Daniel wants to know if social media is actually bad for you — or if that is just something adults say.

The answer turns out to be more interesting and more complicated than most headlines suggest.

Many social media apps are designed to keep you engaged and coming back. Notifications pull you back. Infinite scroll removes a natural stopping point. And unpredictable social feedback — sometimes a post gets lots of likes, sometimes nothing — can make checking especially compelling. Psychologists have studied similar patterns of intermittent reward in many kinds of behavior, including gambling. The comparison does not mean scrolling and gambling are identical. But both involve uncertainty about when the next rewarding thing will appear.

Brain-imaging studies have found that social feedback such as receiving likes can engage reward-r ...