What must a cosmetologist do before using a new chemical product on a client?

Before using a new chemical product on a client, conducting a patch test to check for allergies is essential for ensuring client safety. A patch test involves applying a small amount of the product to a discreet area of the client’s skin and monitoring for any adverse reactions, such as redness, swelling, or irritation, over the next 24 to 48 hours. This practice helps to identify any allergic reactions or sensitivities that the client may have to the ingredients in the product, thereby minimizing the risk of serious allergic responses during the actual service.

While reading the product’s instructions thoroughly is important and notifying the client of potential side effects is a good practice, neither directly ensures the client's safety in relation to personal allergies to the product. Applying the product to oneself first does not guarantee that it will be safe for the client since individual reactions can vary significantly. Conducting a patch test is a proactive measure that helps protect the health and wellbeing of the client.