How high can the pH level of a hydroxide relaxer be?

The pH level of a hydroxide relaxer can reach as high as 13.5. This elevated pH is significant because it indicates the product's strong alkaline nature, which is necessary for the relaxing process. Hydroxide relaxers work by breaking the disulfide bonds in the hair, allowing it to be straightened. The high pH level facilitates this by opening up the hair cuticle and penetrating into the cortex, where it can effectively alter the hair structure.

In the context of hair chemistry, typical pH levels for cosmetic products are around neutral (pH 7), while relaxers must be much more alkaline to be effective. Choices that reflect a lower pH do not represent the strength required for a hydroxide relaxer to work properly. Therefore, while options like 10.5, 12, and 13 might be associated with other hair products or less potent relaxer types, they do not match the maximum pH of hydroxide relaxers, which is why the highest option of 13.5 is the correct choice.