What Is the Vagus Nerve? A Science-Backed Guide to Vagal Tone, Stress, and Cold Plunging
Take a slow breath in, then let it out for twice as long. If your shoulders dropped a little, you just used your vagus nerve.
The vagus nerve is the longest cranial nerve in your body, and it is the main line of communication between your brain and your heart, lungs, and gut. It helps set your heart rate, runs your digestion, and acts as the brake pedal on your stress response. It is also one of the most searched, and most misunderstood, topics in health right now.
This guide explains what the vagus nerve is, what it does, how scientists measure its activity, and which methods of stimulating it hold up to scrutiny. We finish with the question we get asked most: what does a cold plunge do to your vagus nerve?
The short version
- The vagus nerve is cranial nerve X. It runs from your brainstem to your abdomen and is the main nerve of the parasympathetic ("rest and digest") nervous system.
- Most of its fibers are sensory. It spends more time reporting on your body to your brain than giving orders.
- "Vagal tone" describes how strongly the vagus slows your heart at rest. It is estimated with heart rate variability (HRV).
- Slow exhales, exercise, humming, and cold water on the face all act on vagal pathways, with different levels of evidence.
- A cold plunge first triggers a stress response, then a vagal rebound. Getting your face wet and controlling your exhale are what tip the balance toward the vagus.
What Is the Vagus Nerve?
The vagus nerve is the tenth of your twelve cranial nerves, which is why you will see it written as cranial nerve X or CN X. Its name comes from the Latin word for "wandering," and it earns it. No other cranial nerve travels as far.
You actually have two vagus nerves, a left and a right. Each one starts in the medulla oblongata at the base of your brainstem, exits the skull, and runs down the neck alongside the carotid artery. From there it branches to the throat and voice box, the heart, the lungs, and the esophagus, then continues into the abdomen to reach the stomach, pancreas, spleen, kidneys, and small intestine (StatPearls).
A two-way street that mostly runs one direction
The vagus is a mixed nerve. It carries motor signals from the brain down to your organs and sensory signals from your organs back up to the brain.
Most people picture it as a command cable. It is closer to a surveillance network. Stanford neuroscientist Andrew Huberman puts the split at about 85% sensory fibers and 15% motor fibers (Huberman Lab). Your vagus nerve is constantly telling your brain how stretched your gut is, how full your lungs are, and what the chemistry of your digestive tract looks like. Your brain uses that feed to decide how alert, calm, hungry, or uneasy you should feel.
That is the real reason a "gut feeling" is more than a figure of speech.
What Does the Vagus Nerve Do?
Your autonomic nervous system has two main branches. The sympathetic branch is the accelerator: it raises heart rate and mobilizes energy for "fight or flight." The parasympathetic branch is the brake: it slows things down for "rest and digest." The vagus nerve is the main nerve of the parasympathetic branch.
Here is what it handles day to day.
| System | What the vagus nerve does |
|---|---|
| Heart | Sends signals to the heart's natural pacemaker that slow your heart rate, beat by beat |
| Lungs | Senses how far your lungs are inflated and helps tie breathing to heart rate |
| Digestion | Drives the muscle contractions and gland secretions that move and break down food |
| Throat and voice | Controls most of the muscles used for swallowing and speaking |
| Gut-brain signaling | Reports gut stretch and gut chemistry, including serotonin levels, up to the brain |
| Immune system | Carries the "inflammatory reflex," a nerve circuit that helps keep inflammation in check |
Two of these deserve a closer look.
The inflammatory reflex. In 2002, neurosurgeon Kevin Tracey described in Nature how the nervous system regulates inflammation reflexively, in real time, much as it regulates heart rate (Tracey, 2002). The vagus nerve is the wiring for that reflex. This is the science behind the claim that the vagus nerve "reduces inflammation," and it is why researchers are testing vagus nerve stimulation for inflammatory conditions.
