Do I need a patch test and a strand test every time I use it? — TONING SEMI-PERMANENT EFFECT COLOR Bad Girl FULL MOON YELLOW 150ML

A patch test checks for allergic sensitivity. Apply a small amount behind the ear or on the inner forearm, leave for the time stated in the leaflet (usually 30–45 minutes), then watch for 48 hours. Do this before your very first application, and repeat if you’ve had any skin reactions to hair colour in the past, if you’ve changed medication, or if you have a known sensitivity to cosmetic ingredients. A strand test is different — it previews the colour result. Take a thin hidden section, apply the product exactly as you would for the full head, process for the intended time, rinse, and dry. This is essential when your base colour has shifted (new regrowth, further lightening, previous toner), when hair porosity has changed (recent bleach, chemical treatment, or heavy protein/moisture treatments), or when you want to fine-tune the processing time for a softer or stronger yellow. Skipping the strand test is the most common reason for unexpected results.