Question by Darla: How does the pH of the bleaching solution affect its ability to lighten hair?
how does pH from the bleach stop your hain from lightening?
Answer by Kate H
The pH from the bleach does NOT stop your hair from lightening.
Actually, colouring hair is a 2-step process. First you must open the cuticle (outer layer) of the hair shaft with an alkaline chemical, and then the colour is deposited/removed by the dye reacting with the hair’s cortex (inner portion of the shaft). Most people don’t realise that even if they are dying their hair darker than its natural colour, the original hair colour is ALWAYS removed.
Ammonia (often) is the alkaline chemical that opens the cuticle and allows the hair color to penetrate the cortex of the hair. It also acts as a catalyst when the permanent hair color comes together with the peroxide (or whatever bleaching/oxidizing agent is used).
Actually, the pH of ammonia is about 12 (quite alkaline), so without the ammonia the peroxide (generally closer to neutral) would not be able to bleach your hair as effectively.
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