There are usually no fixed signs before the onset of hair coloring, but hair coloring may increase the chance of cancer development. There are no signs before the onset of cancer caused by hair coloring, and most of the early cancer manifestations are not obvious. Hair dyes contain many chemicals, such as dioxin, which is a strong carcinogen, and long-term exposure may lead to gene mutation and cancer. People with chronic diseases, autoimmune diseases or allergies should avoid hair coloring. For example, if skin cancer occurs, repeated localized ulcers, infections, breakouts or bleeding, and wounds that do not heal may occur, and prompt medical treatment is required upon discovery.