What you find in most shampoos is Sodium Laureth/Lauryl Sulphate (SLS). It's the ingredient that strips the scalp of the oil- tenside. However, apparently that chemical is quite aggressive.
It's also used (of course in bigger quantity) in floor cleaning products.
A milder, natural alternative is something like Coco Glucoside (no chemist- there might be a different term).
The idea of nopoo is that instead of stripping of the scalp of all the oil- that is needed to...