There are Facebook pages devoted to adult colorers. There are coloring clubs. People who motivate themselves to pay off debt by coloring. Game of Thrones is making a coloring book.

What this means: Coloring is now a normal adult activity.

Thanks largely to a recent wave of publicity over the release of illustrator Johanna Basford’s second coloring book, coloring books as a whole have been enjoying their 15 minutes of fame.

Taking over bestseller lists

Actually, they’ve been enjoying a lot more than 15 minutes: Basford’s book, Enchanted Forest, is #9 on the UK Amazon best selling books page as of June 28, and has been in the top 100 list for 113 days. Her first adult coloring book, Secret Garden, was published two years ago but it sits close behind Enchanted Forest in the number 11 spot, and it’s been in the top 100 for 211 days.

And Basford isn’t alone at the top of the book charts: In the UK there’s an animal-themed coloring book in the number three slot, an anti-stress coloring book at number four and a “relaxing” one at 15. The latter two highlight a theme among some of these books, which capitalize on the idea that adults need a reason to color. In the US, Basford Secret Garden is joined in Amazon’s US top 20 list by one that claims “stress-relieving patterns” and another that says “Coloring time is calming time!”

It’s good for you

There seems to have been, before now, some embarrassment attached to the notion that an adult might enjoy an activity as childish as coloring. Publishers behind these books have skirted that by marketing these books with health-based justifications and scientific evidence about the benefits of coloring. “Selling the anti-stress angle gave people permission to enjoy something they might have felt was quite childish,” one publisher’s spokeswoman told the Guardian in April.

Many adult colorists have latched onto the idea that coloring promotes mindfulness, and can help reduce stress. They are right, judging by the latest expert thinking. Though there aren’t studies specifically on the benefits of adult coloring, play is important for both adults and children. Coloring can act as a de-stressor, art therapist Saba Harouni tells Quartz.

“You’re giving your brain some some space and something to focus on that’s meditative, that’s containing,”

These coloring books can act as a reset button for adults who are moving too quickly from one responsibility to the next, or trying to do them all at once. The repetitive motion of coloring can be both cathartic and meditative, and you can focus on filling in the lines on the page. ”You’re giving your brain some some space and something to focus on that’s meditative, that’s containing,” Harouni says.

If you need more reasons, psychologists also told the Huffington Post that coloring allows for creativity and can invoke positive childhood memories.

Coloring books have been marketed to adults for a while, but they’ve only recently hit it big. Artist Jenean Morrison has self-published six adult coloring books on Amazon, full of intricate designs, since 2012, she tells Quartz. She actually got the idea when she came upon an old coloring book from her childhood, a 1970s book that was design-based rather than populated with pictures of “cows or princesses,” she says. Those designs still appealed to her.

Morrison isn’t in the top 100 on Amazon anymore (she was for about eight weeks in the US, earlier this year), but she too has seen the benefits of the adult coloring craze. In all of last year, she sold 15,414 books on Amazon. This year, in half the time, she has sold 43,420.

The sharp increase took her by surprise, she says. “Have they wanted to do this all along, they just were afraid to tell their friends?” She thinks people certainly do it for fun, but she also gets letters that demonstrate the positive effects of coloring books—a prison recently requested a batch for inmates who use them for therapy and stress release, and recovering surgery patients have told her that coloring her books is the only way they manage to stay put.

You don’t actually have to pay money to color, by the way. One of the Facebook groups devoted to adult colorers, called Coloring Pages for Adults, regularly posts designs that you can print out and play with at your leisure.

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The featured image in this post is courtesy of Flickr user Eugene Kim.