The gut-brain axis. Much of your body's serotonin is made in the gut. Gut serotonin does not travel to the brain directly. The vagus nerve senses it and relays that information upward, where it influences mood (Huberman Lab).
The vagus nerve matters enough that doctors stimulate it directly. Implanted vagus nerve stimulators are approved to treat epilepsy and depression (StatPearls).
It is not only a "calm down" nerve
This is the part most articles miss. In his 2025 episode on the vagus nerve, Huberman explains that the vagus can also wake you up. When you move the large muscles of your legs and trunk, your adrenal glands release adrenaline. Adrenaline cannot cross into the brain, so it acts on the vagus nerve, which relays the signal to the brainstem and on to the locus coeruleus. That structure releases norepinephrine, and you feel alert and motivated.
So the vagus nerve is better understood as a regulator than a sedative. It reads the state of your body and helps your brain match it. Keep that in mind when we get to cold water.
What Is Vagal Tone, and How Is It Measured?
"Vagal tone" describes how active your vagus nerve is at rest, and in particular how strongly it holds your heart rate down. You cannot measure it directly without wiring up the nerve. Researchers estimate it with heart rate variability, or HRV.
HRV is the variation in time between one heartbeat and the next. A healthy heart does not tick like a metronome. It speeds up slightly each time you inhale and slows each time you exhale, because the vagus nerve applies the brake on the exhale. The more responsive that brake, the more your beat-to-beat timing varies.
Three things are worth knowing about HRV:
- Higher is generally better. Higher HRV is associated with better health outcomes, and HRV tends to decline with age (Huberman Lab).
- Your wearable is already tracking it. Most smartwatches, rings, and chest straps report HRV, often as a number called RMSSD. That is the same measure researchers use to estimate vagal activity.
- Compare yourself to yourself. HRV varies widely between people. Your own trend over weeks tells you more than any single reading or anyone else's number.
HRV is useful because it turns a vague idea into something you can track. If a practice claims to "stimulate the vagus nerve," the fair question is whether it moves heart rate or HRV in a controlled study.
How to Stimulate the Vagus Nerve Naturally
Search "vagus nerve exercises" and you will find everything from gargling to eye rolls. Some methods have controlled studies behind them. Others have a plausible mechanism and not much else. Here is how the common ones stack up.
| Method | How it works | What the evidence shows |
|---|---|---|
| Long, slow exhales | Exhaling engages the vagal brake on the heart | Strong. In a Stanford trial of 111 adults, five minutes a day of exhale-focused "cyclic sighing" improved mood more than mindfulness meditation and lowered resting breathing rate (Stanford Medicine) |
| Cold on the face or neck | Cold receptors in the face and neck trigger a reflex that slows the heart | Good for short-term effects. Covered in detail below |
| Exercise | Adrenaline released by working muscles signals the brain through the vagus | Well-described pathway for alertness. Regular activity also helps slow the age-related decline in HRV |
| Humming | Vibration mechanically activates the vagal branches that serve the voice box | Plausible mechanism. Described by Huberman as a reliable calming tool, slower than breathing |
| Fermented foods | Supports the gut microbes involved in serotonin production, which the vagus reports to the brain | Indirect. Supports the signal the vagus carries more than the nerve itself |
| Ear massage | A small sensory branch of the vagus serves the outer ear | Mild. Huberman notes it will not produce a large shift, especially under real stress |
If you only try one, make it the exhale. It is free, it works in seconds, and it has the best data. We will come back to it, because it is also the single most useful skill to bring into a cold plunge.
A note on expectations: these practices nudge a healthy nervous system toward calm. They do not treat medical conditions. If you have symptoms like fainting, a persistently racing heart, or ongoing digestive problems, see a doctor.
What Andrew Huberman Says About the Vagus Nerve
Dr. Andrew Huberman is a neuroscientist at Stanford and host of the Huberman Lab podcast. In June 2025 he released a full solo episode on the topic, "Control Your Vagus Nerve to Improve Mood, Alertness & Neuroplasticity." These are the tools from that episode that are most worth using.
