Final answer:
Brushing hair helps remove dirt, debris, tangles, and product buildup, but not scalp oil (sebum). To effectively remove sebum, shampooing is necessary due to its formulation containing surfactants that trap and rinse away oil.
Step-by-step explanation:
Brushing the hair before a scalp treatment helps remove many impurities such as dirt and debris, tangles and knots, and product buildup. However, brushing typically does not remove scalp oil, also known as sebum. Shampooing is necessary to effectively cleanse the hair of sebum, which naturally conditions and waterproofs the hair and skin but can contribute to a greasy appearance and acne if not properly managed. Regular use of shampoo, typically formulated with surfactants like sodium lauryl sulfate, helps to trap and remove sebum without over-stripping the hair, making it an essential step in hair and scalp care.
While brushing can help distribute scalp oil along the hair shaft providing some natural conditioning, for a thorough removal of excess oil and preventing buildup, a proper shampoo with the ability to create micelles is necessary. The action of shampoo's surfactants helps encapsulate oil particles, making it easier to rinse them away, thereby cleaning the hair and scalp effectively.