When you're looking to cover up grays, there are a few ways to do it.
You can use a semi-permanent hair color if you want the color to last for just a few shampoos (great, for example, if you want quick coverage for a party). If you're looking to make a long-term commitment, you'll want to seek out permanent color. Rather than washing out, this type of dye needs to grow out of your hair-leaving dreaded gray roots in its wake.
But somewhere in the middle lies the hair color sweet spot that many women crave. It's called demi-permanent hair color.
"This type of product will stay in the hair for 28 shampoos," explains Teca Lewellyn, a Procter & Gamble Beauty Scientist. "So, depending on how frequently you wash your hair, it will take about a month to a month and half to gently fade away."
Here's how it works: Demi-permanent hair color molecules get under the outer cuticle of the hair shaft but, unlike permanent dyes, they don't penetrate the deeper cortex. "They basically get temporarily stuck just beneath the cuticle until they are washed out," says Lewellyn. "The difference with permanent color is that the dye has to swell the cuticle to make it lift and allow the molecules to make their way into the cortex deep inside the hair shaft."
Demi-permanent may not be the answer for everyone and every hair situation, but it does have several key advantages.
It can cover up to 70 percent of your grays.
"It's a great solution for someone who's just starting to go gray and wants to experiment with color," says Lisa Evan, a colorist at Mario Russo Salon in Boston. "It gives a very natural result because the grays will take the color differently from the other strands, which means hair ends up with an almost highlighted look."
You'll never have obvious roots.
Permanent color invades the hair shaft and lodges itself there, well, permanently. So instead of fading away gradually, like demi-permanent color does, your hair stays whatever color you've dyed it, and as your hair grows, the new stuff at the roots will be the old color (or gray). With demi-permanent there's no obvious line of demarcation so you don't need to worry about touching up your roots every few weeks.
Your hair will look healthy and shiny.
"Demi-permanent is much gentler on the hair than permanent color," say Evans. That's because it doesn't open up the cuticle as much or penetrate inside the cortex of the hair shaft. "The integrity of the hair is better when the cuticle stays intact."
It can enhance and add dimension to your natural color.
Demi-permanent hair color contains no peroxide, which means it's much gentler on your strands, but also means that it won't dramatically alter the color (especially if you're hoping to go lighter than your natural shade). What it can do is warm up your color, give it more life and luster, blend away your grays and deepen your shade slightly. "It's like what happens when you polish a wood table and the brilliance of all the different shades in the wood suddenly come out," says Lewellyn. "You're enhancing what's already there."
It's hard to screw it up.
The downside of demi-permanent is that you can't make a dramatic change (it's not for you if you're goal is to take your brown strands platinum blonde). But the upside of that limitation is that very little can go wrong. Plan to stick with a color that's within one to two shades of what you've got and the result will be a beautifully enhanced version of your natural color.
You don't have to make a big commitment.
"Demi-permanent color is a great introduction to hair color," says Lewellyn. "If you're nervous about the process, this is perfect because it'll fade away within a month or so." And because you won't get obvious roots, you're not obligated to keep coloring your hair on a regular schedule.
A few demi-permanent colors to try at home:
Clairol Natural Instincts: Fortified with antioxidants, this formula helps hair defend itself against free radical damage during the coloring process. In 22 shades; $9.
L'Oréal Paris Healthy Look Crème Gloss Color: This ammonia-free formula leaves hair glossy while blending away grays. In 21 shades; $10.
Garnier HerbaShine Color Creme: Nourishing bamboo extract conditions hair while it colors. In 18 shades; $8.