The main ingredient in mayonnaise is oil, usually vegetable oil like canola or olive oil. Mayonnaise is an emulsion primarily made by combining oil, egg yolk, vinegar or lemon juice, and spices. The egg yolk serves as an emulsifier, helping to stabilize the mixture and keep the oil from separating. The result is a thick, creamy condiment that is versatile and often used in salads, sandwiches, and dressings. Commercial mayonnaise may also contain preservatives and additional flavorings. Homemade mayonnaise is a popular option for those seeking a fresher or customized flavor profile.