Open up TikTok and there’s a good chance you’ll be confronted by a teenager in the bathroom.

Most home bathrooms are well lit and have nice, bright acoustics. Unlike the kitchen, living room or even bedroom, bathrooms are private spaces, where parents and siblings are trained to not barge in.

It’s almost inevitable that they would become the perfect stage set for the dramatic entrances, exits, skits, dances and story times of TikTok, the short-form social video app that has grown wildly popular in the last year.

Videos shot in the bathroom consistently outperform those shot elsewhere, many creators say. They call it “the bathroom effect.” Milli2nd, a 21-year-old music producer known for performing with a mirrored pyramid over his head, said he has shot the same video in multiple settings and the bathroom versions win. “Ones I’ve done in the bathroom get much more views,” he said.

Colby Schnacky, 23, said he has shot 12 bathroom videos, each of which has over 500,000 views. He tried other things, like shooting in selfie mode, but bathroom videos do so well that he continues to post from there.

Evan Alberto, 21, estimated that nearly half of his videos are filmed in a bathroom. “When you see someone walk into the bathroom, it’s like a cliffhanger but in the beginning,” he said. “You open the door, you point the camera at the mirror, it’s a hook.”

“I usually film in the bathroom instead of my room because the bathroom lighting works really well,” said Jalen Harris, 17.

Daniel Mitch, 20, said he thinks it’s the full body aspect of bathroom videos that make them appealing. “Being able to see how someone’s holding the phone or their full body language when they’re in the mirror, you can do a lot with that to make your video funnier in general,” he said. He estimated that half of his TikTok videos have been filmed in the bathroom.

“In typically quirky TikTok fashion, the bathroom mirror has been a consistent reflection of the community’s unique ability to make the ordinary, be it washing your hands or flipping on a light switch, low-key extraordinary,” said Gregory Justice, the head of content operations at TikTok.

Staring Through the Mirror

While TikTok as a social media behemoth is fairly new — its start in the United States was in 2018 — people have been using the bathroom mirror to create internet content for years.

Cringey mirror selfies are all over Snapchat and Instagram; some of the most iconic Vines like “shower time and Diesel jeans” or “Hi welcome to Chili’s” were shot in bathrooms.

But if YouTube documented a generation of American bedrooms, TikTok makes the American bathroom inescapable. Tomisin Adeleye, 17, a TikTok creator who uses bathroom videos to discuss topics including racism, dating, Rihanna and why some guys get their ears pierced, estimated that about 30 percent of his recommended feed was bathroom videos. “It’s definitely a standard format,” he said.

Jacob Pace, the chief executive of Flighthouse, a marketing agency and media brand, said: “They’re everywhere.”

According to Vanessa Flaherty, the executive vice president of talent at Digital Brand Architects, a social influencer talent management agency, when selfies first cropped up, “the reason those were so appealing is that they appeared very off the cuff and not staged.”

“The videos in front of the bathroom mirror have that same quality,” she said. “They’re not staged, there isn’t production value.”

The bathroom mirror alone plays a key role in many of TikTok’s most popular memes. One recurring joke includes a person filming in the bathroom mirror over days or months, making some type of transformation (first day of school to last day of school, for instance).

Another leverages a camera trick to show a person or group seemingly falling through the bathroom floor repeatedly. There are many, many, many, many, many more. (There is even an entire genre of memes that incorporate the bathroom sink.)

When the influencer James Charles recently announced he was looking for a boyfriend on TikTok, he did it from the bathroom. The bathroom at the Hype House, a mansion in Los Angeles where young influencers collaborate, is the group’s most popular place to film.

“Spending a lot of time on TikTok, and it seems that knowing how to film yourself speaking with a cellphone in a bathroom mirror is a new skill to be mastered,” Jon-Stephen Stansel, a digital marketer, tweeted. “It’s like a stand-up learning to work a microphone, it’s part of the craft.”

Mr. Alberto sees a similarity with musicians. “How a nice guitar plays a big part in what they do,” he said. “The bathroom mirror is like that for me.”

The bathroom is simultaneously more personal but less revealing than the bedroom. If you film in your bedroom, people are going to judge you on what stuff you keep around or what posters you have on your walls, said Joshua King, 14. It can feel too revealing.

The bathroom is neutral, even uniform, but still feels intimate. “It’s quite awkward to film a TikTok, so the bathroom is an easier place to do that,” he said.

Even restaurant, hotel and high school bathrooms are common settings. Brian Feldman, a technology writer, noted that the high school bathroom serves as “a sterile, blank canvas onto which video makers can project themselves and share their private moments with the rest of the world.”

Finding the Perfect Bathroom

The most common bathroom portrayed on TikTok is the type found in millions of suburban middle-class homes. The aesthetic in general is Home Depot: a neutral colored sink and low countertop with a massive fixed mirror above, with composite doors and air-conditioning vents.

But not every bathroom makes a great TikTok bathroom. Bathrooms with busy wallpaper or yellow lights can be problematic.

And TikToks shot in messy bathrooms don’t perform as well. Ryan Ketelhut, 17, said that shooting TikToks has made him clean his bathroom at home more often.

“I keep it cleaner now because I am in there making TikToks,” he said. “You need to have all your stuff and all your candles and whatever else not strewn everywhere. I had to clean up a little bit before I filmed my last TikTok. I usually have clothes laying in the bathroom. I cleaned the sink out a little with a Clorox wipe and I sprayed down the mirror so it’s not as grimy.”

Some TikTokers said it’s the first thing they look for when choosing a place to live. “I should be moving to L.A. in the next month or so,” Mr. Alberto said. “A hundred percent I’m going to make sure that I like the setting of the bathroom. It’s a silly thing, but the videos on my channel that get the most views are in the bathroom.”

Finding the right bathroom, particularly one with light walls and a giant mirror, is also playing a role in Mr. Mitch’s Los Angeles apartment search. “I’m definitely going to check out the bathroom and see how it is, because the appearance can have a lot of impact on my videos,” he said.

Kids that are too young to live alone must work with the bathrooms they’ve got. “I see a lot of school restrooms, a lot of personal restrooms — it’s a thing to go into the gas station restroom and use the sound, like, ‘I’m in the ghetto,’” said Ethan Ramirez, 17. (He was referring to a popular meme on the app in which the phrase “I’m in the ghetto” is the refrain.)

“In my school it’s become a big problem that people are filming TikToks in the bathroom,” he said.

The bathroom is so often being used for filming that it can be awkward for kids who have to use it for its intended functions. Recently Mr. Ramirez was in one of the stalls when a group of kids came in and immediately began filming TikToks. “I was like, ‘I am in here,’” he said. They continued to film.