Chemistry in Your Day : Bleached Blonde

Have you ever bleached your hair? Most home kits for hair bleaching contain hydrogen peroxide (H₂O₂), an excellent oxidizing agent. When applied to hair, hydrogen peroxide oxidizes melanin, the dark pigment that gives hair colour. Once melanin is oxidized, it no longer imparts a dark colour to hair, leaving the hair with the familiar bleached look. 


Hydrogen peroxide also oxidizes other components of hair. For example, protein molecules in hair contain - SH group called thiols. Hydrogen peroxide oxidizes these thiol groups to sulfonic acid groups (SO₃H). The oxidation of thiol groups to sulfonic acid groups causes changes in the proteins that compose hair, making the hair more brittle and easier to tangle. Consequently, people with heavily bleached hair must use conditioners, which contain compounds that form thin, lubricating coatings on individual hair shafts. These coatings prevent tangling and make hair softer and more manageable.


The following is a reaction of hydrogen peroxide with an alkene:


H₂O₂ + C₂H_{4 ->} C₂H₄O + H₂O


Taken from Chemistry: A Molecular Approach by Nivaldo J. Tro

Other Readings:

• Redox: Fundamentals, Processes and Applications
• Introduction to the High Temperature Oxidation of Metals
• Lab-Aids Introduction to Oxidation-Reduction Kit