Everyday Chemistry: The Bleaching of Hair

• Many home-bleaching kits contain hydrogen peroxide (H2O2), an oxidizing agent.
• Hydrogen peroxide oxidizes melanin, the dark pigment that gives hair color.
• Once melanin is oxidized, it no longer imparts a dark color to hair, leaving the hair with the familiar bleached look.
• Hydrogen peroxide also oxidizes the protein molecules in hair that contain —SH groups called thiols.
• Thiols are normally slippery. Hydrogen peroxide oxidizes these thiol groups to sulfonic acid groups, —SO3H. Sulfonic acid groups are stickier, causing bleached hair to tangle more easily.