For most people, the left side is the better side to sleep on. It reduces acid reflux, supports digestion, and keeps a major vein free from compression. That said, the “best” side depends on your body and health conditions. People with heart failure, for example, often do better on their right side. Adults already spend about 54% of their sleep time on their side, so the real question is which side and what trade-offs come with it.
Why Left-Side Sleeping Has the Edge
The left side gets the most universal recommendation, and the reason is anatomy. When you lie on your left, your esophagus and the muscular ring at its base sit higher than your stomach. Gravity helps acid drain back down rather than creeping up into your throat. If you deal with heartburn or gastroesophageal reflux, this single change can noticeably reduce nighttime symptoms.
Your stomach also empties more efficiently on the left side. The stomach’s natural curve means food and digestive juices flow toward the lower outlet (the pylorus) when you’re oriented this way, rather than pooling near the esophageal opening. People who eat late or have slow digestion often notice a difference.
Left Side During Pregnancy
Healthcare providers worldwide recommend left-side sleeping during pregnancy, particularly in the second and third trimesters. The reason centers on a large vein called the inferior vena cava, which runs along the right side of your spine and carries blood back to your heart. As the uterus grows, it can press directly on this vein when you lie on your back or right side, reducing blood flow.
Sleeping on your left prevents that compression. The result is better blood return to your heart, enhanced blood flow through the placenta, and more oxygen and nutrients reaching the baby. If you wake up on your back or right side, there’s no need to panic. Simply roll to your left and settle back in. A pillow between your knees can help you stay in position.
When the Right Side Is Better
People with heart failure often find that sleeping on their left side worsens shortness of breath. The heart sits slightly left of center in the chest, and lying on that side shifts its weight and changes how blood fills the chambers. Many heart failure patients naturally gravitate to their right side for comfort and easier breathing.
If you have no cardiac issues, right-side sleeping is still a perfectly fine option. It carries the same general benefits of lateral sleeping (reduced snoring, open airways) without the specific digestive advantages of the left side. For people with left shoulder pain or injuries, switching to the right can relieve pressure while still keeping you off your back.
Side Sleeping and Snoring
Regardless of which side you choose, sleeping laterally is one of the most effective ways to reduce snoring and manage obstructive sleep apnea. When you sleep on your back, gravity pulls the tongue and soft tissues backward, partially blocking the airway. Rolling to either side keeps the airway more open.
Research on positional therapy for sleep apnea has shown that the number of breathing interruptions per hour can more than double in the back position compared to side sleeping. For people with mild to moderate sleep apnea, simply staying off the back sometimes reduces symptoms enough to avoid other interventions. Tennis balls sewn into the back of a sleep shirt or wedge-style positional pillows are low-tech ways to train yourself to stay on your side.
Brain Waste Clearance During Sleep
Your brain has a waste-removal system that ramps up during sleep, flushing out proteins like amyloid-beta and tau that accumulate during waking hours. These are the same proteins linked to Alzheimer’s disease. Research published in Frontiers in Neurology has found that lateral sleeping positions are more efficient at driving this clearance process than sleeping on your back or stomach.
The mechanism relies on cerebrospinal fluid circulating through channels around blood vessels in the brain. Side sleeping appears to optimize this flow. Sleep deprivation impairs the process regardless of position, so getting enough total sleep still matters more than which side you pick.
The Downsides of Side Sleeping
Side sleeping concentrates your body weight through a relatively small area: your shoulder, hip, and the side of your ribcage. Over time, this sustained pressure can irritate the shoulder joint. The most common result is bursitis, where the fluid-filled cushion inside the joint becomes inflamed and swollen. If you already have a rotator cuff issue or shoulder impingement, sleeping on that side will likely make it worse.
Alternating sides during the night helps distribute the load. A mattress with enough give to let your shoulder and hip sink slightly, rather than bearing all the force, also reduces the risk. Placing a pillow between your knees keeps your spine aligned and takes strain off your lower back and hips.
Wrinkles and Skin
Side sleeping presses one half of your face into the pillow for hours at a time. This mechanical compression creates “sleep wrinkles” that are distinct from expression lines. They tend to appear on the forehead, cheeks, and lips, often running perpendicular to the wrinkles caused by smiling or squinting. A study highlighted by The Aesthetic Society noted that these compression wrinkles can’t be treated with Botox because they aren’t caused by muscle contractions. Dermal fillers can temporarily smooth them, but the only real prevention is sleeping on your back or using a specialty pillow designed to keep your face off the surface.
Changing a lifelong sleep position is genuinely difficult. Most people shift positions dozens of times per night without waking. If skin aging is a concern but you can’t tolerate back sleeping, a silk or satin pillowcase reduces friction and may slow the process somewhat.
How to Choose Your Side
If you have acid reflux, digestive issues, or are pregnant, default to your left. If you have heart failure or left-shoulder pain, the right side is the smarter choice. If none of those apply, either side works well, and both outperform back sleeping for airway health and brain waste clearance.
The position you fall asleep in isn’t necessarily the one you stay in. Most people rotate between sides and occasionally shift to their back throughout the night. Rather than obsessing over perfect positioning, focus on the conditions that help you stay lateral: a supportive pillow that fills the gap between your ear and shoulder, a mattress that cushions pressure points, and a body pillow or knee pillow if you tend to roll onto your back. The best sleep position is ultimately one that lets you sleep deeply and wake without pain.