How Breathing Affects Stress and Difficult Emotions

By Anders Olsson · Updated November 2026

You’re stuck in traffic, already late for an important meeting. Or you’re at home, the kitchen is a mess, the kids are hungry and loud, the phone is ringing and the meatballs you planned for dinner are gone. A tiring email lands. Someone you love is angry with you. Notice what happens to your breathing as you read this. For most of us it speeds up a little, moves up into the chest, and maybe stops for a moment. 

Breathing and stress are tied together in both directions. When you feel stressed, your breathing changes. And when you change your breathing, especially by slowing down the breath out, you can change how stressed you feel. I have been teaching this for almost twenty years, and I still think it is one of the most useful things a person can know, because your breath is the one part of the stress response you can steer on purpose. 

What stress does to your breathing 

When something frightens us, we gasp. “Help, a tiger!” or “Oh no, that email.” It is the body waking up and getting ready to act. We do the same at the dentist, before an injection, or when we spot a spider. The breath gets stuck, the shoulders lift, and only when it’s over do we let go. There’s a reason we say “now the danger is over, we can breathe out.” 

Nerves work in a similar way. Before a speech at a wedding, breathing gets faster and moves higher up into the chest, and the uneasy feeling settles in the stomach as butterflies. Moving the breath up into the chest is a bit like running away from the feeling. The diaphragm, our main breathing muscle, moves less, and the discomfort gets more room to grow. At the same time we take the elevator up into our heads and the thoughts start racing. Stressed breathing, a busy mind and unprocessed feelings start feeding each other, and the longer that loop runs, the harder it is to step out of. 

Why so many of us breathe as if we’re always on alert 

One of the great challenges of modern life is taking in a huge number of impressions every day while keeping a breathing pattern that is calm and rhythmic. News of war and accidents, films and social media all stir up thoughts and feelings, and those change how we breathe. You can be sitting completely still on the sofa while your breathing gets ready for fight or flight. 

Over time the body learns the pattern, and the jingle of the evening news or a dramatic headline is enough to set it off. Most of this stress is mental and emotional, and there is no running or fighting to use up the extra breathing. So many of us walk around breathing a little more than our body needs, hour after hour, without ever noticing. 

What overbreathing does to carbon dioxide 

This is where carbon dioxide comes in. Your cells make CO₂ all the time, roughly a liter every four to five minutes when you are resting, and much more when you move [1]. You breathe it out as you go, which is why you breathe harder when you run than when you lie on the couch. 

When you breathe more than you need, you breathe out CO₂ faster than your body makes it, and the level in your blood drops. That is overbreathing, or hyperventilation when it becomes more pronounced. You may know the old advice to breathe into a paper bag during a panic attack or a nervous flight. The idea is to breathe back some of your own exhaled air, which holds about a hundred times more CO₂ than the air around us, and bring the level up again. Many people say they feel calmer for it. But bag breathing is not safe for everyone. Breathlessness and chest pain can come from the heart or lungs rather than from stress, and breathing into a bag lowers the oxygen you take in. If you’re not sure what’s happening, get medical help. 

Your CO₂ pressure: a mirror of how you breathe 

CO₂ in the blood is measured as a pressure, in millimeters of mercury (mmHg), the same unit we use for blood pressure. In healthy people at rest, the normal range is about 35 to 45 mmHg [1]. It shifts with every breath, which makes it a sensitive mirror of how you are breathing, and of how you are doing mentally, emotionally and physically. In my experience, people feel at their best in the upper part of that range, around 40 to 45 mmHg, which is why I think it matters so much for well-being. 

This is the guide I use in my teaching to show how CO₂, breathing and stress tend to go together. It is not a medical test, and the last column describes how people commonly feel, not a diagnosis. 

Why the exhale matters most 

When stress hits, the instinct is to take a big breath in. In my experience, the quickest way to calm stressed breathing is the opposite: let the breath out slowly. A slow, soft exhale through the nose slows down the whole rhythm. You take fewer breaths a minute, and it becomes easier not to overbreathe. 

It’s relaxation we’re after, not emptying your lungs, and it’s never a competition. I learned this again recently at a gala dinner in Spain, when a woman came to me in the middle of a panic attack. I told her to close her mouth and slightly prolong her exhale. A minute later she said she felt worse. She had been pushing every last bit of air out. Only when she found her own gentle rhythm did she start to calm down. 

Research is starting to back up this focus on the exhale. In 2023, a team at Stanford University compared five minutes a day of different breathing exercises with five minutes of mindfulness meditation, over one month [2]. The exercise that stood out was cyclic sighing, which is built around long, slow exhales. Compared with meditation, it improved mood more and lowered the participants’ breathing rate at rest. The study did not use the Relaxator or any other breathing tool, and it is one study, but it fits what I have seen in people for years. 

Three simple breathing exercises for stress 

1. Cyclic sighing. This is the exercise from the Stanford study. Breathe in through your nose, and at the top take a second short sip of air, also through the nose. Then breathe out slowly through your mouth until the breath feels complete, without forcing it. Keep going for about five minutes. If you’d rather stay with nasal breathing, breathe out slowly through your nose instead. 
2. A longer exhale through the nose. Breathe in through your nose for about four counts and out for about six. The numbers are only a guide. If it feels like you’re not getting enough air, try two counts in and two and a half out, and build from there. Two to five minutes is plenty. 
3. Hand on your belly. Put one hand on your belly and one on your chest. Let your belly move out as you breathe in and back in as you breathe out, while the hand on your chest stays almost still. Let each exhale get a little slower and quieter, and notice the short pause before the next breath comes by itself. 

If an exercise makes you feel more stressed, dizzy or short of breath, stop, breathe normally and try a gentler version another day. 

