The Relaxation Response and Stress Physiology: What Is Known

What the stress response is

MedlinePlus describes stress as how your brain and body respond to a challenge or demand. When you are stressed, your body releases hormones that make you alert and ready to act, and that can raise blood pressure, heart rate and blood sugar. This is sometimes called the "fight or flight" response. [1] A little short-term stress can be helpful, but MedlinePlus says stress that lasts a long time can harm health. [1]

On the nervous system side, NHLBI explains that the sympathetic system increases heart rate, blood pressure, breathing rate and pupil size, while the parasympathetic system slows the heart and relaxes muscles in the digestive tract. [2]

The relaxation response

NCCIH defines relaxation techniques as practices that help bring about the body's "relaxation response," characterized by slower breathing, lower blood pressure and a reduced heart rate, and says the relaxation response is the opposite of the stress response. [3] The techniques it lists are breathing exercises, progressive relaxation, autogenic training, guided imagery, biofeedback-assisted relaxation and self-hypnosis. [3]

The term is associated with the physician Herbert Benson. PubMed lists a 1974 paper titled "The relaxation response" by Benson, Beary and Carol in the journal Psychiatry. [4] We could read only the record and not the abstract, so we do not describe the original findings here. A 2013 laboratory study of the response measured gene activity in blood before and after a session of relaxation-response practice; its authors describe the relaxation response as the counterpart of the stress response and report changes in gene expression linked to energy metabolism and inflammation, but the study measured a molecular signal rather than health outcomes. [5]

What breathing adds

Slow breathing is one route to the response. A 2018 systematic review of 15 studies in healthy people found that slow breathing (fewer than 10 breaths a minute) was linked with higher heart rate variability and with reports of more comfort and relaxation and less anxiety, anger and low mood. [6] A larger 2022 review of 223 studies found vagally-mediated heart rate variability increased during and after voluntary slow breathing. [7] For the gentle version, see gentle breathing and relaxation practices.

Evidence by outcome

Where the story is oversimplified

• A heart-rate-variability change is not the same as "vagal tone". A review of respiratory sinus arrhythmia (the rise and fall of heart rate with breathing) listed several caveats about treating it as a direct measure of the vagus nerve's activity. [10] A methods paper adds that heart rate variability findings can be easily misconstrued. [11]
• Mechanisms are still debated. A 2025 review said recent findings have challenged several foundational concepts traditionally believed to underlie the effects of breathwork. [12]
• A lab response is not a cure. A drop in a measure during a session does not show lasting benefit. The 2018 review noted that its explanations are hypotheses. [6]
• Not everyone relaxes. NCCIH reports occasional increased anxiety, intrusive thoughts or fear of losing control with relaxation techniques. [3]

More on the nervous system is on the autonomic nervous system and breathing, and on breathing and vagus nerve claims.