Coloring books are no longer solely the domain of children. Immersion in this fun, creative pastime by adults even for just 30 minutes can constitute a focused meditation that relieves stress. Doctor of Psychology Nikki Martinez, in Chicago, says that famed psychotherapist Carl Jung believed coloring helps patients release anxiety.

“It uses both sides of the brain and improves organizational and fine motor skills,” says Martinez. “After I underwent a major surgery, I was on bed rest for eight weeks, and adult coloring books were a lifesaver. They passed the time, were pretty and kept me in a constant state of calm. I devoured them.”

Publishers Weekly reported combined 2015 sales of 1.75 million copies for the 10 bestselling adult coloring books through November. This trend was years in the making, originating when parents colored with their kids and sometimes on their own. Adults around the world now join coloring book clubs, hold related parties and take coloring breaks at work. Last fall, Barnes & Noble hosted the one-day All-American Art Unwind, where customers colored and uploaded their results to Instagram and Twitter. Hallmark sent a crew of artists and calligraphers to select locations to help customers color their greeting cards.

“We scheduled a coloring session for a 55-plus community workshop,” relates Ninah Kessler, a licensed clinical social worker with the Sparks of Genius Brain Optimization Center, in Boca Raton, Florida. “People had so much fun they wouldn’t leave. It’s creative, portable and inexpensive. You never face blank paper because the lines are there; you just pick the colors. There’s no stress about possibly making mistakes.”

“Animals, jungle or floral themes, and Zen-inspired mandalas are popular. Customers like realistic, intricate drawings,” explains Idalia Farrajota, a Dallas executive with Michaels craft stores, which offers free, in-store coloring sessions and provides supplies. (Download a free sample book.) Johanna Basford, a renowned illustrator from Aberdeenshire, Scotland, is a hit with colorists, catering to their penchant for nature with Secret Garden, Enchanted Forest and her latest, Lost Ocean.

“My daughter wanted to color her life, not do generic drawings,” says Dieter Marlovics, prompting him to establish Really-Color, in Chicago. “Really-Color converts photos into coloring book pages to make individually tailored pages.”

Try these eco-tips: Sprout pencils, made with sustainable wood and fruit- and-vegetable-based dyed clay instead of lead, are topped by non-GMO seeds that can be planted when the pencil becomes short. Inktense’s water-soluble brightly colored pencils mimic pen and ink; add water for translucency. Select recycled paper books, soy crayons, watercolor paints and non-toxic markers.