Chemicals with sensitizing effects enter the body through certain pathways, combine with tissue proteins to form complete antigens, and stimulate immune active cells to produce sensitized lymphocytes or humoral antibodies; after a sensitization period of 1 to 2 weeks, the body’s immune response is fully developed, forming a certain number of sensitized lymphocytes or specific antibodies. When contacted (stimulated) again, the body will have a state of increased sensitivity to the chemical, which manifests in a certain abnormal form.