Fluorescent whitening agents Whitening objects are actually an optical effect that does not replace chemical bleaching. If the fiber containing colored impurities is treated with an optical brightener without chemical bleaching, the whitening effect is not obtained. Chemical bleaching agents are actually oxidizing agents or reducing agents, which use their oxidation or reduction to fading colored impurities in the fibers. The essence is that the chemical bonds (generally unsaturated bonds) in the impurity molecules are broken into colorless by oxidation. The small molecule loses its color by being reduced to a saturated bond.

　　Chemical bleaching can damage fibrous tissue to varying degrees. The whitening of the fluorescent whitening agent does not cause damage to the fibrous tissue. However, fluorescent whitening agents are quite sensitive to ultraviolet light, and if the treated article is exposed to sunlight for a long period of time, its whiteness is lowered by the gradual destruction of the fluorescent whitening agent molecules. The common feature of fluorescent whitening agents and fluorescent dyes is that both can fluoresce, except that the former absorbs invisible ultraviolet light and emits visible fluorescence with a shorter wavelength; while the latter absorbs visible light and emits visible fluorescence with longer wavelengths.