What is an essential step before beginning any chemical service on hair?

Performing a strand test is essential before beginning any chemical service on hair because it helps to assess the hair's reaction to the chemicals being used. This test involves applying the chemical to a small section of hair and observing how the hair responds in terms of texture, color change, and overall integrity. By doing this, a stylist can determine the appropriate processing time and whether the hair can withstand the chemical treatment without damage. It is a precautionary measure that ensures the safety and satisfaction of the client, helping to avoid potential adverse reactions.

In contrast, trimming the hair, washing the hair, or applying protective oil, while they may be beneficial steps in a hair service, do not specifically evaluate the hair's compatibility with chemical treatments. These steps may be part of the overall preparation, but they do not provide the critical assessment that the strand test offers, making it a vital step in the chemical service process.