Hair coloring proucts generally fall into four categories: temporary, semipermanent, deposit only/demi, and permanent. All these hair color products, except for temporary color, suggest a patch test before application to determine if the client is allergic to the product. "Hair lightening," referred to as "bleaching" or "decolorizing," is a chemical process involving the diffusion of the natural color pigment or artificial color from the hair. This process is central to both permanent hair color and hair lighteners.