Holding your breath triggers a cascade of real physiological changes, some of which carry genuine health and performance benefits while others pose serious risks. The outcome depends almost entirely on how long you hold, how often, and under what conditions. A brief breath hold during a yoga class and a five-minute competitive apnea attempt are completely different acts as far as your body is concerned. The science on this topic has grown considerably in recent years, driven by interest in freediving, breathing-based training methods, and even radiation therapy.
What Your Body Does the Moment You Stop Breathing
When you voluntarily stop breathing, your body activates what physiologists call the mammalian diving response. This is a reflex shared across mammals, from seals to humans, that prioritizes oxygen conservation. Your heart rate drops (bradycardia), blood vessels in your extremities constrict to redirect blood toward your brain and heart, and stress hormones like catecholamines surge into your bloodstream.1PubMed Central. The mammalian diving response: an enigmatic reflex to preserve life?2PubMed. The human diving response, its function, and its control Face immersion in cold water amplifies the response, but it kicks in to some degree with any voluntary breath hold on dry land.
Meanwhile, carbon dioxide builds up in your blood while oxygen levels fall. Chemoreceptors detect this shift and generate an increasingly uncomfortable urge to breathe. Eventually you hit what researchers call the breaking point, an involuntary respiratory act that overrides your willpower and forces you to inhale, preventing loss of consciousness.3PubMed Central. Factors Affecting Voluntary Breath-Holding Duration and Breaking Point in Young Adults The sensation of discomfort you feel before that point comes largely from tension building in the respiratory muscles, which are contracting against a closed airway. It is not oxygen starvation causing the distress initially; it is carbon dioxide accumulation and the muscular struggle itself.4Respiration Physiology. The control of breath holding
The Spleen Squeeze and What It Does to Your Blood
One of the more surprising responses to breath holding happens in your spleen. Within seconds of an apnea, the spleen contracts, squeezing out a reserve of red blood cells into your circulation. In one study, spleen volume shrank by roughly 20% during the first breath hold, and the contraction occurred in both trained divers and untrained individuals.5PubMed. Spleen volume and blood flow response to repeated breath-hold apneas This dump of extra red blood cells temporarily increases hemoglobin concentration, boosting the blood’s oxygen-carrying capacity at exactly the moment you need it most.6PubMed Central. Apnoea as a novel method to improve exercise performance: A current state of the literature
Researchers have confirmed this by comparing people who still have their spleens with those who have had them surgically removed. In people with spleens, serial breath holds raised hematocrit by about 6% and hemoglobin concentration by about 3%, with both returning to baseline within ten minutes after stopping. In splenectomized subjects, neither value changed at all.7PubMed. Selected contribution: role of spleen emptying in prolonging apneas in humans The spleen contraction appears to be a built-in part of the diving response and may help explain why repeated apneas gradually become easier as a session progresses.
Repeated breath holds also stimulate erythropoietin (EPO), the hormone that tells your bone marrow to produce more red blood cells. In one study, serial apneas raised circulating EPO concentrations by an average of 24% compared to baseline, and a control day without apneas showed no such change.8European Journal of Applied Physiology. Increased erythropoietin concentration after repeated apneas in humans This is the same hormone that endurance athletes have infamously injected to gain a competitive edge, yet here the body produces it naturally in response to the brief oxygen deprivation of breath holding.
Can Breath Holding Improve Athletic Performance?
The EPO and hemoglobin findings have caught the attention of sports scientists. Repeated-sprint training combined with prolonged breath holds at the end of exhalation (a technique abbreviated RSH-VHL) has been tested in several sport-specific trials, and the results are promising. In semiprofessional soccer players, this method nearly doubled the maximum number of sprints athletes could complete in a repeated-sprint test, while a control group training without breath holds improved far less.9International Journal of Sports Physiology and Performance. Additional Benefits of Repeated-Sprint Training With Prolonged End-Expiratory Breath Holding for Improving Repeated-Sprint Ability in Semiprofessional Soccer Players The breath-hold group’s arterial oxygen saturation dropped to around 78% during training, compared to 97% in the normal-breathing group, creating a potent hypoxic stimulus without altitude chambers or special equipment.
