When performing a chemical treatment, what must be done regarding previous treatments?

When performing a chemical treatment, it is essential to assess the hair’s past chemical history to avoid damage. Hair that has been previously treated with chemicals may be weakened or altered, and applying a new treatment without understanding its history can lead to adverse effects such as breakage, over-processing, or unwanted results. Knowing the types of treatments the hair has undergone, such as coloring, perming, or straightening, allows a stylist to make informed decisions about the new treatment, including adjusting formulations or techniques to ensure the hair remains healthy and responsive.

In contrast, ignoring previous treatments could result in severe damage, while relying solely on a patch test does not provide a complete understanding of the hair’s condition. Similarly, applying a treatment without consideration of past history overlooks critical factors that contribute to the overall health and integrity of the hair. Thus, assessing the hair's chemical history is a vital step in safely and effectively performing any chemical treatment.