For most people, the left side is the better side to sleep on. It reduces acid reflux, supports digestion, and keeps your airway more open than sleeping on your back. That said, the “best” side depends on your body and any health conditions you’re dealing with. Some people genuinely do better on the right.
Why the Left Side Wins for Digestion
Your stomach sits slightly to the left of your midline, and its natural curve means that when you lie on your left side, gravity keeps stomach acid pooled away from the opening to your esophagus. Research from Amsterdam UMC confirmed that patients sleeping on their left side had less acid in their esophagus compared to sleeping on their right side or their back. Even when acid did creep up, it drained back into the stomach faster in the left-side position.
Sleeping on your right side does the opposite. It relaxes the muscular valve connecting the stomach and esophagus, making it easier for acid to escape upward. If you deal with heartburn or gastroesophageal reflux, switching to your left side at night is one of the simplest changes you can make. Many people notice a difference within the first few nights.
For general digestion beyond reflux, the left side also helps waste move from the small intestine into the large intestine with the help of gravity, following the natural path of your digestive tract.
When the Right Side Is Better
People with heart failure often find that sleeping on the left side makes their shortness of breath worse. The American Heart Association notes that many heart failure patients naturally prefer sleeping on their right side for this reason. If you have a heart condition and notice more discomfort or breathlessness on your left, the right side is the better choice for you.
There’s no strong evidence that healthy people without heart conditions need to worry about cardiac pressure from left-side sleeping. But if you’ve been told you have an enlarged heart or congestive heart failure, pay attention to which side feels more comfortable breathing-wise and mention it to your cardiologist.
Side Sleeping and Snoring
If snoring or sleep apnea is your main concern, the specific side matters less than simply not sleeping on your back. Back sleeping lets gravity pull the tongue and soft tissues backward, partially blocking the airway. A meta-analysis of positional therapy studies found that switching from back sleeping to side sleeping reduced breathing interruptions by about 54% on average. Some individuals in those studies saw reductions of 70% or more.
Either side works for this purpose. The key is staying off your back throughout the night, which is harder than it sounds. Positional devices worn on the neck or forehead that vibrate when you roll onto your back have shown real results in clinical testing, reducing back-sleeping time by roughly a third and meaningfully improving breathing scores.
Sleep Position During Pregnancy
In the third trimester, most guidelines suggest sleeping on your side rather than your back. The concern is that a growing uterus can press on major blood vessels when you lie flat, potentially reducing blood flow. A British study linked back sleeping in late pregnancy with a higher risk of stillbirth, though experts at the University of Utah Health caution that the evidence isn’t strong enough to draw firm conclusions.
The left side is traditionally recommended because it takes pressure off the large vein that returns blood from your lower body to your heart. That said, the practical advice from most OB-GYNs is straightforward: sleep on whichever side is comfortable, and don’t feel guilty if you wake up on your back. Your body will typically shift you before there’s any real problem.
Protecting Your Shoulders and Spine
Side sleeping does put sustained pressure on the shoulder you’re lying on, and over months or years, this can compress tendons, irritate the rotator cuff, or inflame the fluid-filled sacs (bursae) that cushion the joint. If you already have shoulder pain, avoid sleeping on that side entirely. Sleep on the opposite side and place a pillow in front of your body so your top arm rests on it, keeping the sore shoulder slightly elevated and decompressed.
One common mistake is tucking your bottom arm under your pillow or body. This forces the shoulder into an unnatural position for hours and increases inflammation. Keep your bottom arm in front of you or at your side instead.
Pillow height matters more for side sleepers than any other position. You need enough loft to fill the gap between your ear and the mattress so your neck stays in a straight line with your spine. A good check: your ear should be level with your shoulder. Most side sleepers do well with a pillow five to seven inches high, though broader shoulders need more height. A pillow that’s too thin lets your head tilt downward, straining neck muscles. Too thick, and your head tilts upward, creating the same problem in the other direction.
Placing a second pillow between your knees keeps your hips aligned and reduces lower back strain. This is especially helpful if you have any hip or lumbar pain.
What Side Sleeping Does to Your Skin
There is a cosmetic trade-off. Side sleeping is the most common position (about 65% of sleep time for most people), and the sustained compression against a pillow creates “sleep wrinkles” on the forehead, cheeks, and lips over time. These wrinkles run in different directions than expression lines, and because they’re caused by mechanical pressure rather than muscle movement, treatments like Botox don’t help with them.
The Aesthetic Society notes that sleeping on your back is the only position that avoids facial compression entirely, but also acknowledges that consciously changing your sleep position is extremely difficult. If this concerns you, silk or satin pillowcases reduce friction, and some specialty pillows are designed to cradle the face with less direct pressure. But for most people, the health benefits of side sleeping outweigh the cosmetic effects.
Choosing Your Side
If you’re generally healthy, the left side offers the most benefits: better digestion, less reflux, and good airway positioning. If you have heart failure or left-shoulder pain, the right side is your better option. For snoring and sleep apnea, either side is a significant improvement over your back. And if you’re pregnant, any side position is preferable to flat on your back in the third trimester.
Most people shift positions multiple times during the night, and that’s perfectly normal. Starting on your preferred side and setting yourself up with the right pillow height and support gives you the best chance of staying there through the deeper phases of sleep, which is when position matters most.