Some well-played profanity can make a pop song sizzle.

But few expletives in recent memory have had the potentially career- altering crackle of the one let fly by Sabrina Carpenter, a former Disney Channel star, on “Please Please Please,” her Dolly Parton-meets-Abba confection that became a surprise No. 1 hit this summer.

“Heartbreak is one thing, my ego’s another,” Carpenter flutters, before a plea to a new fling: “I beg you, don’t embarrass me, little sucker” — except instead of little sucker (the radio edit), she rhymes an unprintable four-syllable term of tongue-in-cheek endearment, dropping her voice low and lathering it in a knowing hillbilly sass.

Carpenter sells it. But she had help — a playful, foul-mouthed voice in her ear insisting that a pop star these days might as well run Dolly through a TikTok-friendly system update, or sneak a Dada phrase like “that’s that me espresso” into the cultural lexicon.

“Five years ago, I would have never thought it was OK,” said Amy Allen, the hit songwriter credited on “Please Please Please,” along with “Espresso” and every other track on Carpenter’s breakout album, “Short n’ Sweet,” which debuted atop the Billboard chart.

But Top 40, in no small part thanks to Allen, is entering a much-needed era of quirk, in which regular jolts of the unexpected are cutting through a sludge of smooth-brained content.

“Now I feel scared of generic things that sound like No. 1s,” said Allen, 32, who landed her first chart-topping hit, “Without Me” by Halsey, five years ago. “Listeners are just getting smarter and smarter now,” she added. “They want something to be odd, something to be off, something to be really catchy and unexpected about a lyric or melody. The days of really polished pop are shifting out.”

Now a fixture in pop’s A-list backrooms after years of hustling in every corner of the industry maze, Allen would know.

She has been a small-town aspirant in the coffeehouses and barrooms of Windham, Maine; a Boston College nursing student and unsuccessful contestant on “The Voice”; a Berklee College of Music transfer fronting a pop-rock band in search of a record deal; a major label prospect as a solo performer; and today, an indie singer-songwriter who recently released an eponymous debut album herself.

Along the way, Allen has become the tone- setting, behind-the-scenes pop writer of the moment, aiming to join a lineage with varying degrees of staying power, name recognition and sonic trademark that includes Max Martin, Dr. Luke, Esther Dean, Sia, The-Dream, Benny Blanco, Julia Michaels and many more who never peeked out from the shadows.

In relative anonymity, Allen wrote songs for and with Selena Gomez, Lizzo, Olivia Rodrigo, Justin Timberlake, Shawn Mendes and others, winning an album of the year Grammy for her work on “Harry’s House” by Harry Styles, and earning a nomination for songwriter of the year, for tracks with King Princess and Charli XCX, at the 2023 ceremony.

Allen’s musical fingerprints, along with her public profile, had stayed nearly unseen until they piled into an unmistakable, welcome smudge on mainstream music’s surface sheen: Starter hits for Carpenter (“Feather”) and Tate McCrae (“10:35” with Tiësto) were sugary with subtle bite. Those made room for stranger, vowel-heavy breakthroughs, as McCrae’s “Greedy,” and Carpenter’s “Espresso” and “Please Please Please,” made down-the-middle (notably white) pop fizzy again.

“She is an obvious master of pop, but her drive is to make something that’s a little bit more unique, always,” said Ethan Gruska, a songwriter and producer who has worked with Allen on her solo music. “What’s cool is that sometimes in the sphere of Top 40 pop, if that’s your instinct, people feel the need to dumb it down. But she just walks in, and she does her instinct.”

Allen’s two professional modes are separate but complementary. Inspired by the “ ’90s girls” — Sheryl Crow, Alanis Morissette, Melissa Etheridge — and also Cocteau Twins and Edie Brickell, Allen tends to write her own moody songs longhand in a notebook as poems, starting with the verse. As a hired gun, she is more economical, usually typing into an iPhone and going chorus-first (because otherwise what’s the point?).

But both kinds of collaborative songwriting often start with the same nonmusical skill: gossiping about each other’s personal lives, or in industry parlance, being “good in the room.”

Not every song that makes it out of the room is a hit. Despite her heat, the reception to Allen’s work on the comeback album from Justin Timberlake, “Everything I Thought It Was,” was tepid, and its singles failed to spark.

“Everything has to line up perfectly for something to be a hit,” Allen said. “So much of it is out of your hands.”

She said that she has probably averaged writing seven songs per week every week for the last seven years. “And we’re talking about big songs I’ve had — that’s like, what, six?” Allen said. “The batting average ain’t strong. But that’s enough to have a career.”

It also takes the pressure off Allen’s own work as an artist, a personal outlet that now allows her to “shake off the big scary pop music machine without having to compete in any way.”

As a result, her solo debut, some five years in the making, is without big hooks or quippy lyrics, opting for an alternative singer-songwriter palette, like Phoebe Bridgers doing a sparer “Folklore.”

“It’s really good for my brain to work at those two different speeds,” Allen said. “I think taking on so much of other people’s emotional things every day, all the time, I almost forget I have my own things to work through.”

Allen also is aware of the risks of representing a trend cycle, noting that, outside of Diane Warren, “there’s not a lot of women that have a ton of longevity as songwriters, which is really upsetting,” she said. “I will do everything in my power to break that stereotype.”

“I would definitely never claim to have a superpower, but if I were to say that I had something that is really helpful, it’s that my stylized thing is pretty subtle,” Allen added. “I don’t feel like there’s ever going to come a time when people are listening to a bunch of different genres on the radio, and they’re like, ‘Oh, another Amy Allen song.’ ”