Which of the following is NOT one of the main ingredients in shampoo?

Shampoo typically contains several key ingredients that serve specific functions, and while fragrance is often added for a pleasant scent, it is not a main functional ingredient. The primary components of shampoo are water, which acts as a solvent; base detergents, which are responsible for cleansing the hair and scalp by removing dirt and oil; and moisturizers, which help to maintain hair hydration and manageability.

Fragrance serves more of an aesthetic role, enhancing the user experience rather than contributing to the fundamental cleansing or conditioning properties of the shampoo. Therefore, it is correct to identify fragrance as not being one of the main functional ingredients in shampoo compared to the other components that have vital roles in the product's performance.