Box breathing calms the mind, but your heart may not notice

Box breathing, also called square breathing, cycles through equal phases of inhaling, holding, exhaling and holding again. It is widely promoted as a simple technique for stress reduction and for regulating the nervous system, and it costs nothing and takes minutes to learn. Popularity is not proof, though, and the randomised trial evidence for box breathing specifically, rather than slow breathing in general, has been limited and fragmented. This review set out to gather every trial that tested the equal phase pattern as the main intervention and ask what it actually delivers.

The authors searched PubMed, Scopus, Web of Science and ClinicalTrials.gov for randomised controlled trials published up to 2025. Trials qualified only if box breathing, the equal phase inhale, hold, exhale, hold pattern, was the primary intervention rather than one element of a broader programme. Study quality was assessed with a standard risk of bias tool. Because the trials differed so much in populations, protocols and outcome measures, the findings were described narratively rather than pooled into a single number. Eight eligible trials emerged, covering healthy adults as well as postpartum women and women recovering from surgery.

Several trials reported short-term benefits on perceived stress, perceived anxiety and mood, though not uniformly across studies. Physiological responses were mixed: some trials saw a slower breathing rate, others recorded changes in heart rate or heart rate variability. More recent evidence suggests box breathing can blunt certain acute stress responses, including heart rate, state anxiety and salivary alpha-amylase, but not heart rate variability or cortisol. On the clinical side, trials reported reduced postpartum pain and improvement in some lactation-related outcomes. No trial measured lung function with spirometry or maximal aerobic capacity.

This appears to be the first dedicated synthesis of trials testing box breathing on its own terms rather than folding it into breathing techniques generally. The picture is consistent with the wider breathwork literature: subjective calm arrives more reliably than measurable shifts in the body's stress systems. It complicates the framing of box breathing as an autonomic regulation tool, since the autonomic findings were inconsistent and cortisol did not move. Open questions remain about the best protocol, how long any effect lasts, and whether standardised breathing prescriptions would produce more consistent physiology.

If you use box breathing to settle yourself before a stressful moment, this review offers modest support: short-term reductions in perceived stress and anxiety showed up in several trials. It is less encouraging for anyone expecting deeper physiological change, since heart rate variability and cortisol were largely unmoved. With only eight trials, varied methods and little long-term follow-up, the honest reading is that box breathing is a low-cost tool for in-the-moment calm whose bigger claims remain unproven. Nothing here suggests harm, and nothing here suggests it replaces anything else you do for stress.