On-the-scalp lighteners have a pH of

• A. About 7
• B. About 5
• C. About 9
• D. About 12

Answer: (C)

On-the-scalp lighteners work best when the product environment is alkaline, which opens the hair cuticle and allows the lightening agents to penetrate and oxidize pigment effectively. That balance of lift and scalp safety is achieved with a pH around 9. At this level, the cuticle scales lift enough to let the lightener work, but it’s not so harsh that it would be unsafe for scalp contact when used as directed.

If the pH were near 7, the environment would be too neutral to promote significant cuticle swelling and lightening. If it were around 5, the product would be mildly acidic, which actually hinders lift rather than promotes it. A pH around 12 would be very harsh and risky for scalp irritation or damage, which is why on-the-scalp formulations stay far from that level.