A similar study in elite judo athletes found that breath-hold training improved their ability to sustain power output in later repetitions of a high-intensity test. The percentage decrement across the test dropped, meaning the athletes faded less as they fatigued.10PubMed Central. Hypoventilation training including maximal end-expiratory breath holding improves the ability to repeat high-intensity efforts in elite judo athletes Beyond the blood changes, long-term breath-hold training has been associated with better tolerance of high carbon dioxide levels, mental resilience, and favorable adaptations in the cardiovascular and cerebrovascular systems.11PubMed Central. The application of breath-holding in sports: physiological effects, challenges, and future directions
A practical note: these studies used structured protocols with specific breath-hold durations, recovery intervals, and supervision. They were not testing casual or random breath holding. The benefits appear to come from repeated, controlled exposures that push oxygen saturation low enough to trigger adaptive responses but not so low or so long that they cause harm.
Immune and Inflammatory Effects
One of the most talked-about applications of breath holding is the Wim Hof Method, which combines cyclic hyperventilation, deliberate cold exposure, and breath retention. A landmark study tested whether people trained in this method could voluntarily influence their immune response when injected with a bacterial endotoxin (a substance that normally triggers flu-like symptoms). The trained group showed dramatically higher epinephrine levels, a rapid rise in the anti-inflammatory cytokine IL-10, and lower levels of several pro-inflammatory markers. They also reported fewer flu-like symptoms than the untrained control group.12PubMed Central. Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans
A systematic review of the broader Wim Hof Method literature concluded that the technique may reduce inflammation in both healthy and non-healthy participants through this epinephrine-driven pathway.13PubMed Central. Does the Wim Hof Method have a beneficial impact on physiological and psychological outcomes in healthy and non-healthy participants? A systematic review The complication in interpreting these results is that the method bundles breath holding with hyperventilation and cold exposure. Isolating which component deserves the credit is difficult, and researchers have been cautious about attributing the immune effects to breath retention alone.
Breath Holding in Cancer Treatment
One of the most concrete clinical applications of breath holding has nothing to do with fitness or wellness. In radiation therapy for left-sided breast cancer, doctors routinely ask patients to hold a deep breath during treatment, a technique called deep inspiration breath hold (DIBH). When you inhale deeply and hold, your diaphragm flattens and your lungs expand, physically pulling the heart away from the chest wall and out of the radiation field.14PubMed Central. Deep Inspiration Breath Hold: Techniques and Advantages for Cardiac Sparing During Breast Cancer Irradiation
The dose reductions are substantial. In one analysis of patients receiving whole-breast or post-mastectomy radiation with DIBH, the mean heart dose was cut by more than half, and dose to the left anterior descending coronary artery dropped by roughly 40% compared to free-breathing treatment.15PubMed Central. Deep-inspirational breath-hold (DIBH) technique in left-sided breast cancer: various aspects of clinical utility Another study found mean dose reductions to the heart, left anterior descending artery, left ventricle, and right ventricle of 30%, 39%, 39%, and 35% respectively.16PubMed Central. Cardiac exposure in left-sided breast cancer patients undergoing deep inspiratory breath hold radiation therapy Since radiation-related heart disease is a long-term concern for breast cancer survivors, this simple act of holding a breath during treatment can meaningfully improve outcomes years down the road.