- The physiological sigh. Two inhales through the nose, then one long exhale through the mouth. Huberman calls it the fastest way to calm down in real time. His own lab co-led the Stanford trial on a five-minute version of this practice.
- Deliberate exhales through the day. For long-term improvement, he suggests slowing your heart rate with an extended exhale roughly 10 to 20 times a day. His reasoning is that repetition strengthens the pathway from the prefrontal cortex to the vagus, which raises HRV over time, including during sleep.
- Exercise for alertness. A warm-up followed by short, higher-intensity efforts uses the adrenaline-to-vagus pathway described above to raise focus. He recommends scheduling learning in the hours after a workout that leaves you energized.
- Humming. Lengthen the "h" sound, not the "m," so the vibration sits in the throat where vagal branches serve the larynx.
- A neck stretch. Seated with elbows planted on a table, press the elbows down and look up and to one side, then the other. He describes it as slower and less robust than the physiological sigh.
- Feed the gut. One to four servings a day of low-sugar fermented foods such as kimchi, sauerkraut, kefir, or plain yogurt, to support gut serotonin.
What Huberman says about cold water
Huberman's vagus nerve episode does not focus on cold exposure. His cold guidance comes from his cold exposure newsletter and other appearances. The points most relevant here:
- Dose: aim for a total of 11 minutes per week, split across two to four sessions of one to five minutes each.
- Temperature: cold enough that you think, "This is really cold, and I want to get out, but I can safely stay in." He notes that could be 60°F for some people and 45°F for others.
- Brain chemistry: cold triggers a significant release of epinephrine and norepinephrine and a prolonged rise in dopamine, which is why mood and focus stay elevated afterward.
- Face first: on The Joe Rogan Experience, Huberman explained why experienced plungers dunk their face as they get in. "When you put your face in the water right as you go in, you activate the mammalian dive reflex," he said. "It lowers your heart rate, it makes you calmer, and it makes you better able to tolerate stress" (as reported here).
That last point is the bridge between the vagus nerve and your cold plunge.
How Cold Plunging Impacts the Vagus Nerve
Most cold plunge articles say cold water "activates the vagus nerve" and leave it there. The real story is more interesting, because a cold plunge pulls on both branches of your nervous system at once. What happens comes in three phases.
Phase 1: The cold shock (first 30 seconds)
When cold water hits your skin, the first response is not vagal at all. It is sympathetic. You gasp, your breathing speeds up, and your heart rate jumps. Physiologists call this the cold shock response.
A study of 26 divers in near-freezing water captured this clearly. On immersion with their faces still out of the water, parasympathetic activity dropped and sympathetic activity rose sharply (Lundell et al., 2021).
Phase 2: The dive reflex (face in the water)
Then the same study found something useful. Once the divers put their faces in the water, parasympathetic activity rose again.
This is the mammalian dive reflex. Cold receptors on your face send a signal through the trigeminal nerve to the brainstem, and the brainstem answers through the vagus nerve by slowing the heart. Other research points the same way:
- Face immersion raises HRV. In a study of 15 men, immersing the face increased heart rate variability across a range of breathing rates. The authors concluded that face immersion alone increases vagal activity (Hayashi et al., 1997).
- Cold on the neck slows the heart. In a randomized controlled trial with 61 participants analyzed, cold applied to the side of the neck raised HRV and lowered heart rate. Cold on the cheek also raised HRV. Cold on the forearm did not (Jungmann et al., 2018).
The pattern is consistent: where the cold lands matters. The face and neck are the body's vagal triggers. A plunge that covers you to the neck, with a face dunk on entry, hits both.
Phase 3: The settle (and the long game)
After the first half minute, the stress response starts to fade and you have a choice. Panic-breathe and stay in fight or flight, or lengthen your exhale and let the vagal brake take over. This is the moment that makes cold plunging a training tool. You are practicing calm while your body is under real, measurable stress.
