Impact of oxidative hair coloring and bleaching on hair fiber properties

Introduction. Hair coloring is a major segment of the cosmetics market, with 51% of Brazilian households using hair dyes. Given their widespread use and potential adverse effects on fiber integrity, it is important to understand the structural and chemical impacts of bleaching and coloring treatments on hair. Objective. To evaluate and compare the effects of professional and at-home hair coloring treatments on hair fiber properties—combability, color, and protein loss—in dark-brown virgin hair strands. Methods. Straight, virgin dark-brown hair strands (15 cm, 3.0 g) were subjected to eight treatments combining bleaching powders, hydrogen peroxide (10–40 vol), and permanent dyes ranging from blonde to dark brown. Combability was assessed using a Diastron® MTT 175. Color was evaluated by diffuse reflectance spectrophotometry, and protein loss was quantified as albumin equivalents. Results and Conclusions. Bleaching produced the greatest color difference (DE* = 65.2 ± 1.8) and increased combing force by 46.6%, whereas treatments including coloration improved combability by up to 46.5%. All treatments caused substantial protein loss (5.1–16.6 mg albumin equivalents/g hair) compared with control strands (0.7 mg albumin equivalents/g hair). Bleaching compromised hair structural integrity, while dye formulations containing emulsifiers partially mitigated damage and improved combability; however, both processes led to considerable keratin degradation.