What Happens Inside Your Brain During a Breath Hold
Your brain is the organ most sensitive to oxygen deprivation, so it makes sense that it receives special treatment during apnea. As carbon dioxide rises and oxygen falls, blood vessels in the brain dilate to increase blood flow, compensating for the reduced oxygen content. Trained freedivers show this effect at a remarkable scale. In one study, freedivers increased cerebral blood flow by 107% during breath holds, enough to maintain oxygen delivery to the brain even as their arterial oxygen saturation dropped.17PubMed Central. Cerebral metabolism and vascular reactivity during breath-hold and hypoxic challenge in freedivers and healthy controls
This protective mechanism has limits, though. Even in experienced divers, cerebral oxygen saturation can drop by about 13% by the end of a maximal breath hold, despite the surge in blood flow.18PubMed. Cerebral and peripheral hemodynamics and oxygenation during maximal dry breath-holds And when researchers pharmacologically blocked the brain’s ability to vasodilate (using indomethacin), cerebral blood flow at the end of apnea was roughly 27% lower than normal, demonstrating how dependent the brain is on this compensatory vasodilation to survive the breath hold.19PubMed Central. Role of cerebral blood flow in extreme breath holding
There is also evidence that apnea temporarily affects the blood-brain barrier. Trained divers show transient increases in a protein called S100B after breath holds, rising from about 0.066 to 0.083 micrograms per liter. Researchers attribute this to brief, non-pathological opening of the blood-brain barrier caused by the combined stress of asphyxia and blood pressure changes.20PubMed. Increased serum levels of the brain damage marker S100B after apnea in trained breath-hold divers: a study including respiratory and cardiovascular observations A separate study in competitive divers also found elevated S100β alongside increased oxidative stress markers but interpreted the blood-brain barrier disruption as minor rather than damaging.21PubMed. Competitive apnea and its effect on the human brain: focus on the redox regulation of blood-brain barrier permeability and neuronal-parenchymal integrity
When Breath Holding Becomes Dangerous
For casual, short breath holds, the breaking point reflex is an effective safety net. Your body forces you to breathe long before you are in any real danger. The risks escalate when people learn to override or delay that reflex, which is exactly what competitive and commercial breath-hold divers do.
An MRI study of Japanese Ama divers, who commercially dive for shellfish using only breath holds, found that 11 out of 12 divers had ischemic brain lesions, located in areas including the cortical and subcortical regions, white matter, and basal ganglia. Four of the 12 had histories of cerebral decompression illness events.22PubMed Central. Brain damage in commercial breath-hold divers These were older, career divers with decades of cumulative exposure, so the findings do not apply to someone doing occasional breath-hold exercises. But they are a sobering reminder that the brain’s protective mechanisms can be overwhelmed by years of extreme apnea.
Cognitive testing tells a similar story. When elite breath-hold divers were compared to other athletes and non-athletes, the divers performed worse on a test of cognitive interference, taking longer and making more errors. The degree of impairment correlated with both the duration of their longest static breath hold and the number of years they had been training.23PubMed. Do elite breath-hold divers suffer from mild short-term memory impairments? The researchers characterized these as mild but persistent impairments. This is the evidence that gets lost when breath holding is presented as a purely beneficial practice: at the extreme end, cumulative hypoxic exposure appears to carry a neurological cost.
Cold Water, Breath Holding, and Cardiac Risk
One specific scenario deserves its own warning. Holding your breath while immersing yourself in cold water creates what researchers call “autonomic conflict.” The diving response triggered by apnea slows the heart via the parasympathetic nervous system, while the cold shock response simultaneously activates the sympathetic nervous system to speed it up. These two opposing signals hitting the heart at the same time produce cardiac arrhythmias at an alarming rate. In experiments with young, fit, healthy volunteers, simultaneous cold-water immersion and breath holding produced arrhythmias in 62% to 82% of participants.24PubMed Central. ‘Autonomic conflict’: a different way to die during cold water immersion?
This is particularly relevant for anyone practicing cold-water swimming, ice baths combined with breath work, or entering cold water unexpectedly. The arrhythmias in these studies occurred in people who had no heart conditions. The combination of breath holding and cold immersion is physiologically distinct from either one alone, and it is one of the proposed mechanisms for unexplained drowning deaths in otherwise healthy individuals.
Lung Adaptations in Long-Term Divers
Long-term breath-hold divers tend to develop measurably larger lungs. A study of breath-hold diving fishermen found that their forced vital capacity and forced expiratory volume were significantly higher than both the control group and their own predicted values, with no signs of airway obstruction.25PubMed. Chronic adaptations of lung function in breath-hold diving fishermen Competitive breath-hold divers showed a similar pattern: higher than predicted ventilatory flows and volumes, with no impairment of gas transfer or inspiratory muscle strength compared to controls.26PubMed. Characteristics of the respiratory mechanical and muscle function of competitive breath-hold divers
It remains unclear how much of this is training adaptation versus self-selection. People born with naturally larger lungs may be drawn to and succeed in breath-hold diving, creating an artificial correlation. But the fishermen study is interesting because these were working divers, not self-selected competitive athletes. Either way, casual breath-hold practice is unlikely to meaningfully change your lung volumes. These are adaptations observed after years of intensive, daily diving.
