Have you had an adrenaline rush? Here's when it's a good thing – and when it's not.

If you've ever slammed your brakes to avoid hitting an animal darting across the road, scored the game-winning point during a ballgame, or experienced what seems like superhuman strength or speed when trying to protect yourself or a loved one, you know what a surge of adrenaline feels like.

This vital hormone affects most athletes and anyone encountering a life or death, fight-or-flight situation, but it's also been felt by people during more common and relatable experiences. Here's what adrenaline is, which circumstances and events trigger it, and why it can be crucial for your survival.

What is adrenaline?

Adrenaline, also known as epinephrine, is a hormone that's usually triggered whenever the body encounters a particularly stressful situation. This can be mental or physical stress, prompting the autonomic nervous system to provide extra power and heightened focus to help you get through the experience.

A fight or confrontation can trigger the release of adrenaline, as can experiencing a natural disaster such as a flood, fire, tornado, mudslide or earthquake. Accidents and injuries can also cause a flood of adrenaline to be released; and so can running away from a perceived danger such as a frightening human or animal coming towards you.

"Common situations like approaching an exam or even being late to an important appointment can also trigger a release of this hormone," says Dr. Massimo Testa, a sports medicine physician at Intermountain Medical Group in Utah. Other examples include when you feel pressure to win a sports game, when you experience a troubling phone call from a loved one in the hospital, or even when you are faced with the prospect of public speaking. Adrenaline can also be released in response to an illness or infection.

What does adrenaline do to the body?

Most commonly activated in the hypothalamus area of the brain, adrenaline gets released through neurotransmitters that send a signal down to the adrenal glands, which sit atop each kidney. "Adrenaline can also be released by some nerve cells in the central nervous system where it acts as a chemical messenger to promote communication between other cells and target tissues," explains Gordon Lynch, a professor of anatomy and physiology and the director of the Centre for Muscle Research at the University of Melbourne.

When a lot of this hormone is released, you may experience what's sometimes called an "adrenaline rush." During this, your pupils will dilate and you may experience a heightened state of focus and quickened reflexes. "You may also feel diminished fear and an increased heart rate and breathing to promote blood flow to working muscles," says Lynch. This blood flow subsequently allows muscles "to contract with more force and power than what we might normally need to perform most of the tasks of everyday life," he explains, which is why some people report feeling stronger than normal in hyper-stressful situations.

And when the release of adrenaline is associated with trauma or an injury, it often also masks pain by inhibiting signaling pathways throughout the body. A typical example of this is when two people get in a fist fight and don't experience much pain until the fight is over. "The evolutionary benefit of this is that, in order to survive the situation, we can complete a task before feeling the pain," explains Testa.

Is adrenaline a good or bad thing?

Though it's defined as a "stress" hormone, a release of adrenaline is usually a good thing as it's meant to aid in critical circumstances. Adrenaline can also be useful as a medical intervention. "Adrenaline is a medication that we give when patients are experiencing severe illness related to sepsis, hypotension, cardiac arrest and anaphylaxis," says Dr. Melissa Leber, the director of the sports medicine emergency department at Mount Sinai in New York City. It's used in such circumstances, "to ramp up the body's ability to fight by increasing one's heart rate, cardiac output, and blood pressure," she explains.

But adrenaline isn't our body's only stress hormone, and experiencing too much of any stress response can be harmful over time. Stress hormones like adrenaline are essential in some situations, but experiencing them too often can have long-term consequences such as high blood pressure, obesity, diabetes, sleep disorders and heart disease. "Adrenaline can cause anxiety as well," says Testa.

What does stress do to the body? It might be worse than what you realize.

Because of this, he says it's best to manage one's stress levels by getting enough sleep, eating right, exercising, and planning plenty of time to relax and connect with others.

This article originally appeared on USA TODAY: What is adrenaline? Understand how it impacts your body, brain