An obsession is a thought, idea, or interest that takes over someone's mind so completely that it becomes hard to think about anything else. When something becomes an obsession, it dominates your attention like a song stuck on repeat in your head, except you can't make it stop even when you want to.

People can be obsessed with all sorts of things. A student might develop an obsession with solving a particular puzzle, thinking about it during meals, dreaming about it at night, and rushing to work on it every free moment. A scientist might have an obsession with understanding how hurricanes form, spending years studying storm patterns. Sometimes obsessions are productive: Marie Curie's obsession with understanding radioactivity led to groundbreaking discoveries.

But obsessions can also become unhealthy. Someone obsessed with video games might neglect homework, friends, and sleep. An obsession with what others think can make someone anxious and miserable. The key difference between a passion and an obsession is control. A passion energizes you and fits into a balanced life. An obsession controls you, crowding out other important things.

When psychologists talk about obsessive behavior, they often mean thoughts that cause distress or anxiety. Someone might obsessively worry about germs, checking and rechecking whether they've washed their hands. That kind of obsession goes beyond intense interest: it interferes with living a normal, happy life.