NEW YORK » It starts with gloss and polish, then it’s mascara and eyeliner. To parents it might seem as if their girls are wearing makeup overnight, but sales figures show that it’s a steady progression from essentially toddlers to teens — with a surge of interest during the tween years.

But engagement with color cosmetics is waning among young women, age 18 and up, according to market research firm The NPD Group.

Young girls are becoming exposed to beauty routines earlier on — especially with all the mother-daughter bonding that’s going on at nail salons and spa birthday parties — but that excitement might be wearing off by the time older girls are establishing their own regimen, observes NPD beauty-industry analyst Karen Grant.

Overall, girls in the 13-to-17-year-old range still use more makeup than their younger sisters, but the percentage of the high-schoolers using makeup now is less than it was a few years ago, while the percentage of elementary and middle-school girls is higher.

By age 18 these young women are looking to keep their skin healthy and enhance their appearance with a handful of tried-and-true cosmetics, Grant explains, but their experimental phase is largely over.

"You’ve got girls asking, ‘Do I really need this?’" says Grant. "Maybe it’s not that exciting anymore because they’ve been using it since they were younger."

Eva Chen, beauty and health director at Teen Vogue, agrees that there’s the excitement factor that comes with literally the first blush of beauty products — but that can get old.

"A lot of tween girls think makeup is really exciting to them when they first start to wear it because it’s probably something they haven’t been allowed to do. … About 13 or 14, they feel like they’re over lip gloss. They still wear it, but that’s when they want to transition into mascara, but that’s one more step for parents to accept."

Lip product is the most used cosmetic category across all ages, says Grant, with younger girls using balm, tweens and teens using gloss and then adults wearing lipstick. But mascara is the second most important category for teenagers — replacing all the bath washes and gels that younger girls like — and women largely have a commitment to using mascara through their mid-60s.

Among 8- to 12-year-olds, 18 percent are wearing mascara on a regular basis; 47 percent of 13- to 17-year-olds; and 56 percent by age 18, according to Grant.

Compared with 2007 levels, that is an 8 percent increase in usage of mascara by tweens, while lipstick had a 5 percent increase. Both products saw a drop in usage, though, among 13- to 17-year-olds from three years ago.

"Girls see mom and they want to imitate mom," says Johanna Mooney, director of beauty products for Disney Consumer Products.

The balancing act as a manufacturer, she says, is age appropriateness. "Our view is a 10-year-old doesn’t need anything to be beautiful, but they want to be playful and aspirational. They want a little fantasy, and we want her to feel that she is feeling good."

Disney youth beauty brands are rooted in lip gloss, balm and nail polish, and then there are body mists and glitter. The dominant color is pink.

(Eye shadow, however, is sold through a partnership with MAC Cosmetics, which features products inspired by the villains of classic Disney movies.)

Mom already usually controls the purse strings for younger girls, but Mooney says a girl can get her best beauty tips from her mother.

Someone definitely needs to tell girls not to try to look too old too fast, says Teen Vogue’s Eva Chen. "Teenagers have this glow, this beauty, that adults try to reproduce." she says.

Her other tips:

» Nail polish in neon pink, green, blue — what adults would largely see as crazy shades — look fun and playful on girls.

» Red lips aren’t appropriate for a tween or even many teens.

» If you’re going to wear mascara, learn to wear it right. "You don’t want it glumpy," Chen adds.