An instruction that sounds like superstition
The first time a teacher tells you to close your right nostril with your thumb and breathe only through the left, it sounds like folklore. Why would the side of the nose matter? Air is air. You have two nostrils feeding one throat, one pair of lungs, one bloodstream. Blocking one channel to calm yourself down has the flavor of a charm rather than a physiology.
But the instruction is older and more careful than it looks. In the Haṭha Yoga tradition it has a name — Chandra Bhedana, roughly "piercing the moon" — and it belongs to a family of practices built on a genuine, measurable asymmetry in how your nose works. Most of us have simply never noticed it.
Your nose is already taking turns
Here is the part that surprises people: at almost any given moment, you are not breathing equally through both nostrils. One is more open, the other more congested, and every few hours they quietly swap.
This is the nasal cycle, and it is well documented in otolaryngology. The turbinates — curled shelves of tissue lining each nasal passage — are wrapped in erectile tissue much like the tissue that swells elsewhere in the body. Your autonomic nervous system controls how engorged that tissue is, alternately narrowing one side while opening the other. You don't feel it because your total airflow stays roughly constant; the two sides simply trade the load. Cover one nostril and breathe, then the other, and you can usually feel which one is currently "open."
That cycle is the substrate the yogis were working with. They didn't have the anatomy, but they had the observation: the nose has a rhythm, and that rhythm is tied to how alert or settled you feel.
The two channels the tradition named
Haṭha Yoga maps two energetic channels alongside the spine. Ida, associated with the left nostril, is called lunar — chandra, the moon — and described as cooling, quieting, inward. Pingala, associated with the right, is solar — surya, the sun — heating, activating, outward. The whole architecture of nostril-based pranayama comes from this pairing: if you want to warm and wake the body, you emphasize the right, the sun channel; if you want to cool and calm it, you emphasize the left, the moon.
Chandra Bhedana is the moon practice. You deliberately draw the breath in through the left nostril, favoring the lunar channel, to steer yourself toward stillness. Its solar twin, Surya Bhedana, does the opposite through the right.
You can treat Ida and Pingala as metaphor and still take the practice seriously, because the metaphor turns out to sit on top of something the lab can see.
What the lateralization research actually shows
Starting in the late 1980s, the researcher David Shannahoff-Khalsa and colleagues studied what they called forced unilateral nostril breathing — deliberately breathing through only one side. Across several small studies, right-nostril breathing tended to shift markers toward sympathetic arousal, the body's activating branch, while left-nostril breathing was associated with a relatively more parasympathetic, settling profile. Other work has reported that left-nostril breathing can nudge blood pressure and heart rate downward compared with right-nostril breathing.
It is worth being honest about the state of this evidence. The studies are generally small, the effects are modest, and the literature is mixed rather than settled. The leading explanations are still hypotheses: that the dense trigeminal nerve endings in each nasal passage feed slightly asymmetric signals upward, and that the brain's own left–right differences in autonomic control get gently engaged by which side you breathe through. No one is claiming that closing a nostril flips a switch in your nervous system.
So the accurate way to hold it is this: left nostril breathing is a small, real lateralized nudge toward the calming side of the autonomic nervous system — not a magic lever, but not nothing either.
How to actually do it
Sit upright, somewhere you won't be interrupted. Rest your left hand in your lap. With your right hand, you'll use the breath to close and open the nostrils — many practitioners fold the index and middle fingers down and use the thumb for the right nostril and the ring finger for the left (this hand shape is called Vishnu mudra), but any gentle, comfortable pinch works.
Close your right nostril with your thumb. Breathe in slowly and smoothly through the left nostril alone, drawing the breath low into the belly rather than high into the chest. Let it be unhurried — there is no target speed, only the absence of strain.
From here there are two common versions. The simplest is to keep the right nostril closed and breathe both in and out through the left for the whole practice. The more classical Chandra Bhedana asks you to inhale through the left, then close the left and exhale through the right, keeping the cooling inhale on the moon side. Either is fine when you're learning; start with whichever you can do without tensing your hand or holding your breath awkwardly.
Do it for a few minutes — a dozen or two slow rounds. Evening is the natural home for it: the hour when you're overheated from the day, wired but tired, or lying awake with a mind that won't power down. It's a poor choice first thing on a morning you need to get moving; that's what the sun channel is for.
One caution: this is a subtle, cooling practice, not a strenuous one. If you feel lightheaded, simply return to normal breathing through both nostrils.
Where it helps, and where it doesn't
It would be easy to oversell this, so let's not. The heavy lifting in any calming breath practice is done by two things the research is much more confident about: breathing slowly, and letting your exhale be longer and softer than your inhale. Those alone reliably tip you toward the parasympathetic "rest" state. Chandra Bhedana works best layered on top of them — a slow, long-exhale breath that also happens to favor the left nostril. The nostril choice is the fine-tuning, not the engine.
What the practice really gives you is a form of attention. Choosing a nostril forces you to notice your breath as a physical event with a texture and a direction, and that noticing is itself steadying. You stop being a person who is anxious and become, for a few minutes, a person studying the cool thread of air moving along the left side of the nose. The tradition and the lab meet somewhere in that shift.
Bringing it into a practice that lasts
The hard part was never the technique — it's remembering to reach for the right one at the right moment, and doing it often enough that it becomes a reflex rather than an emergency measure. That's the gap Prāṇa is built to close. It delivers a personalized daily breathing practice rooted in the Haṭha Yoga tradition, so a cooling moon-channel breath like Chandra Bhedana shows up when the evening calls for it and the solar practices show up when the morning does — guided, paced, and shaped to where you actually are rather than to a generic script.
If you'd like the tradition's breath work to become a quiet daily habit instead of a thing you read about once, you can find it at prana.lumenlabs.works. Tonight, though, you don't need anything but your thumb and a few slow breaths through the left.