Tapping fingernails triggering goosebumps, whispers sending shivers down the spine: the brain-tingling world of ASMR has the internet clamoring for sounds that feel good.

The auditory-sensory phenomenon sees people experience waves of calm and pleasurable quivers of the mind often referred to as "brain orgasms" -- and it's emerging from the depths of the web into the pop culture mainstream as a means to relax.

ASMR, short for autonomous sensory meridian response, has become a full-fledged internet sensation, with YouTube creators notching millions of views for clips featuring stimuli -- soft whispers into a microphone, long nails tapping, noodle slurping -- to set off a prickle at the back of the neck.

"It's that moment where all the hair on your body stands up," said Bianca Hammonds, who works on the ASMR channel for the US music outlet Fuse.

"You kind of feel your body vibrate," she told AFP. "It's like this zen moment."

A beer commercial aired during the Super Bowl recently showcased ASMR, with actress Zoe Kravitz whispering, drumming her fingers against a bottle and pouring the liquid to release a gentle fizz.

But it's largely hip hop's tastemakers who have ushered it onto the scene, with rap stars making their own ASMR videos or even integrating its techniques into their songs.

"I love ASMR," Cardi B whispers during a clip she made with fashion magazine W.

"My husband thinks it's very strange and weird that I watch ASMR every single day to go to bed," the rap queen continues in hushed tones, lightly tapping and caressing the mike with her signature extra-long nail extensions.

- ASMR-rap symbiosis -

The subgenre's velvety qualities have some people dubbing ASMR sexual: China began censoring it last year, saying web users were releasing porn under its veil.

But experts have likened ASMR to massage or yoga, saying it's not inherently sexual, but can be suggestive.

Just five percent of participants reported using it for arousal in a 2015 British survey, while a 2018 study from the University of Sheffield found that unlike sex, ASMR actually reduces the heart rate.

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Predominately popular among teenagers and 20-somethings, ASMR's online fanbase began forming around 2010.

"I always knew I liked people to whisper in my ear. I just didn't know the term for it," said Cedrick Williams, an ASMR video creator from Mobile, Alabama.

"When I started doing it, no one really knew what it was," said the 27-year-old, who started his ASMR YouTube channel in 2017 and says the side gig makes about $100 per month.

"It's blowing up -- now everybody's doing it," according to Williams, who listens to ASMR to alleviate anxiety and insomnia.

When making his own videos, he favors whispering rap songs.

"With hip hop you can have a very diverse sound with your voice, so if you can master whispering -- in ASMR it works very well."

Craig Richard, an ASMR researcher at Virginia's Shenandoah University, said the relationship also works in reverse, saying there's a "clear trend of integration of ASMR into hip hop."

- 'Mind massage' -

21 Savage -- the British-born, Atlanta-based rapper whose immigration travails recently launched him into the global spotlight -- has a song titled "asmr," and also introduced whispering onto his track with producer Metro Boomin, "Don't Come Out The House."

Richard says the ASMR-rap marriage makes sense: "With hip hop and rap there can be incorporation of spoken word, which allows the ability to whisper and still be within their musical genre."

Plus, he said, rappers aim to stay fresh: "they're reflecting back to their younger fan base because they drive the trends."

Despite its growing association with the genre, rap is not the only style drawing inspiration from ASMR: Canadian electronica DJ deadmau5 sampled a whispering YouTube star for the song "Terrors In My Head."

For Hammonds, starting an ASMR series at music-focused Fuse was a "no brainer."

"We wanted to tap into a subculture," she said of their project entitled "Mind Massage."

"It focuses on sound, and we focus on music culture, so we wanted to see what we could do there," said Hammonds, who owes ASMR's popularity to its meditative qualities.

"We're in this world of constant distraction and overshare," she said. "To actually listen in on something that's making you relax -- literally focusing on the sounds -- I think that's why it's really popular."

Rappers are eager to do a segment, she said, because "they're respecting these subcultures as a way to bloom."

So far acclaimed trap producer Zaytoven along with rappers T-Pain and Wiz Khalifa are among those to appear on Fuse ASMR clips -- but there's one eccentric rap legend Hammonds is aiming for.

"I can't wait for us to get Snoop Dogg," she said.