Henna hair dyes are henna-based powder hair dyes that are packed in powder form and are ready to use with just the addition of water. The advantage of using henna hair dye to color your hair rather than any other 100% chemical-based hair color is that the main ingredient is natural henna powder, which accounts for 60% of the total contents by weight. This natural henna powder, also known as mehndi, is very nurturing for hair. It is grown in fields, where leaves are plucked, ground, filtered, and then added to the product.