Anxiety is both a mental and physical state of negative expectation. Mentally it is characterized by increased arousal and apprehension tortured into distressing worry, and physically by unpleasant activation of multiple body systems—all to facilitate response to an unknown danger, whether real or imagined.

The cognitive feelings of dread in anticipation of some bad outcome, and physical sensations such as jitteriness and a racing heart are designed for discomfort.

Anxiety is meant to capture attention and stimulate you to make necessary changes to protect what you care about. Occasional bouts of anxiety are natural and can even be productive. Anxiety can be considered the price we humans pay for having the ability to imagine the future.

But persistent, pervasive, or outsize anxiety can disrupt daily life, whether at school, work, or with friends—the mark of an anxiety disorder. Nearly one-third of adults in the U.S. will grapple with out-of-control anxiety at some point in their life.

Anxiety is often accompanied by depression, and the two share many symptoms and involve many of the same brain pathways. Biology can contribute to vulnerability to anxiety, as can childhood experiences such as early trauma and parenting practices such as overprotection.

Treatment is geared to keeping anxiety at manageable levels. Anxiety can be treated successfully using therapy, medication, or both. Lifestyle measures, such as regular exercise and deep-breathing, are also extremely important in controlling anxiety.