“Brain games” have become a popular way to stay sharp as you age.

Whether it’s a daily crossword, a book of Sudoku puzzles, or a virtual brain-training program (part of a $12 billion industry), these games are often marketed—and widely believed—to help preserve cognitive skills like memory, problem-solving, and processing speed.

But do they really work—and if so, which ones are most effective? Here’s what science says. As you age, your brain starts to shrink. Research suggests that after age 40, brain volume and weight decrease by 5% each decade, and the rate accelerates after age 70.

But the shrinkage isn’t uniform. The prefrontal cortex—the region responsible for decision making, planning, and complex thought—tends to shrink more than any other area of the brain. The hippocampus, which is essential for memory and learning, also experiences significant decline. As a result, older adults often experience cognitive difficulties, such as trouble multitasking, paying attention, and recalling words and names.

When it comes to your brain, there’s some truth to the saying “use it or lose it,” experts said. “Your brain is an organ, and if you’re not using all parts of it, especially in aging, disease, and poor health, it might start shrinking,” Ian McDonough, PhD, an associate professor of psychology at Binghamton University, told Health. Brain games are thought to train neural connections, just like working out builds muscle. It’s true that the more you play any game, the better you get at it—and the more you develop the specific skills needed to win, such as planning or problem-solving. The question is whether those skills can actually transfer to real life.

“If I do Tetris a lot, I’m going to get better at Tetris. Does that mean I’ll be better able to remember my groceries?” McDonough said. Most of the time, the skills don’t transfer, he said. Experts were especially skeptical about computer brain-training programs, such as Lumosity and BrainHQ, which claim to improve everything from memory to IQ.78 A 2016 research review found that brain-training games may improve performance on specific tasks, but there’s little evidence that they enhance everyday cognition. “It sounds like a magic bullet. There’s just no magic,” Elizabeth A.L. Stine-Morrow, PhD, a professor emerita in the Department of Educational Psychology and Beckman Institute at the University of Illinois Urbana-Champaign, told Health.

“They’re just these decontextualized laboratory tasks,” Stine-Morrow added. “Everyday life offers much more stimulation than these brain-training games.” Despite their skepticism, experts agree there’s no reason to abandon your daily brain games—especially if you enjoy them.