Cardiovascular Health in Elite Divers
A reasonable concern is whether repeated bouts of oxygen deprivation would eventually damage the cardiovascular system, the way obstructive sleep apnea does. Sleep apnea is strongly associated with high blood pressure and sustained sympathetic nervous system activation. But at least one study of elite breath-hold divers found no evidence of this pattern. Their resting sympathetic activity and blood pressure were normal, leading researchers to conclude that repeated voluntary hypoxemia does not drive the same sustained sympathetic activation seen in sleep apnea, possibly because it lacks the additional factors like sleep fragmentation and obesity that make sleep apnea harmful.27PubMed. Central chemoreflex sensitivity and sympathetic neural outflow in elite breath-hold divers
Separately, a study of elite freedivers found that apnea-induced oxidative stress was accompanied by increases in heat shock proteins and nitric oxide-related signaling that appeared to be cardiovascularly protective rather than damaging.28Frontiers in Physiology. Effect of Apnea-Induced Hypoxia on Cardiovascular Adaptation and Circulating Biomarkers of Oxidative Stress in Elite Breath-Hold Divers These findings suggest that the cardiovascular system adapts favorably to controlled, voluntary breath holding, at least in trained individuals. Whether the same applies to beginners doing aggressive breath-hold protocols at home is a different question.
Breath-Hold Exercises and Stress Reduction
Many people are drawn to breath holding not for athletic gains but for its calming effects. Slow breathing and brief breath retentions are staples of yoga, meditation, and clinical relaxation protocols. The physiological basis is that slowing the breath and pausing shifts autonomic balance toward the parasympathetic side, the “rest and digest” branch of the nervous system.
The evidence here is real but nuanced. A study of people with high generalized anxiety scores found that a resonance frequency breathing exercise (slow, paced breathing near the body’s natural cardiovascular rhythm) increased heart rate variability during the session, a marker associated with parasympathetic tone. However, the effect did not carry over into improved cognitive performance or reduced worry in that single-session experiment.29PubMed Central. Effects of A Brief Resonance Frequency Breathing Exercise on Heart Rate Variability and Inhibitory Control in the Context of Generalised Anxiety Disorder And a randomized controlled trial comparing daily breathwork with mindfulness meditation found that neither group showed significant changes in resting heart rate variability over the study period, even though mood improved in the breathwork group.30Cell Reports Medicine. Brief daily meditation and breathing practices differentially affect mood and physiology: A randomized controlled trial So while breathing exercises that include brief holds can improve how you feel in the moment, the idea that they permanently reset your nervous system’s baseline is not yet well supported.
Genetic Echoes of Breath-Hold Diving
Perhaps the most striking evidence that breath holding carries biological significance comes from the Bajau people of Southeast Asia, sometimes called “Sea Nomads.” They have practiced subsistence freediving for thousands of years, spending hours each day underwater collecting fish and shellfish. Researchers found that the Bajau have genetically larger spleens than neighboring non-diving populations, and they traced this to natural selection on a gene called PDE10A.31PubMed. Physiological and Genetic Adaptations to Diving in Sea Nomads A larger spleen provides a bigger reservoir of red blood cells to release during dives, extending the oxygen supply available during each apnea.
The finding is a vivid illustration of how the spleen-contraction response described earlier is not just a physiological curiosity but an adaptation important enough for evolution to amplify. Even Bajau individuals who do not personally dive carry the enlarged-spleen variants, confirming that the trait is genetic rather than a training effect.32Cell. Physiological and Genetic Adaptations to Diving in Sea Nomads For the rest of us without a few thousand years of selective pressure, the spleen contraction still happens during apnea, just at a more modest scale.
Breath-Holding Spells in Toddlers
If you are a parent who has watched a toddler cry so hard they turned blue and briefly lost consciousness, you may have wondered whether that counts as a dangerous breath hold. These episodes, called breath-holding spells, are considered a benign condition occurring in otherwise healthy children between about 6 and 48 months of age. They are triggered by emotional upset or minor injury, and progress through crying, breath holding, color change, and sometimes a brief faint.33PubMed Central. Breath-holding spells in infants Despite how terrifying they look, they are not a form of seizure, do not indicate a neurological problem, and children outgrow them. They are worth mentioning here mainly to reassure any parent who arrived at this topic through that particular search.