Is a strand test really necessary and how should I do it?

A strand test takes only a few minutes and prevents surprises. Mix a small amount of product (or use a few drops from the sachet) and apply to a discreet section — e.g. behind the ear or at the nape — following the same timing you plan for the full application. Rinse, dry, and evaluate the tone in daylight. This shows you: (1) how strongly your current porosity absorbs the pigment, (2) whether the resulting shade matches your expectation, and (3) if any irritation occurs. It is particularly important if your hair has been bleached, highlighted, permed, or chemically straightened recently, because those processes increase porosity and can cause the colour to turn darker, cooler, or more intense than on virgin hair. If the test strand looks too strong, you can shorten the processing time, dilute with regular shampoo, or decide the shade isn't right before committing to the whole head.