For most people, the left side is the best side to sleep on. Left-side sleeping keeps acid reflux at bay, aids digestion, and may even help your brain clear waste more efficiently during the night. But the ideal side depends on your specific health situation, and in some cases, the right side is actually the better choice.
Left Side for Acid Reflux
If you deal with heartburn or GERD, sleeping on your left side is one of the simplest things you can do to reduce nighttime symptoms. Up to 80% of people with GERD experience symptoms at night, and sleep position plays a direct role in how severe those episodes get.
The reason is anatomy. When you lie on your left side, the junction between your esophagus and stomach sits higher than the stomach itself. Gravity helps keep stomach acid where it belongs, and any acid that does splash up drains back down more quickly. Lying on the right side reverses this arrangement, making it easier for acid to pool in the esophagus. Research confirms that left-side sleeping reduces nighttime reflux more effectively than sleeping on your back or right side.
Left Side for Digestion
Your digestive tract isn’t symmetrical. The small intestine empties waste into the large intestine through a valve in your lower right abdomen. From there, waste travels up the ascending colon (on your right), across the transverse colon, and down the descending colon (on your left) toward the rectum. When you sleep on your left side, gravity assists this entire route, encouraging waste to move naturally through each section. That’s one reason left-side sleepers often find it easier to have a bowel movement in the morning.
Right Side for Heart Failure
Left-side sleeping isn’t ideal for everyone. People with heart failure often experience worsening shortness of breath when lying on the left side, because the heart shifts slightly and presses against the chest wall under gravity. Many heart failure patients find the right side more comfortable and less likely to trigger breathlessness during the night. If you have a heart condition and notice discomfort on one side, the right side is worth trying.
Either Side for Snoring and Sleep Apnea
Sleeping on your back is the worst position for snoring and obstructive sleep apnea. When you’re face-up, gravity pulls the tongue and soft tissues backward, narrowing or blocking the airway. Rolling onto either side opens the airway and can dramatically reduce breathing interruptions.
The improvement varies from person to person. In one case documented by the American Thoracic Society, a patient’s breathing events dropped from 87 per hour on the right side to 17 per hour on the left, illustrating that even the choice between left and right can matter for some individuals. If you’ve been diagnosed with positional sleep apnea, a sleep study will show which position works best for you specifically.
Brain Waste Clearance During Side Sleep
Your brain has its own waste-removal system that kicks into high gear while you sleep. It flushes out metabolic byproducts, including proteins linked to Alzheimer’s disease, by circulating cerebrospinal fluid through brain tissue. A study published in The Journal of Neuroscience found that this cleaning process was most efficient in the lateral (side-lying) position compared to sleeping on the back or stomach. In animals sleeping on their stomachs with their heads more upright, waste clearance slowed and fluid was retained rather than flushed out. Both left and right side positions outperformed stomach sleeping, though the lateral position overall showed the strongest results.
The Downside: Shoulder and Skin Pressure
Side sleeping does come with trade-offs. The shoulder bearing your weight all night can develop problems over time. Prolonged pressure squeezes the rotator cuff tendons between two bones in the shoulder, a process called impingement. Over months and years, this repeated compression can progress from mild irritation to inflamed bursae (the small cushioning sacs in the joint), tendon damage, and even full rotator cuff tears. The shoulder’s cartilage can also break down, leading to osteoarthritis. If you wake up with shoulder pain, alternating sides or placing a supportive pillow under your arm can reduce the load on the joint.
Your face takes a hit too. A study in the Aesthetic Surgery Journal found that compression, tension, and shear forces from pressing your face into a pillow cause sleep wrinkles that worsen over time. Unlike expression lines caused by muscle movement, sleep wrinkles form from mechanical pressure and can’t be treated with Botox. As skin thins and loses elasticity with age, these creases become permanent. People who sleep on the same side every night often notice deeper lines on that side of the face.
How to Set Up for Side Sleeping
Pillow choice matters more for side sleepers than any other position. You need a thicker pillow than back sleepers to fill the gap between your ear and the mattress and keep your neck aligned with your spine. A pillow that works well on your back will almost certainly be too low for side sleeping, leaving your head tilted downward and straining your neck.
The second critical adjustment is between your knees. Without support, your top leg drops forward and pulls your pelvis out of alignment, twisting the spine. A firm pillow between the knees prevents this rotation and keeps your hips, pelvis, and lower back in a neutral line. A soft pillow tends to compress too much to hold your legs apart effectively.
If you’re trying to switch from back sleeping to side sleeping, placing a body pillow behind you can prevent you from rolling over during the night. For people managing reflux, elevating the head of the bed by a few inches in addition to sleeping on the left side provides even more protection against acid creeping up the esophagus.