Most shampoo manufacturers focus on the extra ingredients in their products, things like volumizing additives, fragrances and exotic botanical essences or extracts.
Too many shampoo products contain ingredients that may irritate sensitive skin and scalp, for those with eczema or seborrheic dermatitis - allergic reactions and skin rash are too common.
When it comes to ingredients the two worst offenders are SLS (Sodium Lauryl Sulfate) and CAPB (Cocamidopropyl Betaine) - both have been shown to cause skin irritation and CAPB has a reputation as a potential allergen.
If you have sensitive skin or a sensitive scalp make sure to check your shampoo label to avoid these two ingredients, along with other unnecessary additives and harsh chemicals.