Influence of Urea on the Coloring Ability of a Low-Temperature Coloring Method of Keratin Fibers Using Polyethyleneimine

The study investigated the effect of urea on the coloring ability of keratin fibers at low temperatures using polyethyleneimine (PEI) as a counter ion reagent. Human hair treated with a PEI solution containing urea showed improved coloring and color fastness to shampooing compared to hair treated with a PEI solution without urea. Optical microscopy revealed that the penetration of PEI and the dye Orange II into the hair was significantly enhanced when urea was included in the PEI solution. The researchers concluded that urea acts as a penetration accelerator for PEI, which in turn increases the penetration of Orange II, thereby improving the overall coloring ability of the hair.