For most people, sleeping on the left side offers the widest range of health benefits. It helps with digestion, keeps airways more open, and during pregnancy is the recommended position for blood flow to the baby. That said, the best side depends on your specific health situation, and in some cases, the right side is actually the better choice.
Left Side for Digestion and Acid Reflux
If you deal with heartburn or acid reflux, the left side is your best bet. The anatomy here is straightforward: your stomach sits slightly to the left of your body, and when you lie on your left side, the opening where your esophagus meets your stomach sits higher than the stomach itself. Gravity helps keep acid down in the stomach rather than letting it creep back up into the esophagus. Roll onto your right side, and that geometry flips. The stomach opening sits lower, making it much easier for acid to escape upward.
This is especially relevant after eating. If you lie down within a couple of hours of a meal, left-side sleeping can make a noticeable difference in whether you wake up with that burning sensation in your chest or throat.
Why Pregnant Women Are Told to Sleep on the Left
During pregnancy, left-side sleeping is the standard recommendation. A large vein called the inferior vena cava runs along the right side of your spine, carrying blood from your lower body back to your heart. As the uterus grows, sleeping on your back puts the full weight of the baby and uterus directly on that vein, reducing blood return to your heart and decreasing blood flow to the placenta.
Sleeping on the left side relieves that pressure. It allows the most blood to flow to the baby and also improves kidney function, which helps reduce swelling in the feet and ankles. Lying on the back can also cause lower back pain and intestinal discomfort from the added pressure. If you find yourself waking up on your back, don’t panic. Simply roll to your left side and settle back in. The occasional shift is normal and not dangerous.
Brain Waste Clearance During 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 neurological decline, by circulating fluid through brain tissue. Research published in the Journal of Neuroscience found that this cleaning system works most efficiently when sleeping on your side compared to sleeping on your back or stomach. Stomach sleeping performed the worst, with slower clearance and more fluid retention in the brain.
The study was conducted in animals, so the exact numbers don’t translate directly to humans. But the finding aligns with the fact that side sleeping is by far the most common position. Roughly 65% of people sleep on their side naturally, suggesting it may be the position our bodies are built to favor.
Sleep Apnea and Snoring
If you snore or have obstructive sleep apnea, side sleeping on either side is significantly better than sleeping on your back. When you lie face-up, gravity pulls the tongue and soft tissues of the throat backward, narrowing or blocking the airway. This is why snoring tends to be loudest in the supine position.
Switching from back sleeping to side sleeping reduces the frequency of breathing interruptions by about 54%, according to a meta-analysis of positional therapy studies. It also improves blood oxygen levels during the night. For people with position-dependent sleep apnea (meaning their episodes are mostly or entirely triggered by back sleeping), simply staying on their side can be as effective as other interventions. Tennis balls sewn into the back of a sleep shirt, wedge pillows, and wearable vibrating devices are all commonly used to keep people off their backs.
When the Right Side May Be Better
Left-side sleeping isn’t ideal for everyone. Some people with heart conditions find that sleeping on the left side feels uncomfortable because gravity shifts the heart slightly within the chest. This repositioning is measurable on imaging, and while it’s generally harmless, it can create a sensation of pressure or an awareness of your heartbeat that makes it harder to fall asleep. If you have heart failure or another cardiac condition and notice discomfort on the left side, the right side may feel better and still gives you the airway and digestive benefits of lateral sleeping.
People with hip bursitis or shoulder pain also need to consider which side they sleep on carefully. Lying directly on an inflamed hip joint or a sore shoulder compresses the tissues and can worsen pain overnight. If your left hip or shoulder is the problem, sleeping on the right side (or vice versa) is the practical answer. Placing a pillow between your knees helps keep the hips aligned and reduces strain on the lower back regardless of which side you choose.
The Downside of Side Sleeping for Skin
One trade-off of side sleeping is its effect on your face over time. Pressing your cheek, forehead, and lips into a pillow every night creates mechanical compression that gradually forms wrinkles. These “sleep wrinkles” are distinct from expression lines. They tend to run perpendicular to the wrinkles caused by smiling or squinting, and they show up most on the forehead, cheeks, and around the lips.
Because these wrinkles come from physical pressure rather than muscle movement, treatments like Botox don’t help with them. Dermal fillers can temporarily smooth them out, but the only real prevention is reducing the compression itself. Silk or satin pillowcases create less friction, and specially contoured pillows can reduce how much your face presses into the surface. Back sleeping avoids the problem entirely, but as dermatologists acknowledge, consciously changing your sleep position is extremely difficult.
How to Make Side Sleeping More Comfortable
Your pillow height matters more than most people realize. A side sleeper needs a thicker pillow than a back sleeper because the gap between your head and the mattress is wider. The goal is to keep your spine in a straight line from your neck through your lower back. If your pillow is too thin, your head droops toward the mattress and strains one side of your neck. Too thick, and it pushes your head upward.
A knee pillow prevents your top leg from pulling your pelvis forward, which is a common cause of lower back and hip pain in side sleepers. Your mattress also plays a role: side sleeping concentrates your weight on the shoulder and hip, so a medium or medium-soft mattress that lets those pressure points sink in slightly tends to work better than a very firm surface. If you wake up with numbness in the arm you’re sleeping on, try hugging a pillow to keep your bottom arm slightly forward rather than tucked directly under your body.