Lecithin is a substance found in egg yolks, milk, and some plant and animal tissues. It's been used as a medicine to treat various ailments for centuries, such as hypercholesterolemia (high cholesterol), liver disease, and asthma. Nowadays it's also incorporated into cosmetics like eye makeup and lipsticks. It's mostly made of three types of fatty acids: glycerophosphates (g-6-p), phosphatides (2-3-p), and triglycerides (t3). The glycerophosphates comprise about 40% of lecithin's weight.

Lecithin was first isolated from egg yolk in 1843, and for a while, the word "lecithin" was used to refer to any fat-like substance found in foods. It wasn't until 1907 that a chemist named Meyerowitz differentiated between two types of lecithin: one from animal sources, which he called "lipoid" (later called phosphatidylcholine), and the other from plants, which he called "cephalin" (later renamed cephalins). In 1936, Haarmann and colleagues took Meyerowitz's phosphatide to heart and determined that the name "cephalin" was inappropriate. They suggested that instead cephalins should simply be called "lecithin".