The Good Housekeeping Institute breaks down why: "Other than henna, any commercially available hair dye store_bought for home use or found in salons uses chemical actives for them to work," says Birnur Aral, Ph.D., Director of the Good Housekeeping Institute's Health, Beauty and Environmental Sciences Lab. "By and large, these chemicals are synthesized substances." Even when the packaging claims to be all_natural, organic or chemical_free which is literally impossible because everything, including organic things, are made of chemicals that could basically be an outright lie. This is because the FDA can't do anything about the use of these terms regarding cosmetics.
Keep in mind that even a brand so committed to natural formulas must rely on some synthetic ingredients in order for the hair color used in its salons to work. "The remaining 4% of the ingredients are of synthetic content which are the colorants, dyes and preservatives," Mejia_Montane explains. "It is unavoidable to include synthetic ingredients in professional hair color because all of the colorants and dyes used in permanent and demi_permanent hair color are synthetic. These are the ingredients that create hair color via the oxidation process."