Have a read about SLS, it's sodium lauryl/laureth sulfate https://bloggingerika.hubpages.com/hub/Is-SLS-Bad-For-You. It's used as the foaming agent in things like toothpaste, shampoo, face washes etc its probably first on the list of ingredients after water on most your products, it's also used as a chemical floor cleaner and engine degreaser as it basically strips the top layer of things, it's listed as an irritant! Most people use SLS every day with no problems and lucky them that's fine, but if you have sensitive skin/scalp the process of stripping all the oils and aggravating the skin can make conditions like dandruff, acne, dermatitis worse especially as your skin will try to compensate for what it removes, ive recently switched to a SLS free shampoo, the one I chose i found on amazon if you search 'Argan oil SLS free' but theres plenty out there, it's all natural so it's not going to aggregate anything, I also use an SLS free face wash and my skin is so so much better as its not being upset by any products! Hth