Side sleeping is the best position for most people. It keeps your spine naturally aligned, keeps your airway open, and helps your brain clear waste more efficiently than other positions. Adults already spend about 54% of their sleep time on their side, 38% on their back, and 7% on their stomach, suggesting the body gravitates toward what works best.
That said, the “right” position depends on what your body needs. Back sleeping is better for preventing wrinkles. Left-side sleeping is better for acid reflux. And certain health conditions can make one position clearly superior to another.
Side Sleeping: The Best All-Around Position
Side sleeping checks more boxes than any other position. It maintains the spine’s natural curve, reduces snoring, and keeps the airway from collapsing the way it can when you’re flat on your back. For people with obstructive sleep apnea, the difference is dramatic: a meta-analysis found that simply avoiding the back position reduced breathing disruptions by 54% and improved blood oxygen levels.
Your brain also benefits. 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. In animal studies, this clearance was significantly faster when subjects slept on their sides compared to their stomachs, and somewhat faster than on their backs. The researchers suggested that side sleeping may have evolved specifically to optimize this cleaning process.
To get the most from side sleeping, place a pillow between your knees. This prevents your top leg from pulling your spine out of alignment and reduces pressure on your lower back and hips. A pillow with a medium or high loft (roughly 5.5 to 7.5 inches) works best for side sleepers because it fills the gap between your shoulder and head, keeping your neck straight.
Left Side vs. Right Side
For most people, either side is fine. But two specific conditions tip the balance.
If you deal with acid reflux or GERD, sleep on your left side. The stomach sits below the esophagus in this position, making it harder for acid to travel upward. Research from Amsterdam UMC also found that when acid does reach the esophagus, it drains back into the stomach more quickly on the left side.
If you have heart failure, you may naturally prefer the right side. A study in the Journal of the American College of Cardiology found that heart failure patients spent twice as long on their right side compared to their back or left side. The right-side position appeared to normalize stress signals from the heart’s nervous system, acting as a kind of self-protective mechanism.
Back Sleeping: Best for Skin, Tricky for Breathing
Sleeping on your back distributes weight evenly and keeps your face off the pillow, which matters more than most people realize. Stomach and side sleeping press your skin into the pillow for hours, creating compression wrinkles on the forehead, cheeks, and lips that deepen over time. Unlike expression lines, these wrinkles aren’t caused by muscle movement, so treatments like Botox don’t help. Back sleeping is the only position that avoids this facial compression entirely.
Back sleeping also works well for spinal health when done correctly. Place a pillow or rolled towel under your knees to prevent your lower back from arching excessively. Use a mid-loft pillow (around 5.5 to 6.5 inches) that supports your head without pushing it forward.
The major downside: sleeping on your back 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. In people with positional sleep apnea, breathing disruptions on the back are at least twice as frequent as in any other position, and the events themselves are more severe, with deeper drops in oxygen and longer interruptions. If you snore heavily or have been told you stop breathing in your sleep, back sleeping is worth avoiding.
Stomach Sleeping: The Position to Minimize
Stomach sleeping is the least recommended position, and only about 7% of sleep time is spent this way. It forces your head to turn sharply to one side for hours, straining the neck and upper spine. It also flattens the natural curve of your lower back, which can lead to stiffness and pain over time.
Brain waste clearance is also at its worst in this position. The animal studies on glymphatic transport found that the prone position, where the head is more upright, led to slower clearance and more retention of metabolic waste compared to side or back sleeping.
If you can’t break the habit, a thin pillow under your pelvis or lower abdomen helps keep your hips supported and reduces the arch in your lower back. Use a very flat pillow for your head, or none at all, to minimize neck rotation. But if you’re experiencing neck pain or morning headaches, transitioning to side sleeping is worth the effort.
Sleep Position During Pregnancy
In late pregnancy, side sleeping is strongly recommended, with the left side being ideal. The left side allows maximum blood flow to the baby and placenta. Lying on your back puts the weight of the uterus directly on the inferior vena cava, a major vein that returns blood from your lower body to your heart. This pressure can reduce circulation, lower blood pressure, and cause dizziness.
A pillow between the knees and another supporting the belly can make side sleeping more comfortable as pregnancy progresses.
How to Match Your Pillow to Your Position
The wrong pillow can undo the benefits of a good sleep position. The goal is always the same: keep your head, neck, and spine in a straight line.
- Side sleepers need a higher pillow (5.5 to 7.5 inches) to bridge the space between the shoulder and ear. Too flat, and your head tilts down. Add a knee pillow to keep hips aligned.
- Back sleepers do best with a medium pillow (around 5.5 to 6.5 inches). It should cradle the natural curve of your neck without pushing your chin toward your chest. A knee pillow or rolled towel under the knees helps here too.
- Stomach sleepers should use the thinnest pillow possible, or skip it entirely, to reduce the angle of neck rotation.
Changing Your Sleep Position
People shift positions roughly 20 times per night, and that number decreases with age, dropping from about 27 shifts per night in younger adults to 16 in older adults. Your starting position is the only one you can consciously control, but it does influence where you spend most of the night.
If you’re trying to stop sleeping on your back (for snoring or apnea), placing a tennis ball in a pocket sewn to the back of a sleep shirt is a classic approach that works for many people. Positional therapy devices and specially shaped pillows can also help. If you’re trying to switch from stomach to side sleeping, a body pillow gives you something to drape your arm and leg over, mimicking the feeling of lying face down while keeping you on your side.
Perfect consistency isn’t realistic, and it isn’t necessary. Starting in a better position and spending more of the night there is enough to make a meaningful difference for your back, your breathing, and your long-term health.