For most people, the left side is the better side to sleep on. It improves digestion, reduces acid reflux, and supports your brain’s natural waste-clearing process during sleep. That said, certain health conditions can flip the recommendation, so the best side for you depends on what your body needs most.
Why Left-Side Sleeping Gets the Top Recommendation
The left side wins for most sleepers because of how your organs are arranged. Your stomach naturally curves to the left, so when you lie on that side, gravity keeps stomach acid pooled away from the opening to your esophagus. The American Gastroenterological Association specifically recommends left-side sleeping for people with nighttime acid reflux because this position reduces how much acid creeps upward.
Even if you don’t have reflux, left-side sleeping supports digestion more broadly. Food moves from your stomach into your small intestine through an opening on the right side of the stomach. When you lie on your left, gravity helps guide that process along its natural path rather than working against it.
Left-Side Sleeping During Pregnancy
If you’re pregnant, especially in the second and third trimesters, sleeping on your left side is considered the gold standard. A large vein called the inferior vena cava runs along the right side of your spine, carrying blood back to your heart from your lower body. As the uterus grows, sleeping on your back or right side can press against this vein, reducing blood flow.
Lying on your left keeps the uterus off that vein, which maximizes blood flow to the placenta. That means more oxygen and nutrients reaching your baby. Healthcare providers worldwide recommend this position for pregnant sleepers, and it can also help reduce swelling in your legs and feet by improving overall circulation.
When Right-Side Sleeping Is Better
People with heart failure often find that sleeping on the left side makes breathing harder. The heart sits slightly to the left in the chest, and lying on that side can create a sensation of pressure or increased shortness of breath. Many people with heart failure naturally gravitate toward sleeping on their right side for this reason. If you have a heart condition and notice discomfort on your left, switching to your right is a reasonable choice.
Side Sleeping and Brain Health
Your brain has its own cleaning system that ramps up during sleep, flushing out metabolic waste products, including proteins linked to Alzheimer’s disease. Research published in the Journal of Neuroscience found that this cleaning process works most efficiently when sleeping on your side compared to sleeping on your back or stomach. The researchers noted that side sleeping is already the most common position across species, and they proposed it may have evolved specifically to optimize this waste removal. The study didn’t find a significant difference between left and right side for this effect, so either side appears to offer the brain-clearing benefit.
Side Sleeping Reduces Snoring and Sleep Apnea
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, partially blocking your airway. In people with positional sleep apnea, the number of breathing disruptions per hour is at least twice as high when sleeping on the back compared to sleeping on either side. Positional therapy, which simply means training yourself to stay off your back, is one of the most straightforward interventions for mild to moderate cases.
How to Set Up Your Pillows
Side sleeping puts more distance between your head and the mattress than back sleeping does, because your shoulder takes up space. A pillow that’s too thin lets your head tilt downward, straining your neck. A pillow that’s too thick pushes it upward. You want one that fills the gap evenly so your head, neck, and spine form a straight line.
The second pillow matters just as much. Place a small pillow or a rolled-up towel between your knees. Without it, your top leg drops across your body, pulling your hips out of alignment and putting pressure on your lower back. This simple adjustment can make a noticeable difference if you wake up with hip or lower back stiffness. If you deal with shoulder pain, look for a pillow firm enough to keep weight distributed rather than letting your shoulder compress into the mattress.
The Trade-Off: Skin and Wrinkles
There is one downside to side sleeping that’s worth knowing about. Pressing your face against a pillow for hours creates mechanical compression on your skin. Over time, this contributes to sleep wrinkles, particularly on the forehead, cheeks, and around the lips. These wrinkles form differently from expression lines. They’re caused by physical pressure, not muscle movement, which means treatments like Botox don’t help with them.
About 65% of people sleep on their side, so this affects most of us. The wrinkles tend to get more noticeable with age as skin loses elasticity and becomes thinner. Silk or satin pillowcases create less friction than cotton, and some specially shaped pillows are designed to reduce facial contact. That said, consciously changing your sleep position is notoriously difficult, and for most people, the cardiovascular, digestive, and neurological benefits of side sleeping outweigh the cosmetic concerns.
Choosing Your Best Side
If you’re generally healthy, go with the left side. You’ll get the digestive benefits, the acid reflux protection, and the same brain-clearing advantages as the right side. If you’re pregnant, left is especially important for blood flow to your baby. If you have heart failure or a cardiac condition that makes left-side sleeping uncomfortable, the right side is a better fit. And if you snore or have sleep apnea, either side beats sleeping on your back.
Most people shift positions multiple times during the night, and that’s completely normal. Starting on your preferred side and using pillows to support your alignment gives your body the best chance of staying comfortable in that position longer.