Demi-permanent hair dye is less damaging than permanent hair dye because it uses a smaller amount of hydrogen peroxide (1-2%) and minimum amounts of ammonia and ethanolamine or even skips them altogether. This means that demi-permanent hair dyes do not penetrate the hair deeply, which makes them less damaging. However, it is important to note that many hair dyes contain ingredients that can irritate the skin or cause an allergic reaction, such as paraphenylenediamine (PPD), which is a known irritant and allergen. Some hair dyes also contain harmful chemicals that are linked to an array of health harms, including cancer, scalp and skin irritation, and allergic reactions. Therefore, it is important to read the ingredients list and follow the manufacturers instructions, including doing a patch test before every hair color application.