There is no single best sleeping position for everyone. The right choice depends on your body and what you’re dealing with, whether that’s back pain, acid reflux, snoring, or pregnancy. Side sleeping is the most common position by far, and it offers the broadest range of benefits for most people. Adults spend about 54% of their time in bed on their side, 38% on their back, and less than 8% on their stomach.
Here’s what the evidence says about each position and when one clearly wins over the others.
Side Sleeping Works Best for Most People
Side sleeping is the default human sleep posture, and there’s a good reason it evolved that way. Research published in the Journal of Neuroscience found that the brain’s waste-clearance system works most efficiently in the lateral (side) position. During sleep, your brain flushes out metabolic byproducts, including proteins linked to Alzheimer’s disease. This cleanup process was significantly more effective in the side position compared to sleeping on the stomach, and modestly better than sleeping on the back.
Side sleeping also keeps your airway more open than back sleeping. In people with obstructive sleep apnea, the number of breathing disruptions per hour drops dramatically when switching from back to side. Back sleeping produced an average of about 60 events per hour in one study, while side sleeping cut that roughly in half. Even if you don’t have a diagnosed sleep disorder, sleeping on your side can reduce snoring for the same reason: gravity isn’t pulling your tongue and soft palate into the airway.
If you sleep on your side, place a pillow between your knees. This keeps your spine, pelvis, and hips aligned and takes pressure off your lower back. Draw your legs up slightly toward your chest for additional comfort. Your pillow should be high enough to fill the gap between your ear and the mattress so your neck stays straight. Most standard pillows are actually too low for side sleeping. Research on ergonomic pillow design suggests side sleepers need around 12 to 14 centimeters of loft (roughly 5 to 6 inches), depending on shoulder width.
Left Side vs. Right Side
Which side matters more than you might expect. For acid reflux, the left side is clearly better. When you lie on your left, the junction between your esophagus and stomach sits above the level of stomach acid, making it harder for acid to creep upward. A systematic review found that left-side sleeping significantly reduced both acid exposure time and the total number of reflux episodes compared to lying on the right side or on the back.
For sleep apnea, though, the right side has a slight edge. Research comparing breathing disruptions on each side found that right-side sleeping produced fewer apnea events than left-side sleeping in people with moderate or severe sleep apnea (about 24 events per hour on the right vs. 30 on the left). The difference wasn’t significant for mild cases.
If you have both reflux and apnea, the left side is generally the better compromise since positional therapy for apnea focuses mainly on avoiding your back.
Back Sleeping Has Specific Advantages
Sleeping on your back distributes your body weight evenly across the widest surface area, which minimizes pressure points. It’s the best position for keeping your spine in a neutral alignment without needing to worry about shoulder compression or hip pressure. If you have shoulder pain from a rotator cuff injury, tendonitis, or arthritis, back sleeping with your arms resting at your sides is the preferred position because it avoids direct pressure on the joint.
Back sleeping is also the only position that keeps your face completely off the pillow. Side and stomach sleepers press their skin against the pillow for hours, which over time contributes to “sleep wrinkles,” distinct from expression wrinkles. Research has documented visible facial deformities from habitual side sleeping, including deepened lines around the mouth, crow’s feet, and flattening of the forehead on the side that contacts the pillow. If preventing premature facial aging matters to you, back sleeping is the clear winner.
The catch is that back sleeping is the worst position for snoring and sleep apnea. Gravity pulls the tongue backward, narrowing the airway. It’s also not recommended during pregnancy, particularly after 28 weeks, because the weight of the uterus compresses the inferior vena cava, the large vein that returns blood from your lower body to your heart. This can reduce blood flow to both you and the baby.
If you do sleep on your back, place a pillow under your knees to maintain the natural curve of your lower back and reduce strain on the lumbar spine. A pillow height of about 7 to 10 centimeters (3 to 4 inches) works well for back sleepers to keep the neck in alignment with the chest and spine.
Stomach Sleeping Creates the Most Problems
Stomach sleeping is the least common position and the one with the fewest benefits. It forces your head to turn to one side for hours, which strains the neck and can compress nerves. Your lower back also tends to sag into the mattress without support, exaggerating the lumbar curve. The brain’s waste-clearance system performs worst in the prone position as well, with slower clearance and more retention of metabolic waste compared to both side and back sleeping.
The one advantage of stomach sleeping is that, like side sleeping, it keeps the airway relatively open and can reduce snoring. But the neck and back tradeoffs make it a poor long-term choice. If you can’t break the habit, a very thin pillow (or no pillow) under your head and a flat pillow under your hips can reduce some of the spinal strain.
Best Positions for Common Conditions
- Low back pain: Side sleeping with a pillow between the knees, or back sleeping with a pillow under the knees. Both keep the spine neutral and reduce pressure on the lumbar discs. A small rolled towel under the waist adds extra support for back sleepers.
- Acid reflux or GERD: Left side. This position reduces acid exposure time and reflux events more effectively than any other posture.
- Snoring or sleep apnea: Either side, with a slight advantage to the right side for moderate to severe apnea. Avoid sleeping on your back.
- Shoulder pain: Back sleeping with arms at your sides. If that’s uncomfortable, sleep on the opposite side and hug a pillow to keep the sore shoulder slightly forward and supported.
- Pregnancy (after 28 weeks): Left side. This position maximizes blood flow to the baby and improves kidney function. Avoid lying flat on your back.
- Neck pain: Back sleeping with a pillow that supports the natural cervical curve, or side sleeping with a pillow high enough to keep the head level with the spine. Avoid stomach sleeping.
How to Change Your Sleep Position
Most people shift positions multiple times throughout the night, so you won’t stay perfectly in one spot. The goal is to fall asleep in your target position and set up your pillows so that when you do move, you’re guided back. A body pillow along your back can discourage rolling onto your back if you’re trying to stay on your side. Tennis balls sewn into the back of a sleep shirt are an old but effective trick for the same purpose.
Changing a lifelong sleep habit takes time. Your body will default to what’s familiar, especially once you’re deeply asleep. Give yourself two to four weeks of consistent effort before deciding whether a new position works for you. The pillow setup matters as much as the position itself. A side sleeper using a flat pillow will wake up with neck pain regardless of how good the position is in theory, and a back sleeper without knee support will still strain their lower back.