When you say 'this could be popular saying' are you meaning that it may be wrong because it's popular?

I'd be curious to know your results, in any case. I've had mixed outcomes from conventional (commercial shampoos) and have also been trying to identify causal factors (worse in winter, especially after a few days of wearing a beanie, worse when I'm staying near a high-pollution area, etc). It's all anecdata, but OTOH not beyond our abilities to thoughtfully analyse.