California Cosmetology Practice Exam 2026 – 400 Free Practice Questions to Pass the Exam

Overlapping product on already treated hair can cause scalp irritation during a chemical service primarily due to the increased sensitivity of the hair and scalp in those areas. When a chemical product is reapplied to hair that has already been treated, the hair cuticle can become more porous and less able to withstand additional chemical exposure. This can lead to over-processing, which not only damages the hair but can also cause irritation to the scalp. The harshness of the chemicals can aggravate the scalp's skin, leading to discomfort, redness, or even chemical burns.

In contrast, non-approved hair products may lead to adverse reactions, but the focus here is on the interaction of products applied to hair that has already been treated. Not applying enough product might fail to achieve the desired results, but it is less likely to lead to immediate irritation. Using products that are too high in pH can also be damaging, but the specific risk linked to overlapping with previously treated hair is more pronounced in regards to scalp irritation during a chemical service.