That practice appears to carry over. In a study of experienced winter swimmers, the swimmers showed a smaller rise in pulse and blood pressure in response to cold than non-swimmers did (University of Copenhagen). Their bodies took the hit without overreacting.
What the science does not show yet
We would rather be accurate than hyped. The studies above are small, most measure short-term effects, and several used cold on the face or neck instead of a full plunge. The winter swimmer study had 16 men and cannot prove the swimming caused the difference. No study has yet proven that regular cold plunging permanently raises resting vagal tone.
What the evidence supports is this: cold on the face and neck reliably triggers a vagal response in the moment, and regular cold exposure is associated with a calmer reaction to cold stress over time. That is a strong enough case to make the plunge a smart place to train your nervous system, and it matches what most plungers report feeling afterward: alert, clear, and calm at the same time.
A Vagus-Friendly Cold Plunge Routine
Here is how to put the science to work. This routine is built around the two levers that favor the vagus nerve: cold on the face and neck, and a long exhale.
- Set a temperature you can repeat. Start at 55 to 60°F and work down over weeks. Use Huberman's test: it should feel very cold, and you should want to get out, but you can safely stay in.
- Breathe before you get in. Take three physiological sighs: two inhales through the nose, one long exhale through the mouth. Never hyperventilate before or during a plunge.
- Get in steadily, to the neck. Lower yourself in over a few seconds instead of inching in. Submerge your shoulders and the sides of your neck.
- Dunk or splash your face. A brief face dip as you enter triggers the dive reflex. If you prefer to keep your head dry, splash cold water on your face and cheeks.
- Exhale through the first 30 seconds. This is the cold shock window. Breathe in through the nose and make every exhale about twice as long as the inhale. Your heart rate will follow your breath down.
- Stay one to five minutes. Build toward a weekly total of about 11 minutes across two to four sessions. Colder water needs less time.
- Warm up naturally. Get out, dry off, and move around. Let your body reheat on its own when you can.
A plunge with a chiller makes step one much easier, because the water is the same temperature every session. Consistent temperature is what lets you track progress, both on the clock and in your HRV data. Shop Icebound all-in-one cold plunge tub and chiller systems →
Not sure which setup fits your space and budget? Read our cold plunge buying guide.
Safety first
Cold water is a real stressor, and the vagus nerve is part of the reason to respect it. The cold shock response speeds the heart up while the dive reflex slows it down. Researchers call this "autonomic conflict," and they have proposed it as a cause of abnormal heart rhythms in cold water, even in healthy volunteers (Shattock and Tipton, 2012).
For most healthy people a controlled plunge is well tolerated, but take these precautions:
- Talk to your doctor first if you have a heart condition, high blood pressure, a history of fainting, or are pregnant.
- Keep face dips to a few seconds. Do not do long breath holds underwater or combine plunging with hyperventilation-style breathwork.
- Do not plunge alone when you are new to it, and never in open water you cannot exit easily.
- Start warmer and shorter than you think you need. Adaptation takes weeks.
- Skip the plunge right after strength training if muscle growth is your goal. Huberman suggests waiting six to eight hours, or plunging before you train. We cover timing in detail in Ice Bath: Before or After Your Workout?
The Bottom Line
The vagus nerve is your body's main line between brain and organs, and its job is regulation: slowing the heart, running digestion, reporting on the gut, and keeping inflammation in check. You can measure its influence through HRV and train it with tools as simple as a long exhale.
A cold plunge is one of the few places you can practice that skill under pressure. The cold supplies the stress. Your face, your neck, and your breath supply the brake. Do it consistently and you are teaching your nervous system to stay steady when things get uncomfortable, in the water and out of it.
Explore Icebound all-in-one cold plunge systems →
Vagus Nerve FAQ
Where is the vagus nerve located?
