I heard on Australian radio once that women spend more money on their hair than men spend on their cars. So this idea is really a marketing gimmick, although slightly sciencey.
It is my considerably uninformed opinion that hair reacts differently to different levels of humidity, etc., etc., and that some shampoos may attempt to redress this. The idea is to include a hygrometer with your shampoo packaging, with which women and hairy men can match daily humidity levels to a range of shampoos which are numbered by humidity range.
I have very little idea whether this is how hair meeks out its daily existence. Regularly having more hair than I want or need, I don't even own a comb, never mind a hygrometer.-- 4and20, Aug 06 2021 //women spend more money on their hair than men spend on their cars//
That would explain why the initial capital cost of hair is so often amortized over many monthly repayments.-- pertinax, Aug 07 2021 So glad I went bald early...-- 2 fries shy of a happy meal, Aug 07 2021 random, halfbakery