Side sleeping is widely considered the healthiest sleep position, and it’s already the most popular one. More than 60% of adults naturally sleep on their side. This preference may not be a coincidence: research suggests the lateral position offers measurable advantages for brain health, digestion, and breathing compared to sleeping on your back or stomach.
That said, the “best” position depends partly on your body and health concerns. Here’s what the evidence shows for each position and how to optimize whichever one works for you.
Why Side Sleeping Comes Out on Top
The strongest argument for side sleeping involves your brain’s waste-removal system. During sleep, the spaces between brain cells expand, allowing cerebrospinal fluid to flush out metabolic waste, including a protein called beta-amyloid that accumulates in Alzheimer’s disease. A study published in the Journal of Neuroscience found that this cleanup process, known as glymphatic transport, was most efficient in the lateral (side) position compared to sleeping on the back or stomach. In the prone (stomach) position, the researchers observed slower clearance and more retention of waste products in the brain.
Side sleeping also keeps your airway more open. People with obstructive sleep apnea experience significantly worse episodes when lying on their back. On polysomnography tests, the number of breathing interruptions per hour can be twice as high in the supine position compared to the lateral position. The duration of those pauses, the drops in blood oxygen, and the severity of heart rate changes are all measurably worse on the back. Even people without a diagnosed sleep disorder tend to snore less on their side because gravity isn’t pulling the tongue and soft tissues backward into the airway.
Left Side vs. Right Side
If you sleep on your side, the left side has a specific advantage for acid reflux. When you lie on your left, the esophagus and the muscular ring that separates it from the stomach sit higher than the stomach itself. This means stomach acid drains away from the esophagus more quickly. Lying on the right side or back reverses this geometry, allowing acid to pool near the esophageal opening. If you deal with heartburn or GERD symptoms at night, switching to your left side is one of the simplest changes you can make.
For people without reflux issues, either side works well. The brain-health and breathing benefits apply to both lateral positions equally.
When Back Sleeping Makes Sense
Back sleeping has one clear advantage: your skin. When you sleep on your side or stomach, your face presses into the pillow for hours, creating compression wrinkles over time. These wrinkles typically show up on the forehead, lips, and cheeks, and they run perpendicular to normal expression lines. Unlike wrinkles caused by smiling or squinting, compression wrinkles can’t be treated with Botox because they aren’t caused by muscle movement. Sleeping on your back eliminates this mechanical pressure entirely.
Back sleeping also distributes your body weight evenly across the widest surface area, which can reduce pressure points. For people with certain types of back pain, placing a pillow under the knees while lying face-up helps relax the lower back muscles and maintain the spine’s natural curve.
The downsides are notable, though. Back sleeping is the worst position for snoring and sleep apnea, and it worsens acid reflux. If you don’t have those issues and care about skin aging, it’s a reasonable choice.
Stomach Sleeping: The Position to Avoid
Stomach sleeping is the least recommended position, and only about 5% of adults prefer it. The core problem is your neck. Sleeping face-down forces you to turn your head to one side to breathe, which stretches the muscles on one side of the neck while compressing the other. Hold that position for six to eight hours and you have a recipe for waking up stiff and sore. It’s the most common cause of neck pain related to sleep posture.
Prone sleeping also performed worst for brain waste clearance in the Journal of Neuroscience study, and it creates the same facial compression wrinkles as side sleeping. If you’re a lifelong stomach sleeper, transitioning to your side is the most natural shift since both positions involve a similar degree of body rotation.
Sleep Position During Pregnancy
After 28 weeks of pregnancy, going to sleep on your side can halve the risk of stillbirth compared to falling asleep on your back. The reason is straightforward: lying on your back in late pregnancy compresses major blood vessels, reducing blood flow to the uterus and oxygen delivery to the baby. Either side is fine, left or right, whichever feels more comfortable. This applies to daytime naps as well.
If you wake up on your back during the night, there’s no need to panic. Just roll to your side and fall back asleep. The key is the position you settle into when you drift off, since that’s where you spend the longest uninterrupted stretch.
How to Optimize Your Position With Pillows
The right pillow setup matters almost as much as the position itself. Poor alignment can cancel out the benefits of an otherwise healthy posture.
- Side sleepers: Draw your legs up slightly toward your chest and place a pillow between your knees. This keeps your spine, pelvis, and hips aligned and prevents the top leg from pulling your lower back out of position. Your head pillow should be thick enough to fill the gap between your shoulder and ear, keeping your neck straight rather than angled up or down.
- Back sleepers: Place a pillow under your knees to maintain the natural curve of your lower back. Use a relatively thin head pillow so your neck stays in line with your chest and spine rather than being pushed forward.
- Stomach sleepers: If you can’t switch positions, use the thinnest pillow possible (or none at all) to minimize the angle your neck has to turn. A flat pillow under the hips can reduce lower back strain.
In all positions, your pillow should keep your neck aligned with your chest and back. A pillow that’s too high or too flat forces your cervical spine into an unnatural angle, which is a common source of morning stiffness regardless of how you sleep.
Changing Your Sleep Position
Most people shift positions multiple times during the night, so total control isn’t realistic. What you can influence is the position you fall asleep in, since you tend to spend the majority of your time there. If you want to transition from stomach to side sleeping, placing a body pillow along your front can give you something to lean into, mimicking the feeling of being face-down without the neck rotation. Tennis balls taped to the front of a shirt are a cruder but effective deterrent.
For people trying to avoid back sleeping due to snoring or apnea, the same tennis ball trick works on the back of a shirt. Positional therapy devices that vibrate when you roll onto your back are also available and tend to be more comfortable long-term. Most people can retrain their default position within a few weeks of consistent effort.