Natural hair dyes are available in three different categories: permanent, semi-permanent and temporary. One who has 50% gray hair has to opt for the permanent one as it offers the most extensive coverage. As this contains almost 3% peroxide, it is possible to lighten or darken the hair. The lighter the shade, the more are the toxins. Hence, it is advisable to select a color nearly equal to the natural hair color. Additionally, as the permanent type will last for four to six weeks, it will be felt essential to dye again only when the gray hair grow back again. This type also have vitamins or conditioning buffers that aids in balancing the chemicals. Natural semi-permanent and temporary colors have only 1 to 3% peroxide or ammonia. Although they have this advantage, they do not penetrate the hair shaft. Semi-permanent do not completely cover the gray hair and fade out after 12 to 16 shampoos. As temporary dyes contain only color pigment, they must be reapplied after each shampoo. There is a consensus regarding the fact that a maximum of 3% peroxide is not harmful. Only if the scalp has an allergic reaction, the dye may enter the bloodstream.