Side sleeping is the best position for most people. It supports spinal alignment, keeps airways open, aids digestion, and may even help the brain clear waste more efficiently during the night. More than 60% of adults already sleep on their side, making it the most common position by a wide margin. But “best” depends on your body and your specific health concerns, so each position has tradeoffs worth understanding.
Why Side Sleeping Works for Most People
Side sleeping checks the most boxes. It keeps the spine in a relatively neutral position, reduces snoring and airway obstruction, and supports healthy digestion. Research in the Journal of Neuroscience found that the brain’s waste-clearance system works most efficiently in the lateral (side) position compared to sleeping on the back or stomach. This system flushes out metabolic byproducts, including proteins linked to neurodegeneration, while you sleep.
For digestion, the left side has a slight edge. When you lie on your left, gravity keeps stomach acid below the esophagus, which reduces heartburn episodes. A study of 57 people with chronic heartburn found that acid cleared from the esophagus significantly faster when participants slept on their left side compared to their back or right side. The left-side position also supports the natural path of waste through the large intestine, from the ascending colon across to the descending colon, which can make morning bowel movements more regular.
The main downside of side sleeping is facial compression. Because one side of your face presses into the pillow for hours, side sleepers develop wrinkles on the forehead, lips, and cheeks over time. These “sleep wrinkles” run perpendicular to normal expression lines and can’t be treated with the same injections used for expression wrinkles, since they aren’t caused by muscle movement. For most people, this cosmetic tradeoff is minor compared to the health benefits.
Left Side vs. Right Side
If you have acid reflux or GERD, the left side is clearly better. Sleeping on the right side is associated with more frequent heartburn episodes because of how the stomach sits relative to the esophagus. During pregnancy, the left side is also the recommended position, especially in the third trimester. It allows the most blood flow to the baby and takes pressure off the inferior vena cava, the large vein that returns blood from the lower body to the heart. Lying on your back during late pregnancy can compress this vein and reduce circulation.
For people without reflux or pregnancy concerns, either side works well. Some people naturally alternate sides throughout the night, which is perfectly fine and may actually reduce sustained pressure on one shoulder or hip.
Back Sleeping: Good for Some, Risky for Others
Sleeping on your back distributes weight evenly across the widest surface of your body, which minimizes pressure points. It’s the best position for preventing facial wrinkles since nothing presses against your skin. If you have back pain, placing a pillow under your knees helps maintain the natural curve of your lower spine and relaxes the surrounding muscles. A small rolled towel under the waist can provide additional lumbar support.
The problem with back sleeping is airway obstruction. When you lie face-up, gravity pulls the tongue and soft tissues toward the back of the throat, narrowing the airway. For people with obstructive sleep apnea, the severity of breathing interruptions can double in the supine position compared to sleeping on the side. Even people without a sleep apnea diagnosis often snore more on their backs. If your partner reports loud snoring or you wake up feeling unrested, switching to your side is one of the simplest interventions to try.
Why Stomach Sleeping Causes Problems
Stomach sleeping is the least recommended position. It forces you to turn your head to one side to breathe, which puts your cervical spine in a rotated position for hours at a time. Pain specialists at the Hospital for Special Surgery describe it as the worst option for neck health because it makes a neutral spinal position impossible. Over years, this repeated strain can lead to spinal arthritis, narrowing of the spinal canal, and neurological symptoms like numbness, tingling, or weakness in the arms and hands.
If you can’t break the habit, placing a pillow under your hips and lower stomach reduces some of the strain on your lower back. You may also want to skip the head pillow entirely or use an extremely flat one to minimize the angle of neck rotation. But if you’re experiencing neck pain or stiffness, transitioning to side sleeping is worth the adjustment period.
Pillow Height by Position
The wrong pillow can cancel out the benefits of a good sleep position. The goal is always the same: keeping your head, neck, and spine in a straight line. But the height you need changes dramatically depending on how you sleep.
- Side sleepers need the tallest pillows, typically 10 to 14 cm (about 4 to 5.5 inches). The pillow fills the gap between your shoulder and your head. Broader-shouldered people need the higher end of that range, while smaller-framed sleepers do better around 10 to 11 cm. Firmer materials like memory foam or latex hold their height better under sustained pressure.
- Back sleepers need a medium-height pillow, around 7 to 10 cm (3 to 4 inches). A softer pillow works well here because it compresses under the weight of your head, cradling without pushing your chin toward your chest.
- Stomach sleepers should use a very flat pillow or none at all, staying under 7 cm. The goal is to minimize how much the neck has to rotate. A soft, compressible pillow is better than a firm one in this position.
Tips for Back Pain Relief
Your sleep position matters as much as your mattress when it comes to back pain. Side sleepers should draw their knees up slightly toward the chest and place a pillow between the legs. This keeps the hips, pelvis, and spine aligned and prevents the top leg from pulling the spine out of position. A full-length body pillow works well if a standard pillow shifts during the night.
Back sleepers benefit from a pillow under the knees, which takes tension off the lower back muscles and supports the lumbar curve. If you sleep on your stomach, a pillow under the hips tilts the pelvis enough to reduce compression on the lumbar spine, though this position still isn’t ideal for chronic back pain.
Switching Positions Takes Time
If you’ve identified that your current position is causing problems, changing it is possible but rarely instant. Most people take a few weeks to adjust. Pillows can help physically keep you in place: a body pillow along your back makes it harder to roll onto your back during the night, and a pillow between the knees encourages side sleeping by making the position more comfortable. Some people use a tennis ball sewn into the back of a sleep shirt to discourage back sleeping, a low-tech approach that sleep clinicians have used for decades with positional sleep apnea patients.
The position you wake up in matters more than the position you fall asleep in. You’ll shift throughout the night, and that’s normal. The goal is to spend the majority of your sleep time in a position that supports your breathing, your spine, and whatever health conditions are most relevant to you. For most people, that position is on the side, with the left side offering extra benefits for digestion and reflux.