On any given day, Melissa Barrett, 33, slathers on more than half a dozen facial products — and that’s not including makeup. Every morning she uses a face wash with toner, an antiaging serum, an eye cream, and a moisturizer. At night, she adds a face peel, a vitamin C serum, and an intense moisturizer.

“I don’t feel burdened by my skin care regime, I feel like it’s necessary,” the Manhattan resident said. “I kind of like having a skin care line and a process.”

But recently, at the suggestion of a Bergdorf Goodman cosmetics saleswoman, she added yet another product to her already complicated beauty regimen, one that fits somewhere in between skin care and cosmetics: a foundation primer. “The salesperson convinced me that it would make my foundation last longer and remain fresh,” Ms. Barrett said.

In the quest for complexion perfection, many women are now incorporating a post-cleanse, premakeup prep step to their routines, turning to products such as face, lip, and eye primers as a way to boost the effectiveness of the makeup they already wear. Such primers are designed to even out skin tone and make color cosmetics last longer; eyeshadow primers can also prevent creasing, while lip primers combat bleeding and feathering.

Although consumer research firms such as Euromonitor International and NPD don’t individually track sales of primers, such prep steps “are definitely increasingly popular products,” a senior research analyst for Euromonitor, Virginia Lee, said. A search for primers on Sephora.com turned up 54 products, several of them from the cosmetics brand Smashbox. At the department store Henri Bendel, foundation primers have become big business in the last five years.

“It’s one of those word-of-mouth things that’s started to build in popularity,” the senior vice president and general merchandising manager for Henri Bendel, Claudia Lucas, said. As such, she added, “they’ve become an integral part of how we sell foundation to our customers.”

Ms. Lucas estimates that 75% of the color brands Henri Bendel carries now feature foundation primers in their lines, but said that makeup artists such as Laura Mercier, Paula Dorf, and Trish McEvoy (who all have their own cosmetics lines) “were real pioneers” of primers. “They had the experience and knowhow to recognize there was a need for this kind of product,” she said.

The trend isn’t limited to prestige brands, however: Maybelline New York’s new Superstay Silky Foundation, which launched in January, is a two-in-one product that contains both color and a coverage extending primer in one package.

Ms. McEvoy, who introduced her first foundation primer, Even Skin, about four years ago and introduced her second, Beauty Booster, six months ago, thinks primers are more popular because women have gotten smarter about applying makeup.

“People are looking to touch up less,” she said. “The extra prep steps that you do — foundation primer, eye base, even lip primer — only take a couple of seconds, but every single step after is going to last longer.”

Despite the promised benefits, primers aren’t necessarily for everyone, according to Dr. Jordana Gilman, an assistant clinical professor of dermatology at Mt. Sinai School of Medicine in New York. Dr. Gilman, who said she has seen a gradual increase of patients using primers, warned that women “need to be careful not to fall into a marketing trap” and to make sure that the products they are using are appropriate for their skin.

Dr. Gilman isn’t against primers per se. “But [it’s] another layer of something on the skin,” she said. While adding another product to one’s daily beauty routine isn’t problematic on its own, the dermatologist explained that skin issues could arise when people use products that aren’t right for their skin type or use them inconsistently.

Some primers actually appear to reduce the number of steps in a beauty regimen by doing double duty. Ms. McEvoy’s Beauty Booster is billed not just as a primer, but also as a moisturizer and a mask. Smashbox’s Photo Finish Foundation Primer is available in several formulas, including ones with antiaging ingredients and bronzer. Nars makes a primer with SPF 20. (Multitasking claims aside, both Dr. Gilman and a Montclair, N.J.–based dermatologist, Dr. Jeanine Downie, recommend using a separate sunscreen product in order to ensure adequate protection. With a stand-alone sunscreen, “you put more on and get broader coverage,” Dr. Downie said.)

Ms. Barrett, who began using her face primer three months ago, admitted that she isn’t “100% convinced that it really does anything.” But she’s not giving up on it yet. After all, what’s one more step?