What is a critical action you should take before starting any chemical service?

Conducting a patch test for allergies is essential before starting any chemical service because it helps to identify whether the client is allergic to the products being used. This precaution minimizes the risk of adverse reactions, which can include irritation, rashes, or more severe skin responses. By performing a patch test, you ensure the client’s safety and comfort during the chemical service, allowing you to proceed with confidence that the selected products will not cause harm.

This action is vital in a professional setting where the health and safety of the client are paramount, particularly with powerful chemical agents that are often used in hair and skin treatments. The other options, while important in their own right, do not directly address the health risks associated with chemical services. Reviewing client preferences and preparing for the appointment are beneficial for customer satisfaction and organization, but they do not mitigate potential allergic reactions as a patch test does.