What allergy-test steps should I follow before using this permanent dye?

Even if you have colored your hair before, sensitization can develop at any time. Open the color cream and developer bottles. Using a non-metallic teaspoon, mix approximately 1 cm of color cream with an equal amount of developer in a small plastic dish. With a cotton bud, apply a pea-sized drop to a clean, discreet area — the skin behind the ear or the inner forearm works well. Let it dry and leave it uncovered for 48 hours. Do not wash, cover, or apply other products on that spot. Watch for redness, itching, swelling, burning, or blistering. If any of these appear, rinse immediately with plenty of water and do not use the product. If the test area stays calm, you can proceed with the full application. Note: this test only screens for contact allergy to the dye intermediates (such as PPD or PTD); it does not guarantee you will not experience scalp irritation from the alkaline developer. If you have a known sensitivity to oxidative dyes, a history of severe reactions, or a scalp condition like eczema or psoriasis, consult a dermatologist before coloring.