Root touch-ups have come a long way since older formulas that could look cakey, feel crusty or cover only a small area," Aral says. "The modern formulas look and feel more natural." Here, GH Beauty Lab and hair color pro guidelines for finding your ideal match: Sprays and powders are best for camouflaging large areas of regrowth and the scalp, as they can deliver high pigment load with a single application, Aral says. Demi-permanent color blends gray roots into your dyed color and appears more translucent, Ikeda notes, with results lasting four to eight weeks. Semi- and demi-permanent color are less commonly used for root touch-ups because the regrowth may still be visible. Permanent color fully covers regrowth and grays and also has the ability to lift your natural hair color. It lasts four to six weeks. In the Beauty Lab's permanent root touch-up products test, scientists dyed human hair samples in brown, red and blonde shades mixed with gray, then assessed initial gray hair coverage and shine using the Chromameter machine. Next, each dye's color retention was gauged by putting the dyed hair samples through 20 wash and dry cycles using the Swatch Wash Station and four hours of UVA light exposure with the Q-Lab QUV Accelerated Weathering Tester. Final Chromameter readings where taken, then Beauty Lab scientists assessed color change in the dyed hair samples to determine how well each resisted fading.

The GH Beauty Lab evaluates root touch-up products both in the Lab using technical instruments and on consumer or expert testers. Temporary root touch-up products are assessed by testers on factors including ease of application, color coverage (including gray) and blending, transferring and staining, flaking, lasting power and ease of removal. Root touch-ups are a cost-effective way to help seamlessly blend your roots into the rest of your hair. "These products, in formulas like sprays, powders, creams and dyes, are applied directly to roots and act as hair color extenders," says Good Housekeeping Institute Beauty, Health & Sustainability Lab Senior Chemist Danusia Wnek. Temporary root touch-ups "can be applied in a moment’s notice, and are often compact enough for a purse or bag," she says. There are also permanent, semi-permanent and demi-permanent root touch-up products that consist of hair dye created to be applied specifically to roots.