The main component of hair is keratin. If we magnify the structure of hair, we can see that the surface of hair is covered with uneven scales like fish scales. The purpose of shampooing is to remove dust and excess oil from hair and scalp. The anionic surfactants in shampoo can easily cause the scales to curl up, making the hair rough, increasing friction, and easy to tangle and knot. The friction between them during combing further aggravates the damage of the scales. In order to improve this situation, we usually use the lubricating effect of oil to reduce the chance of hair damage when combing the hair. This is the reason why ancient women used osmanthus oil to comb their hair. Similarly, the role of silicone oil is precisely to adhere to the hair, making the scales flat, so that the surface of the hair becomes smoother, making the hair soft, strong, easy to comb, and shiny. This is the basic principle of two-in-one shampoo, which has both cleaning and hair conditioning effects. In addition, due to the good sealing property of silicone oil, the protective layer formed by it can also significantly maintain the stable moisture content in the hair, achieving a hair care effect. At present, the commonly used organic silicon compounds in hair care products include polydimethylsiloxane, polydimethylsiloxane alcohol, amino-terminated polydimethylsiloxane, etc. At present, the hair softening effect brought by silicone oil is still not perfectly replaced by any other oil, so more than 90% of the shampoos on the domestic market are two-in-one conditioning shampoos with silicone oil added.