But before going under the needle, experts suggest the super-moist skin inside the mouth is not the ideal spot for a tattoo, no matter how tempting its apparent cool factor may seem.
Cyrus pulled down her lower lip to show off her bright yellow and black "sad kitty" Emoji tattoo — which also sports a royal blue teardrop — in a recent photo posted on her official Instagram page.
How long the "Wrecking Ball" singer's tat will last, given the turnover of cells lining the inner lip and the constant bath of saliva, is anybody's guess.
At the New Tribe Tattoo shop in Toronto, ink artists get regular requests for inner lip tattoos, said manager Eric Gaudet.
"I'd say at least a couple of people ask about it per week and I'd say maybe a couple per month actually get it done," Gaudet said Tuesday.
"We do technically do them, but we usually try and talk people out of them — not because of a health reason, but just to let them know that they don't heal like normal tattoos and most of them, they'll just kind of fall out. They won't last."
Even so, dermatologist Dr. Julia Carroll believes that tattooing the inside of the lip — which is made up of blood-rich mucosal cells — could pose a risk of infection.
The warm, moist human mouth is an ideal environment for bacteria, and it can harbour hundreds of different species of bacteria at once. That means there could be up to a million individual bacteria swirling around the teeth, gums, tongue and lips at any given time.
"If you look at bites across different species, the bite from a human is one of the dirtiest ones you can get," said Carroll, who practises at Compass Dermatology in Toronto.
"The other thing about mouth tattoos is they need to be repeated for touchups because the type of cells that live in the mouth turn over quite quickly, so the tattoos wear out," she said, adding that those touchups again expose a person to potential infection.
Initially, eating highly acidic foods like vinegar-containing salad dressings, tomatoes or citrus fruits will likely irritate the tattooed area, although that will pass, Carroll said.
More serious reactions could be an allergy to the dyes used to colour a tattoo, which could cause painful swelling. Although relatively rare, it's also possible to develop a foreign body reaction, in which the immune system tries to get rid of the inks, resulting in granulomas — small, painful, swollen balls under the skin that can worsen over time and are difficult to eliminate.
With its nerve-rich flesh, the inner lip is one of the most painful areas to have tattooed, Gaudet confirmed.
And it's a body part that poses a challenge for ink artists because of the texture of the skin and the need for the client to hold their bottom lip open with as little movement as possible.
Gaudet said clients are told upfront that unlike designs done on arms, legs or chests, for instance, the shop can't guarantee the inner lip tattoo will last.
"We're going to do our best to make sure that it does, but we cannot guarantee it," he said, adding that a mouth tattoo costs $80 plus tax, with a maximum single free touchup.
"We want them to be educated and informed about what they're getting into. We don't want them to feel ripped off if the tattoo comes out."
Gaudet said most people get a single word needled into their inside lip, then coloured with the same inks used for regular skin tats. "We just tell them you don't have a choice of font. We just do it as simply as we can and then we just hope for the best."
While some remain permanently, often a lip tattoo will last only weeks to months.
A search of online tattoo blogs shows photos of people rolling back their lips to show tattooed symbols or words, such as "Rock.N.Roll," "Fixation," "Bite Me" and various unprintable expletives. One man has his inside upper lip tricked out with a moustache.
Two years ago, pop singer Ke$ha tweeted a photo of herself exposing the tattooed message “SUCK IT” on her inner lower lip.
"People just do it because it's kind of funny," said Gaudet. "An inner lip tattoo, it's just kind of more of a jokey tattoo for a lot of people. I get it. It is pretty funny."
Amusing it may be, but Carroll has mixed feelings about the placement of such tattoos.
"As a mom, I could look at that and sort of say, 'Well, at least when you're going to get a job, you're not going to be seeing it," she mused.
"But I think more importantly, as a physician, although I think generally tattoos are pretty safe these days, I think kids need to be aware there is a risk of infection and there's going to be a lot of pain and swelling straight away."
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