Harmful effects of frequent hair coloring on human body include: making hair dry and rough, hair loss, allergy, inducing blood system diseases and impairing skin immune function. 1. Hair dryness, roughness and hair loss: Hair dyes can color hair because they destroy the structure of the hair itself, thus coloring it, and frequent dyeing of hair will make it dry and rough, and increase its brittleness. In addition, hair dyes also damage the structure of hair follicles, causing hair loss. 2. Allergy: Hair dyes contain a lot of organic ingredients, which can easily cause allergy. The symptoms include itchy skin, red spots on the body, and in severe cases, swelling of the scalp. 3. Blood system diseases: hair dyes contain a lot of p-phenylenediamine and hydrogen peroxide, which will not only damage the skin, but also may be absorbed into the blood through the skin, and then flow to the bone marrow, destroying the hematopoietic cells of the bone marrow and inducing blood system diseases. 4. Low skin immune function: silver nitrate and benzene-containing organic compounds in hair dyes may cause low skin immune function, and the skin’s ability to resist external stimuli decreases, and frequent dyeing of hair may increase the prevalence of skin diseases.