In common parlance, people use “stress” and “anxiety” interchangeably. Even mental health organizations tend to lump the two together.

The Anxiety and Depression Association of America (ADAA), for example, has resources to help people manage “anxiety and stress.” But it takes some digging on the ADAA site to find an explanation for how the two differ, and that explanation is also unhelpfully brief: “Stress is a response to a threat in a situation. Anxiety is a reaction to the stress.”

Even among psychiatrists and psychologists, “there is not widespread agreement on how to contrast these two concepts,” says Richard Maddock, MD, a professor of psychiatry and behavioral sciences at the University of California, Davis. While both stress and anxiety can produce similar responses in the human body — responses that are associated with a range of health conditions, including depression and heart disease — they’re not the same, Maddock says.

Stress is a broader concept than anxiety, he says. Stress can be either psychological or physical and either good or bad. Maddock points to exercise as a form of physical stress that, while challenging to the body, can result in positive changes. Similarly, some people relish the short-term stress associated with public performances or other pressure-packed situations.

Anxiety, on the other hand, is always psychologically driven and always unpleasant, he says. Anxiety has three essential components. The first is a perception of some sort of threat — either real or imagined. (That threat could be a turbulent flight or just the prospect of a turbulent flight.) The second component, Maddock says, is “a sense that it is necessary to respond to the threat or to do something about it.” The third is “a sense that one lacks the capacity to adequately respond to the threat.” This feeling of helplessness is important; when people feel prepared to meet a challenge or threat, that sense of preparedness tends to quell anxiety.

Another helpful way to differentiate between the two is to think of stress as something that is triggered by an external challenge, while anxiety is born in the mind. “Stress is something that pulls the body or mind away from homeostasis, or its regular set point,” says Gerard Sanacora, PhD, MD, a professor of psychiatry at the Yale School of Medicine. That something could be a raging toddler, a crisis at work, or a bear that has just wandered into your campsite. Stress can trigger a racing heart, sweaty palms, jitteriness, or other short-lived physiological responses that are intended to help a person respond to these sorts of external challenges.

“It’s hard to make people’s lives have fewer stressful events. But you can change the way they perceive those events, which can reduce anxiety.”

Anxiety, meanwhile, is the mind and body’s persistent response to — or anticipation of — an external threat or stressor, Sanacora says. If you’re concerned that a crisis could arise at work or a bear could wander into your campsite, you’re experiencing anxiety, not stress. “You can have anxiety without any external event,” Sanacora says. This is a big deal, because even if the external threat never materializes, anxiety can trigger all the same internal responses that are associated with stress-related health issues. Anxiety can make your heart rate speed up, your palms sweat, and your mind race with worry. It can also flood your blood with stress-related hormones like adrenaline and cortisol.

“In many ways, anxiety is the experiential component of stress, and it’s dependent on how a person perceives that external source of stress,” Sanacora says. If a teacher surprises two students with a pop quiz, the external source of stress — the quiz — is the same for both. But if one of those students has studied the quiz material and the other has not — or if one cares more about their grades than the other — the anxiety each person experiences will be quite different.

Why does any of this matter? “It’s hard to make people’s lives have fewer stressful events,” Sanacora says. “But you can change the way they perceive those events, which can reduce anxiety.” Lowering anxiety helps limit the hormonal, immune, and nervous system reactions that are associated with an increased risk for stress-related diseases, he says. And recognizing the psychological underpinnings of anxiety can help people learn to sidestep or calm the unhealthy internal processes it triggers. This is true whether a person is grappling with ordinary anxiety or an anxiety disorder.

One way to temper anxiety is to confront its source. For example, someone who feels anxious about speaking in public could enroll in an improv class. Or a person with a fear of dogs could spend time with a friendly pooch. Exposure therapy of this sort has proved effective in treating a range of anxiety disorders. And it’s just one type of cognitive behavioral therapy, which is broadly defined as teaching a person to think about the source of their anxiety in new and less worrisome ways.

“One of the main points here is that all people experience stress, but not all stress produces anxiety,” Sanacora says. Anxiety is the fuel that keeps the fires of stress burning. Take away the fuel, and the fire burns out.