Even if you have used other hair colors in the past, a skin test needs to be performed. To perform the skin allergy test: Carefully unscrew the cap from the developer and open the tube of color mix. With a cotton swab, mix a dab of color and a dab of developer. Place that on a clean area on your forearm at the rear of your wrist. Replace caps securely on your hair color and developer. Do not wash off for 48 hours. If irritation, swelling or severe itching occurs, please do not continue to use your color. This result indicates that you are allergic to this product. See your physician before reattempting. If there are no adverse effects from the test site, proceed with the coloring application.