You have a left and a right vagus nerve. Each starts in the brainstem, runs down the side of the neck next to the carotid artery, and branches to the throat, heart, lungs, and digestive organs.
What does the vagus nerve do?
It is the main nerve of the parasympathetic nervous system. It slows heart rate, drives digestion, controls muscles for swallowing and speech, carries sensory information from the organs to the brain, and helps regulate inflammation.
What is vagal tone?
Vagal tone is the level of vagus nerve activity at rest, especially its slowing effect on the heart. It is estimated with heart rate variability (HRV). Higher HRV generally reflects higher vagal tone.
How can I stimulate my vagus nerve at home?
The best-supported method is slow breathing with long exhales, such as the physiological sigh. Cold water on the face or neck, regular exercise, and humming also act on vagal pathways.
Does a cold plunge stimulate the vagus nerve?
Yes, with a caveat. The first seconds of a plunge trigger a stress response. Cold on the face and neck then triggers the dive reflex, which slows the heart through the vagus nerve. Wetting your face and extending your exhale strengthen that response.
Does a cold shower work for the vagus nerve?
A cold shower that runs over the face and neck can trigger the same reflex. A plunge gives more consistent temperature and coverage, which makes the effect easier to repeat and track.
How long should I cold plunge for vagus nerve benefits?
One to five minutes per session is enough. Andrew Huberman's general guideline is about 11 minutes per week in total, spread across two to four sessions.
What does Andrew Huberman say about the vagus nerve?
Huberman describes the vagus as a two-way pathway that is about 85% sensory. He says it can calm you or raise alertness depending on which pathway is active. His top tools are the physiological sigh, deliberate long exhales 10 to 20 times a day, exercise, humming, and fermented foods for gut health.
Is cold plunging safe for everyone?
No. Cold water places sudden demands on the heart. People with heart conditions, high blood pressure, or a history of fainting, and anyone who is pregnant, should talk to a doctor first.
References
- Kenny BJ, Bordoni B. Neuroanatomy, Cranial Nerve 10 (Vagus Nerve). StatPearls. Updated November 2022.
- Huberman A. Control Your Vagus Nerve to Improve Mood, Alertness & Neuroplasticity. Huberman Lab podcast. June 23, 2025.
- Huberman A. The Science and Use of Cold Exposure for Health and Performance. Huberman Lab newsletter.
- Tracey KJ. The inflammatory reflex. Nature. 2002;420(6917):853-859.
- Stanford Medicine. "Cyclic sighing" can help breathe away anxiety. February 2023. Reports on Balban MY et al., Cell Reports Medicine, 2023.
- Hayashi N, Ishihara M, Tanaka A, Osumi T, Yoshida T. Face immersion increases vagal activity as assessed by heart rate variability. Eur J Appl Physiol Occup Physiol. 1997;76(5):394-399.
- Jungmann M, Vencatachellum S, Van Ryckeghem D, Vögele C. Effects of Cold Stimulation on Cardiac-Vagal Activation in Healthy Participants: Randomized Controlled Trial. JMIR Formative Research. 2018;2(2):e10257.
- Lundell RV, Tuominen L, Ojanen T, Parkkola K, Räisänen-Sokolowski A. Diving Responses in Experienced Rebreather Divers: Short-Term Heart Rate Variability in Cold Water Diving. Frontiers in Physiology. 2021;12:649319.
- University of Copenhagen. Winter-swimming Scandinavian men can teach us how the body adapts to extreme heat and cold. October 2021. Reports on Søberg S et al., Cell Reports Medicine, 2021.
- Shattock MJ, Tipton MJ. "Autonomic conflict": a different way to die during cold water immersion? The Journal of Physiology. 2012;590(14):3219-3230.
- Calfkicker. Andrew Huberman explains to Joe Rogan why experienced cold plungers dunk their face first in the water. Secondhand report of a Joe Rogan Experience episode.
This article is for educational purposes and is not medical advice.
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