Sleeping on your left side is the best position for most people. It reduces acid reflux, supports healthy blood flow, and keeps pressure off internal organs. That said, the ideal position can shift depending on your specific health concerns, and side sleeping in general offers advantages over sleeping on your back or stomach.
Why the Left Side Wins for Most People
The left side gets the strongest recommendation because of simple anatomy. When you lie on your left, your stomach sits below your esophagus, so gravity helps keep stomach acid where it belongs. When you lie on your right, this relationship flips: your stomach ends up above the junction where it meets the esophagus, making it easier for acid to flow upward and cause heartburn. A systematic review and meta-analysis found that left-side sleeping significantly reduced both acid exposure time and acid clearance time compared to right-side and back sleeping.
Beyond digestion, left-side sleeping promotes better circulation. Dr. Virend Somers, a cardiologist and director of the sleep facility within Mayo Clinic’s Center for Clinical and Translational Science, notes that sleeping on the left side “keeps pressure off internal organs and promotes healthy blood flow.” Your heart sits slightly left of center in your chest, and this position allows blood to flow more efficiently through your largest blood vessel (the aorta) as it curves leftward from the heart.
Left Side Sleeping During Pregnancy
The recommendation becomes especially important in the third trimester of pregnancy. When a pregnant person lies flat on their back, the weight of the uterus compresses the large vein that returns blood from the lower body to the heart. This compression can lower blood pressure and reduce blood flow to the baby. The effect is well-established enough that clinicians routinely avoid placing pregnant patients on their backs during examinations and procedures, and will reposition a laboring mother to her left side at the first sign of fetal distress.
If you’re in your third trimester, making a habit of falling asleep on your left side is one of the simplest things you can do for both your own comfort and your baby’s oxygen supply.
Side Sleeping and Snoring
If snoring or sleep apnea is your main concern, either side is better than your back. Lying face-up allows gravity to pull the tongue and soft tissues of the throat backward, partially blocking the airway. The difference can be dramatic. In one clinical case documented by the American Thoracic Society, a patient’s breathing disruptions dropped from 87 events per hour while on one side to just 6 events per hour in another position, illustrating how profoundly body position can affect airway obstruction.
For people with positional sleep apnea, where symptoms are significantly worse on the back, simply switching to side sleeping can sometimes reduce the severity from a level that requires treatment to one that doesn’t. If your partner tells you that you snore loudly when you’re on your back but quietly when you roll over, position is likely a major factor.
Brain Waste Clearance During Sleep
Your brain has its own waste-removal system that becomes most active during sleep. This system flushes out harmful byproducts, including the proteins associated with Alzheimer’s disease. Research has identified sleep position as one of several lifestyle factors that influence how efficiently this cleanup process works, alongside exercise, diet, and sleep quality. Side sleeping appears to support this drainage, though the bulk of the evidence confirms that getting deep, uninterrupted sleep matters more than any single position.
When Right-Side Sleeping Makes Sense
The right side isn’t always the wrong choice. People with certain heart conditions sometimes find the left side uncomfortable because the heart shifts closer to the chest wall in that position, creating a sensation of pressure or a more noticeable heartbeat. If lying on your left side makes you feel your heart pounding, the right side is a reasonable alternative. For people without acid reflux or pregnancy concerns, right-side sleeping is perfectly fine and still offers the airway benefits of any lateral position over back sleeping.
The Tradeoffs of Side Sleeping
Side sleeping does come with a couple of downsides worth knowing about. The first is shoulder pressure. A study of 83 patients with one-sided shoulder pain found that 67% of those who slept on one side were sleeping on their painful shoulder. Whether the position caused the pain or people simply gravitated toward that side isn’t fully settled, but if you have shoulder trouble, try sleeping on the opposite side or switching sides of the bed so you naturally face away from your partner on your pain-free shoulder.
The second tradeoff is skin aging. Pressing one side of your face into a pillow for hours every night creates compression lines, particularly along the jawline, cheek, and around the eyes. Over years, these temporary creases can become permanent as the repeated folding breaks down collagen in those spots. If this concerns you, alternating sides, using a silk pillowcase, or trying a pillow designed to reduce facial contact can help. Sleeping on your back eliminates compression wrinkles entirely, but for most people the circulatory and digestive benefits of side sleeping outweigh the cosmetic tradeoff.
How to Set Up for Comfortable Side Sleeping
Position alone isn’t enough. Poor alignment while side sleeping can leave you with back pain or a stiff neck. The Mayo Clinic recommends drawing your legs up slightly toward your chest and placing a pillow between your knees. This keeps your spine, pelvis, and hips aligned and takes pressure off your lower back. A full-length body pillow works well if you tend to shift positions throughout the night.
Your head pillow matters too. It should be thick enough to fill the gap between your ear and the mattress so your neck stays straight rather than bending up or down. A pillow that’s too thin lets your head drop toward the mattress, straining the neck. One that’s too thick pushes your head upward, creating the same problem in the opposite direction. The right thickness depends on your shoulder width: broader shoulders need a thicker pillow.
If you’re not naturally a side sleeper, placing a pillow or rolled towel behind your back can keep you from rolling over during the night. Some people also find that a slightly firmer mattress makes side sleeping more comfortable, since a very soft surface lets the hips sink too far and throws the spine out of alignment.