Shampoo is meant to clean your hair and scalp of dirt, oil, and hair products. While it's common to think of shampoo as a hair cleansing agent, it's more important to consider your scalp when choosing a shampoo. My rule of thumb is this: shampoo should be chosen based on your scalp condition; conditioner should be used to treat your hair. This way, if your scalp is oily and your ends are dry (which is a common problem), choose shampoo that is best suited for an oily scalp and a conditioner that is best suited to hydrate your dry ends. Why? Because like your face, treating the oil conditions on your scalp (whether it's dry, oily, or somewhere in the middle) begins with proper cleansing. Introducing the proper moisture back into your hair can be accomplished by selecting the right conditioner.