How do I perform the patch test correctly and why is it necessary?

Permanent hair dyes contain oxidation precursors and alkalizing agents that can trigger allergic contact dermatitis, even if you have used hair color before. Sensitization can develop at any time. The patch test is the only reliable way to check before full application. To do it: wear gloves, mix a pea-sized amount of the cream dye with an equal amount of the developer (from the kit) in a non-metal bowl. Using a cotton swab, apply a thin layer to a clean, discreet area — typically behind the ear or the inner forearm. Do not cover with a bandage; let it air dry. Leave it undisturbed for 48 hours. During this time, do not wash the spot, apply other products, or expose it to heavy sweat. Check at 24 and 48 hours. Any reaction — redness, itching, burning, swelling, blistering, or a rash — means you are sensitized and must not use this product (or any oxidative dye) on your scalp. If no reaction occurs, you can proceed. Note: a negative patch test does not guarantee zero risk, but it significantly reduces the chance of a severe reaction. Repeat the test before every new box, even if the shade and brand are the same, because formulations can change.