Side sleeping, particularly on your left side, is the healthiest position for most people. It keeps your airways open, supports digestion, and may even help your brain clear waste more efficiently during the night. That said, the best position depends on your body and any conditions you’re dealing with, so the full picture is worth understanding.
Why Side Sleeping Comes Out on Top
Side sleeping checks the most boxes for the widest range of people. It naturally keeps your airway open, which reduces snoring and can ease mild sleep apnea. It’s also the position your body probably gravitates toward already, since most adults spend the majority of the night on one side or the other.
There’s also a compelling brain health angle. A study published in The Journal of Neuroscience found that the brain’s waste-clearance system works most efficiently in the lateral (side-lying) position. This system flushes out metabolic byproducts during sleep, including amyloid-beta, a protein linked to Alzheimer’s disease. The researchers found that side sleeping outperformed both back and stomach positions for this clearance process. The study was conducted in rodents, so the finding still needs confirmation in humans, but it aligns with the fact that side sleeping is the most common natural sleep posture across many species.
The main downside of side sleeping is facial pressure. Pressing your face into a pillow night after night can cause creases and, over time, contribute to skin changes or breakouts on the contact side.
Left Side vs. Right Side
If you sleep on your side, the left side has a slight edge for digestive health. The American Gastroenterological Association recommends left-side sleeping for people with acid reflux or GERD. The reason is anatomical: when you lie on your left, gravity and the natural position of your stomach relative to your esophagus work together to keep acid from creeping upward. Sleeping on your right side can actually make reflux worse.
There’s one exception. People with heart failure often find that left-side sleeping worsens shortness of breath, because the heart rests more directly against the chest wall in that position. If you have heart failure, sleeping on your right side tends to feel more comfortable and may be the better choice.
Back Sleeping: Great for Some, Risky for Others
Sleeping on your back distributes your weight evenly and can be excellent for low back pain. Many people find it helpful because it allows the spine to rest in a relatively neutral position without twisting. It’s also the best position for your skin, since nothing is pressing against your face all night.
The trade-off is that back sleeping is the worst position for snoring and sleep apnea. Gravity pulls the tongue and soft tissues toward the back of the throat, narrowing the airway. If your partner has mentioned that you snore loudly or you wake up feeling unrested, back sleeping could be making things worse. Back sleeping can also aggravate neck pain for some people, so it’s not a universal fix for spinal issues.
Why Stomach Sleeping Is the Least Recommended
Stomach sleeping is consistently ranked as the least healthy position. The core problem is your neck: to breathe, you have to turn your head to one side, which forces your cervical spine into a sustained twist for hours. This compresses joints, increases muscle tension, and can irritate nerves. Morning neck stiffness and headaches are common complaints among stomach sleepers.
It also flattens the natural curve of your lower back, which can lead to or worsen lumbar pain over time. The brain-waste clearance research mentioned earlier found that the prone (stomach-down) position was the least efficient of all three positions, with slower clearance and more retention of waste products.
The one point in stomach sleeping’s favor: like side sleeping, it keeps the airway relatively open and can reduce snoring. But the neck and back costs generally outweigh that single benefit.
How to Optimize Your Position With Pillows
The right pillow setup can turn a good position into a great one, or make a less-than-ideal position more tolerable.
- Side sleepers need a thicker pillow that fills the gap between the head and the mattress, keeping the head aligned on an even plane with the spine. A thin pillow lets your head drop, straining the neck. Place a small pillow or rolled-up towel between your knees to keep your hips, pelvis, and spine aligned and relieve pressure on the hip joint.
- Back sleepers should use a medium-loft pillow, high enough to cushion the neck but not so thick that it pushes the chin toward the chest. Placing a pillow under your knees helps relax the back muscles and maintain the natural curve of the lower back. A small rolled towel under the waist can add extra support if needed.
- Stomach sleepers who can’t switch positions can reduce strain by placing a pillow under the hips and lower abdomen, which helps prevent the lower back from sagging. Use a very flat pillow for your head, or skip one entirely, to minimize the angle of neck rotation.
Sleep Position During Pregnancy
You’ve probably heard that sleeping on your left side is essential during the third trimester, and that back sleeping increases the risk of stillbirth. The reality is more nuanced than the headlines suggest. Experts at the University of Utah Health point out that there isn’t enough data to conclude that back sleeping directly causes stillbirth. The link, to the extent it exists, may actually be driven by sleep apnea, which worsens in the back position, rather than the position itself.
Left-side sleeping is still a reasonable default during late pregnancy because it promotes blood flow to the uterus. But the stress of trying to maintain an unnatural position all night may do more harm than the position you’d naturally settle into. If you wake up on your back, there’s no reason to panic. Simply roll to your side and go back to sleep.
Switching Positions Takes Time
If you want to transition from stomach to side sleeping, or from one side to the other, expect it to feel awkward for a few weeks. Your body has spent years building a habit, and it won’t change overnight. A body pillow can help side sleepers stay in place by giving you something to rest an arm and leg over, which also prevents you from rolling onto your stomach. Some people place a tennis ball in a pocket sewn to the front of a sleep shirt to discourage stomach rolling.
The most important factor is still sleep quality. A position that keeps you tossing and awake all night is worse than a less-than-ideal position that lets you sleep deeply. Start with small adjustments, like adding a knee pillow or switching pillow thickness, before overhauling your entire sleep posture.