Side sleeping is the best position for most people. It keeps your airway open, supports spinal alignment when done correctly, and may even help your brain clear waste more efficiently during the night. But the “proper” position depends partly on your body and what health issues you’re managing. Back sleeping wins for spinal neutrality, left-side sleeping is best for acid reflux, and stomach sleeping is the one position most experts recommend avoiding.
Why Side Sleeping Works for Most People
About 65% of people naturally sleep on their side, and there are good reasons for that. Side sleeping keeps the airway open by preventing the tongue and soft tissues from collapsing toward the back of the throat. This reduces snoring and helps with sleep apnea, since more than half of all obstructive sleep apnea cases are most severe when a person lies face-up.
Animal research published in the Journal of Neuroscience found that the brain’s waste-clearance system works most efficiently in the lateral (side) position compared to back or stomach sleeping. During sleep, the brain flushes out metabolic waste, including proteins linked to neurodegenerative disease. Side-sleeping animals cleared these waste products significantly faster than those in other positions. This hasn’t been confirmed in humans yet, but it aligns with the fact that side sleeping is the natural resting posture for most mammals.
The trade-off is pressure. Lying on your side can concentrate force on your shoulder, hip, and the side of your neck. People with shoulder injuries often can’t tolerate sleeping on the affected side. And if you fall asleep with your arm pinned underneath you, expect numbness when you wake up.
Left Side vs. Right Side
If you deal with heartburn or acid reflux, the left side is clearly better. When you lie on your left, your stomach sits below your esophagus, making it harder for acid to travel upward. Research from Amsterdam UMC also found that stomach acid drains back from the esophagus to the stomach more quickly in this position. Sleeping on the right side or flat on your back does the opposite, letting acid pool where it shouldn’t.
Left-side sleeping is also the recommended position during pregnancy. The American College of Obstetricians and Gynecologists advises sleeping on your side during the second and third trimesters, ideally with one or both knees bent. This promotes blood flow to the uterus and reduces swelling in the legs and ankles. A pillow between the knees and another under the belly can make this position more comfortable. Back sleeping in later pregnancy is discouraged because the weight of the growing uterus presses on the spine and major blood vessels.
Back Sleeping: Best for Your Spine
If you wake up with neck, back, or hip pain, sleeping on your back may help. This position distributes your weight evenly and eliminates the sideways forces on your spine that side sleeping creates. For most people, it’s the most neutral alignment you can achieve while lying down.
The key adjustment: place a pillow under your knees. This relaxes the muscles along your lower back and preserves its natural curve. If you still feel a gap between your lower back and the mattress, a small rolled towel tucked under your waist adds extra support. Your head pillow should keep your neck aligned with your chest and back, not pushed forward or tilted.
Back sleeping does have real downsides, though. It’s the worst position for snoring and sleep apnea because gravity pulls the tongue and soft palate toward the airway. People with breathing difficulties often describe the sensation as someone sitting on their chest. It also worsens acid reflux, since lying flat gives stomach acid an easy path into the esophagus.
Why Stomach Sleeping Causes Problems
Stomach sleeping is the one position that most sleep and orthopedic experts recommend against. Only about 5% of people sleep this way, and the mechanics explain why it’s problematic.
To breathe while face-down, you have to turn your head to one side. Holding your neck in that rotated position for hours creates strain on the cervical spine. Over time, this can limit your neck’s range of motion. There’s also a tendency to tuck your arms under your head or body, which compresses nerves and strains the elbows and shoulders. Meanwhile, your lower back sags into the mattress without support, flattening the natural lumbar curve.
If you can’t break the habit, the Mayo Clinic recommends placing a pillow under your hips and lower stomach to reduce the arch in your lower back. Use either a very thin pillow for your head or skip it entirely, since a thick pillow forces your neck into an even steeper angle.
How to Set Up Your Pillow Correctly
The right pillow height depends entirely on your sleeping position. The goal is neutral alignment: your ears level with your shoulders, your chin parallel to the floor, and your neck following the gentle curve of your spine without excessive arching or flattening.
- Side sleepers: 4 to 6 inches of thickness. The pillow needs to fill the gap between your ear and the mattress so your head doesn’t tilt downward.
- Back sleepers: 3 to 5 inches. Too thick and your chin pushes toward your chest. Too thin and your head drops back.
- Stomach sleepers: Under 2 to 3 inches, or no pillow at all. Anything thicker forces your neck into extension.
For side sleepers with back pain, adding a second pillow between your knees keeps your hips, pelvis, and spine aligned. Drawing your legs up slightly toward your chest (a loose fetal position) helps as well. A full-length body pillow can serve both purposes at once.
Sleep Wrinkles Are Real
This one surprises most people. Research published in the Aesthetic Surgery Journal found that pressing your face against a pillow night after night creates wrinkles that are distinct from the expression lines caused by smiling or squinting. These “sleep wrinkles” form from compression, tension, and shear forces on the skin, and they typically show up on the forehead, lips, and cheeks.
They get worse with age as skin thins and loses elasticity, and they can’t be treated with injections that relax muscles, because muscles aren’t the cause. The only real prevention is sleeping on your back, which keeps your face free from contact with the pillow. For most people, this is a cosmetic consideration that ranks well below breathing and spinal health. But if you’re already a back sleeper, it’s one more benefit of staying that way.
Choosing the Right Position for You
There’s no single “correct” sleeping position that works for everyone. The best approach is to match your position to whatever health concern matters most to you right now.
- Snoring or sleep apnea: Side sleeping, either side.
- Acid reflux: Left side.
- Lower back or hip pain: Back sleeping with a pillow under the knees, or side sleeping with a pillow between the knees.
- Shoulder pain: Back sleeping, or side sleeping on the unaffected side.
- Pregnancy (second and third trimesters): Left side with knee and belly support.
- Skin aging concerns: Back sleeping.
Most people shift positions multiple times during the night, and that’s normal. Starting in your preferred position and using pillows strategically to maintain alignment gives you the best chance of staying comfortable through to morning. If you’re trying to switch away from stomach sleeping, placing a body pillow against your front can discourage you from rolling over while still giving you something to rest against.