsaturated ω-6 fatty acid present in many oils including sunflower and safflower (Table 9-1). In addition to providing structural lipids needed for barrier integrity, linoleic acid is used by the body to produce γ-linolenic acid (GLA). GLA is a polyunsaturated essential cis-fatty acid important in the production of prostaglandins; therefore, it plays a role in the inflammatory process.
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Oleic acid is technically not an EFA because the body can produce a small amount; however, it is a very important fatty acid for the skin. Oleic acid has a polar head group attached to a long alkyl chain.3,4 This structure allows it to disrupt the barrier by inserting ...