What happens in your brain when you overbreathe 

When we feel threatened, our deeper instincts take over. It’s not convenient to stop and think about whether to run left or right when a tiger attacks. But breathing also changes the brain more directly, through blood flow. 

The picture to the left shows brain activity during normal breathing, and the one to the right after one minute of hyperventilation. The more color (red, yellow, green), the more activity. Hyperventilation lowers CO₂, which narrows the blood vessels in the brain and reduces blood flow. Everyday overbreathing is far milder than this, but when it goes on hour after hour, day after day, it is worth paying attention to. 

Less CO₂, less blood to the brain 

The link between CO₂ and blood flow to the brain was mapped in the 1940s by the American researchers Seymour Kety and Carl Schmidt. Their 1946 study of hyperventilation in healthy young men was carried out under a wartime research contract with the US government [3]. They showed that overbreathing reduced blood flow to the brain. In 1948 they showed the other side: when the same kind of volunteers breathed air with 5 to 7% CO₂, blood flow to the brain rose by about 75% on average [4]. 

In 1964, Martin Reivich measured how closely brain blood flow follows CO₂ across a very wide range, in rhesus monkeys [5]. The rule of thumb that came out of this line of research is that blood flow to the brain falls by roughly 2% for every 1 mmHg drop in CO₂. Human studies point the same way. In a 2016 study, when volunteers hyperventilated until their CO₂ fell to about 30 mmHg, blood flow to the brain dropped by about 22% [6]. Push CO₂ low enough, especially together with other strain on the body such as cold water, and the drop in blood flow can be enough to make a person faint [7]. 

What surgeons and anaesthetists know about CO₂ 

Doctors use this effect deliberately. During brain surgery, the patient can be made to hyperventilate on the ventilator. The lower CO₂ narrows the blood vessels in the brain, which relaxes a tense brain and lowers the pressure inside the skull. Reviewers point out that it should only be used as a temporary measure [8]. 

Something interesting happens at the end of an operation too. Anaesthetists often hyperventilate patients to clear inhaled anaesthetic from the lungs faster. But the low CO₂ that comes with it also cuts blood flow to the brain, which slows the anaesthetic washing out. In a study at the University of Utah, keeping CO₂ up during that hyperventilation meant patients woke up and had their breathing tube removed 59% sooner on average [9]. A 2011 review went further and argued that patients may do better, with fewer complications, when CO₂ is kept higher during surgery than has traditionally been the target [10]. 

CO₂ and your stress hormones 

One study shows the stress link especially clearly. Twelve healthy medical students breathed heavily for 20 minutes on two occasions, once with normal air and once with air containing 5% CO₂ [11]. With normal air, their CO₂ fell by about 21 mmHg, and the stress hormones adrenaline and noradrenaline rose by 360% and 151%. With the CO₂-enriched air, CO₂ barely fell and the hormones stayed where they were. Same breathing, same effort; the only difference was the CO₂.  

Overbreathing affects the nerves and muscles as well. In another study, healthy volunteers who hyperventilated felt tingling in their hands, face and body, and when CO₂ fell further, their muscles began to cramp and twitch [12]. I know this one from experience. I have hyperventilated on purpose several times, and afterwards my legs and hands shook uncontrollably for several minutes, much like a Parkinson’s tremor. 

Your breath goes everywhere with you 

When stress builds up and there is no movement or calm breathing to let it out, it tends to stay in the body. The good news is that your breath is always with you. The next time traffic stops, the email lands or the kitchen is chaos, start with one slow, soft breath out. 

References 

[1] Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. 14th ed. Elsevier; 2020 

[2] Balban MY, Neri E, Kogon MM, et al. Brief structured respiration practices enhance mood and reduce physiological arousal. Cell Rep Med. 2023;4(1):100895. 

[3] Kety SS, Schmidt CF. The effects of active and passive hyperventilation on cerebral blood flow, cerebral oxygen consumption, cardiac output, and blood pressure of normal young men. J Clin Invest. 1946;25(1):107–119. 

[4] Kety SS, Schmidt CF. The effects of altered arterial tensions of carbon dioxide and oxygen on cerebral blood flow and cerebral oxygen consumption of normal young men. J Clin Invest. 1948;27(4):484–492. 

[5] Reivich M. Arterial PCO2 and cerebral hemodynamics. Am J Physiol. 1964;206:25–35. 

[6] Hartley GL, Watson CL, Ainslie PN, et al. Corticospinal excitability is associated with hypocapnia but not changes in cerebral blood flow. J Physiol. 2016;594(12):3423–3437. 

[7] Immink RV, Pott FC, Secher NH, van Lieshout JJ. Hyperventilation, cerebral perfusion, and syncope. J Appl Physiol. 2014;116(7):844–851. 

[8] Zhang Z, Guo Q, Wang E. Hyperventilation in neurological patients: from physiology to outcome evidence. Curr Opin Anaesthesiol. 2019;32(5):568–573. 

[9] Sakata DJ, Gopalakrishnan NA, Orr JA, et al. Hypercapnic hyperventilation shortens emergence time from isoflurane anesthesia. Anesth Analg. 2007;104(3):587–591. 

[10] Way M, Hill GE. Intraoperative end-tidal carbon dioxide concentrations: what is the target? Anesthesiol Res Pract. 2011;2011:271539. 

[11] Stäubli M, Vogel F, Bärtsch P, et al. Hyperventilation-induced changes of blood cell counts depend on hypocapnia. Eur J Appl Physiol Occup Physiol. 1994;69(5):402–407. 

[12] Macefield G, Burke D. Paraesthesiae and tetany induced by voluntary hyperventilation. Brain. 1991;114(Pt 1B):527–540. 

This article is for general education only and is not medical advice. Talk to your doctor before changing your breathing practice, especially if you have a medical condition.