What must be done before applying a new hair dye to a client?

Before applying a new hair dye to a client, it is essential to perform a patch test. A patch test determines whether the client may have an allergic reaction to the hair dye ingredients. This is crucial for the safety of the client since some individuals can experience allergic dermatitis, which can manifest as redness, itching, or swelling at the site where the dye is applied. The patch test usually involves applying a small amount of the dye on a discreet area of the skin, often behind the ear or on the inner arm, and waiting for a specified period—typically 24 to 48 hours—to observe for any adverse reactions.

While performing a strand test is also a valuable practice for checking how the hair will react to the dye, it does not specifically assess the client’s skin sensitivity to the dye. Shampooing the hair can help remove buildup before dyeing, but it is not a prerequisite for dye application. Obtaining a signed consent form is also important in professional practice, as it serves as documentation of the client's approval and acknowledgment of the procedure; however, it does not directly address allergies or sensitivities to the dye. Thus, conducting a patch test is the most critical step to ensure the client's safety before proceeding with the application of hair dye.