For most people, side sleeping is the better choice. It keeps your airway open, reduces snoring, eases acid reflux, and may even help your brain clear waste more efficiently during the night. Back sleeping has its own advantages, particularly for spinal alignment and skin health, but it comes with enough downsides that sleep specialists generally favor the lateral position as a default recommendation.
That said, the best position depends on your body and your health. Someone with chronic shoulder pain will have a very different answer than someone who is pregnant or someone who snores. Here’s what the evidence says for each position, so you can make the call that fits your situation.
Why Side Sleeping Wins for Most People
Side sleeping is considered the optimal position for breathing. When you lie on your back, gravity pulls your tongue and the soft tissues in your throat backward, narrowing or blocking the airway. On your side, those tissues stay out of the way. This is why sleep specialists routinely tell patients with obstructive sleep apnea to avoid sleeping on their back. As one Harvard sleep medicine physician put it, all the soft tissue falls back “like a cork.” Even if you don’t have a diagnosed breathing disorder, side sleeping can significantly reduce snoring.
Side sleeping also has a clear edge for digestive comfort. The left side in particular discourages acid reflux by leveraging gravity and the natural anatomy of your stomach and esophagus. The American Gastroenterological Association specifically recommends left-side sleeping for people dealing with nighttime reflux. When you sleep on your back, stomach acid has an easier path into the esophagus, which is why reflux tends to worsen in that position.
There’s also intriguing evidence from neuroscience. A study published in the Journal of Neuroscience found that the brain’s waste-clearance system, which flushes out proteins linked to Alzheimer’s disease, works most efficiently in the lateral (side) position. In the study, side sleeping outperformed both back and stomach positions for clearing these waste products. The research was conducted in rodents and hasn’t been confirmed in humans yet, but it aligns with what we know about how sleep drives brain detoxification.
Where Back Sleeping Has the Advantage
Back sleeping does one thing better than any other position: it distributes your weight evenly and keeps your spine in a neutral line. There’s no twisting, no shoulder compression, no hip pressure points. People who sleep on their backs often wake up with less neck, back, and hip pain because the position takes stress off joints and muscles. If you’ve been dealing with morning stiffness or aches, switching to your back is worth trying.
Back sleeping is also the only reliable way to prevent sleep wrinkles. When you sleep on your side or stomach, your facial skin is subject to compression, shear, and stretching forces for hours at a time. Research has shown that these mechanical forces cause the skin to buckle, creating wrinkles that form in different patterns than expression lines. Over years, side sleeping can reinforce and deepen these creases. Dermatologists consistently recommend back sleeping to minimize this effect, though they also acknowledge it’s extremely difficult to change your sleep habits consciously.
When Your Health Condition Decides for You
Certain health situations make the choice straightforward. If you have sleep apnea, your doctor will almost certainly tell you to sleep on your side. People with heart failure or lung conditions, or those carrying extra weight around the midsection, often feel short of breath on their back because the position makes it harder for the lungs to fully expand. It can feel, as one specialist described it, like someone sitting on your chest.
Heart failure adds another layer of complexity. Many people with this condition find that sleeping on the left side worsens their shortness of breath, so they gravitate toward the right side instead. If you have heart failure, pay attention to which side feels more comfortable and discuss positioning with your cardiologist.
Pregnancy makes the decision clear-cut. Starting at 28 weeks, pregnant patients should avoid falling asleep on their back. A meta-analysis found that going to sleep in the supine position was associated with a significantly higher risk of stillbirth compared to the left-side position. Supine sleeping was also linked to a higher likelihood of delivering a smaller baby. The American College of Obstetricians and Gynecologists recommends side sleeping, particularly on the left, because it promotes optimal blood flow to the uterus and reduces swelling in the legs and ankles.
The Downsides of Side Sleeping
Side sleeping isn’t perfect. Your spine isn’t naturally well-aligned in this position, and pressure can concentrate on whichever shoulder and hip are bearing your weight. If you consistently sleep on the same side, you may develop shoulder pain or hip soreness over time. Falling asleep on one arm can compress nerves, leaving you with that tingling numbness when you wake up.
For people who already have shoulder problems, side sleeping can aggravate the issue considerably. Orthopedic specialists often recommend switching to back sleeping to take pressure off the shoulder joint. If that’s not realistic, alternating sides throughout the night and using supportive pillows can help.
How to Support Either Position
Whichever position you choose, pillow placement makes a big difference in how your body feels the next morning.
- 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 your top leg from pulling your lower back out of position. A full-length body pillow works well if you tend to shift around. Your head pillow should be thick enough to fill the gap between your ear and the mattress so your neck stays straight.
- Back sleepers: Place a pillow under your knees to relax your lower back muscles and maintain the natural curve of your lumbar spine. A small rolled towel under your waist can provide additional support. Your head pillow should keep your neck aligned with your chest and back, not propped up at a steep angle.
How to Train Yourself Into a New Position
If you’ve decided to switch positions, expect it to feel awkward for a while. Most people shift positions dozens of times per night without realizing it, so the goal isn’t to stay perfectly still. It’s to change which position you fall asleep in and return to when you half-wake during the night.
The most well-known technique for people trying to stop back sleeping is the tennis ball method: sew a tennis ball into the back of a sleep shirt so rolling onto your back becomes uncomfortable. It sounds crude, but it works, and it’s a form of what sleep specialists call positional therapy. Wearable devices designed for the same purpose are also available and tend to be more comfortable. Placing a firm pillow behind your back while side sleeping can act as a physical barrier that keeps you from rolling over. For people trying to stay on their back, a pillow on each side of the torso can provide a similar guardrail effect.
Give yourself a few weeks. Sleep habits are deeply ingrained, and your body will resist the change at first. Most people find that consistent pillow placement and a physical cue (like the tennis ball or a body pillow) are enough to retrain their default position over time.