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.
Know when to go lighter or darker. The rule is as follows: For permanent dye, choose a color a smidge darker than what you want because of the strong developer, says Ionato. With semipermanent dye, however, err on the lighter side of the color you're looking to achieve. "Semipermanent formulas don't have a developer, meaning they get darker and darker the longer you leave them in your hair," says Ionato. "It's safer to choose a color that's a bit lighter from the get_go."