Most shampoos contain sodium lauryl sulfate which some people find dries out their scalp. Baby shampoo can be smart alternative because it contains amphoteric surfactants, which are milder than SLS. The downside is that baby shampoo doesn't clean as well as shampoo with SLS. So if you use a ton of styling products, you might have to wash multiple times with baby shampoo to get it clean as you would with one lather of an SLS-based products. But that's not such a bad trade-off if your scalp is really parched.
