Everything You Need to Know Before You Dye Your Hair Yourself

Do:

Touch Up Roots Only: Meaning the fresh, untouched regrowth. Repeatedly dyeing mid-lengths and ends (the oldest, most damaged areas) will leave hair dry, brittle, and too dark from color buildup. Use conditioner to shield those areas.

Work in Sections: Clip up one in front of each ear and two in the back, then let one down at a time for an even application.

Buy Two Boxes for Long or Thick Hair: You can’t go to the drugstore if you run out mid-app.

Don't:

Start With Unwashed Hair: Product residue can reduce absorption. Shampoo before.

Try to Go Too Light: Any more than three to five shades needs a professional, says George Papanikolas, a Matrix colorist.

Skip the Patch Test: “Dye a few strands to check the tone and how they absorb color,” says Daniel Moon, consulting colorist for L’Oréal Paris.

Wash Your Hair Immediately: Wait at least 48 hours. “It gives the cuticle time to close so color won’t wash out,” says Meri Kate O’Connor, colorist at Eva Scrivo Salon in NYC.

How to Decode the Dye Box

Permanent: This dye opens the cuticle (hair’s outer layer), pushing color deep into the cortex. It lasts indefinitely (but can fade or oxidize).The downside: Stronger chemicals make it more damaging.

Demi-Permanent: It deposits color to the cuticle (but not the cortex) and "fades in six weeks," says James Corbett, Clairol color director.

Semi-Permanent: "This sits on top, staining hair," says O’Connor. It can refresh tones or darken hair and washes out in 4 to 12 shampoos.

Bleach: The fastest—and most damaging—way to lighten. Peroxide lifts the cuticle, then bleach diffuses your pigments. The longer it’s on, the brighter you’ll be.

Gloss: It refreshes oxidized or faded color and adjusts tones with a sheer, light deposit of color, says Papanikolas.

Nude: The latest color craze (seen on Cara Delevingne) combines both warm and cool tones. It works on just about everyone, says Papanikolas.

Cool/Ashy: A color with green, blue, or violet undertones. It absorbs light rather than reflects it, so while you’ll see less red, “your hair may lack luster,” says Marko Tomassetti, colorist at Serge Normant at John Frieda Salon.

Warm/Golden: A color with an undertone of red, orange, or yellow. While too much warmth equals brassy, “warm shades reflect tons of light,” says Tomassetti.

This article was originally published as "Know-It-All Guide to Pro Hair Color—at Home" in the April 2017 issue of Cosmopolitan. Click here to subscribe to the digital edition.