What is the main purpose of a patch test before applying hair dye?

The main purpose of a patch test before applying hair dye is to check for potential allergic reactions. This test is crucial because it helps identify if a client will have an adverse reaction to the chemicals present in the dye, particularly those that can cause skin irritation or allergic responses. By applying a small amount of the dye to a discreet area of the skin, typically behind the ear or on the inside of the elbow, a stylist can monitor the area for any signs of redness, itching, or swelling. Conducting this test at least 48 hours before the full application provides essential protection for the client, ensuring their safety and comfort during the dyeing process.

The other options relate to important aspects of using hair dye but do not address the primary health concern that the patch test is designed to mitigate. Determining application technique, assessing color result, and evaluating hair texture are all relevant to the overall hair coloring process but are secondary to ensuring that the dye is safe for the client's skin.