Lecithin is a natural mixture of polar and neutral lipids; the word lecithin is also used as the trivial name of a particular phospholipid: phosphatidylcholine. Main vegetable
sources of lecithin used in personal-care products are soybean and maize, egg yolk is practically the only animal source of lecithin used in cosmetics and toiletries. The percentage of polar lipids and their fatty acid pattern are characteristic of the lecithin source.

Bare lecithin, a secondary product of Soya oil extraction, typically contains 60 to 70% polar lipids (mainly phospholipids, namely phosphatidylcholine, and glycolipids) and a remaining 25 to 35% Soy oil. This raw lecithin is further fractionated, purified, and chemically modified to allow easier processing and formulation in toiletry products. Emollient, refattening, and moisturizing properties of lecithin are guided by its content in phospholipids.

Lecithin softens, nourishes, and refattens the skin; it provides a nongreasy, long-lasting skin feel and improves foam feel and quality (creaminess, slipperiness, richness).
Ready-to-use mixtures of phospholipids in surfactant solutions, free of residual Soya oil, are commercially available for an easy incorporation in liquids or bars; some of these compounds allow formulation of clear products.

Source: Handbook of Cosmetic Science and Technology - André O. Barel, Marc Paye, Howard I. Maibach