What test is used to determine how hair will react to hair color?

The strand test is essential for assessing how hair will react to hair color before applying it to the entire head. This test involves taking a small section of hair and applying the hair color to it to observe the results. By doing this, you can determine not only how the hair's texture and porosity will affect the final color but also how well the hair will absorb the dye. The strand test allows for adjustments in the formulation or application process if needed and helps prevent unexpected results, such as excessive lightening or uneven color.

Other testing methods, while useful in their own contexts, do not specifically evaluate the hair's reaction to color. A patch test, for instance, is primarily a safety measure to check for allergic reactions to hair dye rather than its effectiveness on the hair itself. The swatch test, though it may refer to testing color samples, does not typically address the individual hair characteristics that affect color results. The comb test does not exist as a recognized method for determining hair color reaction.