1) Sulfates in shampoos combine with the sebum on your scalp and eliminate essential residue and oil that keeps your scalp and hair roots moisturised. Eventually, they make your hair brittle and frizzy and won't bring back your original hair colour as promised.
2) The foam that occurs when you rinse your hair while shampooing happens due to the presence of a chemical called sodium lauryl sulfate. It has toxic effects on your hair follicles and makes them dry over time. Even if you use a hair dye to hide the greying of your hair, this chemical will fade that colour away in no time.
3) Most shampoos contain sodium chloride to make their consistency thicker. If you have a sensitive scalp, sodium chloride is a strict no-no for your hair. It will make your scalp itchy and dry and eventually lead to unwanted hair fall.
4) Does your shampoo say that it contains synthetic colours? If yes, it's a red flag and you should avoid using it. Synthetic colours in shampoo are obtained from coal-tar and petroleum that don't provide long-lasting colouring effect on your hair. Moreover, they make your hair dry and brittle after a few weeks.
With shampoos and dyes failing to provide the desired result of reversing grey hair, you may feel that there's no other option left.
Well, there is.