A Guide to Using Pure Castile Soap as Natural Shampoo Commercial shampoo can be irritating and harmful to some people, especially those with sensitive scalps or skin. This is because commercial shampoos may contain harsh, drying, and harmful ingredients, such as sulfates, parabens, synthetic fragrances, and artificial colors. If you are looking for a safe and effective shampoo, you may want to consider buying organic castile soap from Singapore.