Box of hair dye

Photo: Sergio Kurhajec, Still Lifes: Gregor Halenda

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Demipermanent Versus Permanent Color
Demipermanent dye (often labeled "lasts through 28 shampoos" or "nonpermanent") can't lighten your hair or cover large areas of gray. It contains no ammonia and less peroxide than a permanent dye. Choose one if you want to make your color deeper or shinier, and if you don't have a lot of gray. Keep in mind: On "virgin" (colorist-speak for dye-free) hair, a demipermanent dye could wash away in as little as two weeks. If your hair is already colored (and especially if it is bleached), it will retain any color longer; even a demipermanent dye can last several months.

Permanent dye has enough peroxide to effect a more dramatic change that will last until your hair grows out. Use one if you want to lighten your hair or go more than two shades darker, or if you are more than 30 percent gray. The most exciting newcomers in this category: Garnier Olia, which includes four different oils, and Revlon Luxurious ColorSilk Buttercream, loaded with mango, shea, and coconut butters. (Garnier, $10, and Revlon, $6; drugstores)