Over the last few decades, we have heard more and more people in business talking about multitasking. We even have a whole generation dedicated to multitasking. That means they have a dozen tabs open on their laptop, while updating their Facebook page, listening to Taylor Swift, while they are supposed to be doing their homework.

Unfortunately, more and more studies show that multitasking is a bad idea. It can hurt your brain, your career, and change your personality. Travis Bradberry writing in Forbes puts it this way: “You’ve likely heard that multitasking is problematic, but new studies show that it kills your performance and may even damage your brain.” They found that even people who felt they have a special gift for multitasking did worse on performance tests than those who focused on a single thing at a time.

Studies also found that multitasking lowers your IQ. One study at the University of London found that participants who multitasked during cognitive tasks experienced IQ score declines that were similar to what they’d expect if they had smoked marijuana and stayed up all night. Another study at the University of Sussex compared the amount of time people spend on multiple devices to MRI scans of their brains. They found that high multitaskers have less brain density in a region of the brain responsible for empathy as well as cognitive and emotional control.

An article by Drake Baer in Fast Company documented how multitasking rewires our brains. In previous commentaries, I have talked about how our brains are plastic. The technical term is neuroplasticity. If we train our brains to multitask, we are training them to think differently. Clifford Nash at Stanford University has found that the more you multitask, the less you’re able to learn, concentrate, or be nice to people. He has found that: “People who multitask all the time can’t filter out irrelevancy. They can’t manage a working memory. They’re chronically distracted.”

Multitasking is the latest fad, but I hope you can see why many researchers have concluded that multitasking is bad idea.