Substances in hair dyes may sensitize the scalp. In addition, hair dyes may also be harmful to the human body if they contain carcinogenic substances or excessive heavy metals in their ingredients. Some people with allergies may be allergic to substances in hair dyes, such as phenylenediamine, after using hair dyes, which may cause tingling and burning sensation on the scalp and small red rashes, and prolonged use may lead to damage to the scalp, which may then become infected and lead to folliculitis and other diseases, which should be discontinued or replaced by the use of hair dyes. In addition, hair dyes may contain some carcinogenic substances or heavy metals, long-term use will not only have a strong stimulating effect on the hair, resulting in lack of luster, hair loss, but also may cause the scalp to absorb these toxic substances to the body, damage to the liver and kidney function, and even cause leukemia and other diseases. If you need to use hair dyes, please check the ingredients in detail and try to avoid getting hair dyes on your scalp.