For most people, sleeping on your left side offers the widest range of health benefits. It reduces acid reflux, supports digestion, and may help your brain clear waste more efficiently during sleep. That said, the best side depends on your specific health situation. People with heart failure, for example, often do better on their right side. More than 60% of adults already sleep on their side naturally, so if that’s you, a few adjustments can make the position even better.
Why the Left Side Wins for Most People
The left side gets the strongest recommendation because of simple anatomy. Your stomach sits slightly to the left of your body’s midline, and its main opening (where it connects to the esophagus) sits near the top. When you lie on your left side, the esophagus and the muscle ring that keeps stomach acid in place are positioned higher than the stomach itself. Acid drains away from that opening rather than pooling near it. This makes left-side sleeping particularly helpful if you deal with heartburn or gastroesophageal reflux.
When you sleep on your right side, the stomach sits above that junction, making it easier for acid to creep upward into the esophagus. If you’ve ever noticed that reflux feels worse on one side than the other, this is why.
Brain Waste Clearance During Sleep
Your brain has its own waste-removal system that becomes most active while you sleep. It flushes out metabolic byproducts, including proteins linked to Alzheimer’s disease. A study published in the Journal of Neuroscience found that this cleaning process was most efficient when subjects were in a lateral (side) position compared to sleeping on the back or stomach. Both left and right side sleeping outperformed stomach sleeping for waste clearance, so the benefit here isn’t about picking a specific side. It’s about sleeping on your side at all rather than face-down.
When the Right Side Is Better
People with heart failure are a notable exception to the left-side rule. The heart sits slightly left of center in the chest, and when you lie on your left side, the heart shifts closer to the chest wall. For a healthy heart this is insignificant, but for people whose heart doesn’t pump effectively, this position can worsen shortness of breath. Many heart failure patients instinctively prefer their right side for this reason. If you have a heart condition and notice discomfort or breathlessness on your left, switching to the right is a reasonable choice.
Side Sleeping During Pregnancy
The American College of Obstetricians and Gynecologists recommends side sleeping during the second and third trimesters. As the uterus grows, lying flat on your back can compress a major vein that returns blood to the heart, reducing blood flow to both you and the baby. Side sleeping avoids this compression. Left-side sleeping is often suggested because it keeps the uterus off the liver (which sits on the right) and may optimize blood flow to the placenta, but sleeping on either side is considered safe and far preferable to back sleeping in later pregnancy.
The Downsides of Side Sleeping
Side sleeping isn’t perfect. Two areas take the most wear: your shoulders and your skin.
When you sleep on your side, the bottom shoulder bears a significant portion of your body weight for hours at a time. Over months and years, this constant pressure can contribute to shoulder stiffness and pain, particularly if you already have a rotator cuff issue. The hip on the bottom side can develop similar soreness. If you tend to sleep on the same side every night, that shoulder and hip absorb a disproportionate amount of compression.
Your face also pays a price. The mechanical compression of pressing one side of your face into a pillow creates what dermatologists call sleep wrinkles. These typically appear on the forehead, cheeks, and lips, and unlike expression lines caused by muscle movement, they can’t be treated with Botox because they’re caused by physical pressure rather than muscle contraction. The only reliable prevention is sleeping on your back, which most side sleepers find difficult to maintain through the night.
How to Make Side Sleeping More Comfortable
A few simple changes can prevent the most common problems side sleepers run into.
- Place a pillow between your knees. This keeps your hips, pelvis, and spine aligned and prevents your top leg from falling forward and twisting your lower back. Without one, many side sleepers wake up with hip pain from that overnight rotation.
- Use a thicker pillow under your head. Side sleeping creates a wider gap between your head and the mattress than back sleeping does. A pillow that’s too thin lets your neck bend downward, straining muscles on one side. Your pillow should keep your head level with your spine.
- Hug a body pillow or place a pillow between your arms. This keeps your top shoulder from rolling forward and helps maintain a neutral position for the rotator cuff.
- Choose a medium-firm mattress. Too soft, and your shoulder and hip sink unevenly. Too firm, and pressure builds at those contact points. Medium-firm gives enough cushion for your shoulder while supporting your spine.
- Alternate sides. If you can train yourself to switch between left and right throughout the night, you’ll distribute pressure more evenly and reduce the risk of shoulder or hip pain developing on one side.
Left vs. Right: A Quick Comparison
- Acid reflux or heartburn: Left side keeps stomach acid below the esophageal opening.
- Heart failure: Right side reduces pressure on the heart and eases breathing.
- Pregnancy (second and third trimester): Either side works, with a slight preference for the left.
- General health with no specific conditions: Left side offers the most benefits for most people.
- Brain waste clearance: Either side is effective. Side sleeping in general outperforms stomach sleeping.
If you don’t have reflux, heart problems, or any condition that favors one side, the honest answer is that either side is fine. The difference between left and right is meaningful mainly for people with specific health concerns. What matters more for the average person is good alignment: the right pillow height, knee support, and a mattress that doesn’t create pressure points. Get those basics right, and whichever side you naturally gravitate toward will serve you well.