What do you do? Go for a moisturising shampoo.
Moisturising shampoos, are a less harmful alternative to regular sulfate shampoos. They clean your hair without stripping it completely of its natural oils.
A moisturising shampoo is gentle enough to use weekly. Of course, if you have cheap and easy access to a good quality sulfate free shampoo, then by all means go for that! However, if you don't want to pay the premium you could pick a moisturising shampoo.
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How To Shop for a Sulfate Free Shampoo: Cocamidopropyl Betaine and Decyl Glucoside