Most shampoos are not hair friendly
As both our hair and scalp are acidic, it is best to use hair care products that are of similar acidity level.
A review was done on 123 international brand shampoos. It was found that the pH level (acidity level) of over 60% of the shampoos are not optimal for hair and scalp. So basically, if you select a shampoo at random from a web shop or store, the chance that you get a hair friendly shampoo is only 40%.
有研究對123個國際品牌洗髮水進行了審查。發現超過 60% 的洗髮水的 pH 值（酸度）不是頭髮和頭皮的最佳選擇。所以基本上，如果你從網店或商店隨機選擇一種洗髮水，你得到適合頭髮的洗髮水的機會只有40%。
As mentioned in our earlier posts, shampoo with higher pH will swell and lift the outer layer of hair cuticle, leaving the inner hair structure vulnerable to damage. It would also increase the amount of time required for the scalp's acid mantle to restore itself. That means your scalp is more prone to dryness and infections.
Source : "The Shampoo pH can Affect the Hair: Myth or Reality?" International Journal of Trichology, 2014