What ingredient is commonly used as an emulsifier to make salad dressing?

Egg yolks are commonly used as an emulsifier in salad dressings due to their natural properties. They contain lecithin, which is a phospholipid that helps to bind oil and water together, creating a stable mixture known as an emulsion. In the context of making dressings such as mayonnaise or vinaigrettes, egg yolks allow for a creamy texture and prevent the oil and water components from separating.

While oil and vinegar are essential components of many salad dressings, they do not function as emulsifiers on their own. Mustard, although it can act as a minor emulsifier due to its components, is not as effective as egg yolks and is often included more for flavor than for its emulsifying properties.