From Cortisol to Calm: The Physiology of Calm Breathing

“Take a deep breath.” You’ve probably heard that advice—before a big exam, a tough conversation or when you’re feeling overwhelmed. And if you’ve ever noticed that it actually helps, you’re not imagining it. Your body has a built-in system for finding calm, and breathing is the key that unlocks it.

When stress shows up, your body flips on the sympathetic nervous system, better known as the “fight-or-flight” response. Your heart races, blood pressure climbs and the stress hormone cortisol floods your system. These physiological adaptations are all useful if you need to run from danger. But the everyday stressors you face—traffic, deadlines, buzzing phones, juggling work and family—can keep that switch stuck in the “on” position, leaving you tense and drained.

That’s where slow, mindful breathing comes in. When you pause and take steady, deep breaths, you tap into the parasympathetic nervous system, often called “rest-and-digest.” It’s like hitting your body’s reset button. Your heart slows down, your muscles loosen and your brain gets the signal that it’s safe to let go and relax. Over time, practicing this kind of breathing can even help bring cortisol levels down, giving your body a chance to restore balance.

Scientists sometimes measure this shift using something called heart rate variability—the tiny, healthy variations in time between heartbeats. These normal micro-changes are a sign of resilience. A higher heart rate variability means your body can adapt to stress more easily. Slow breathing has been shown to boost heart rate variability, which is why many mindfulness and meditation practices make it a centerpiece.

The best part? You don’t need fancy tools or lots of time to feel better. Just a few minutes of slow breathing—taking about five to six breaths per minute—can help you move from cortisol to calm. The next time you catch yourself holding your breath in stress, try letting it out slowly, then breathing back in with intention. With every breath, you’re not only calming your mind, but you’re also giving your body a gentle reminder of its own strength and resilience.

Amin Mohajeri, PhD, is an educator at Northwest Vista College with a passion for science communication and making physiology accessible through teaching, writing and outreach.