| Henna dye can last just as long as permanent hair color until the hair grows out. However, these dyes require allergy tests because it can cause moderate or severe skin reactions, although it's rare. If you haven't used henna before, be sure to do a patch before applying the dye to your hair. The patch test involves putting a dab of hair dye behind the ear or inside the elbow, leaving it there for two days, and looking for itching, burning, redness, or other reactions. |