bleaching

Bleaching refers to a chemical process that reduces or removes color from materials or objects, yielding a whiter appearance. The term encompasses industrial operations applied to textiles, paper, and wood, as well as cosmetic procedures that lighten hair or teeth. Bleaching works mainly by oxidation: reactive species break down chromophores, the molecular structures responsible for color, or physically remove pigments from the substrate.

Common bleaching agents include chlorine-based compounds such as sodium hypochlorite, hydrogen peroxide, chlorine dioxide, and various peracids. The choice of agent and conditions (pH, temperature, duration) influence efficiency and potential damage to the material.

In textiles and paper, bleaching aims to produce whiteness and uniformity, often following pulping or dyeing. Household bleaching uses solutions of sodium hypochlorite or hydrogen peroxide to remove stains. Hair bleaching employs alkaline catalysts and peroxide to oxidize melanin in the cortex, resulting in lighter hair; results depend on hair type and existing color, and damage risk is higher with improper use. Dental bleaching uses peroxide-based gels applied in-office or at home to oxidize stain compounds in enamel and dentin; outcomes vary and tooth sensitivity can occur.

Safety and environmental considerations are central: bleaches can irritate skin, eyes, and the respiratory tract; mixing some agents incorrectly can generate hazardous gases; disposal and wastewater treatment require care to minimize environmental impact.

A historical note: modern bleaching has evolved from chlorine-based methods to include peroxide- and oxygen-based systems that reduce harmful byproducts.