For most people, the left side is the best side to sleep on. It offers the strongest combination of digestive, circulatory, and respiratory benefits. But the ideal position can shift depending on your health, particularly if you’re pregnant, managing heart failure, or dealing with acid reflux.
Why the Left Side Wins for Most People
Your internal organs aren’t symmetrical, and that’s why sleep position matters. Your stomach sits slightly to the left of your midline, and the junction where your esophagus connects to your stomach enters from the right side. When you sleep on your left, gravity keeps stomach acid pooled away from that opening, which means less chance of acid creeping upward into your throat.
A study of 57 people with chronic heartburn found that acid reflux episodes happened at roughly the same rate regardless of position. The key difference was how quickly the acid cleared: it resolved much faster when participants slept on their left side compared to their right side or back. So left-side sleeping doesn’t necessarily prevent reflux from happening, but it shortens each episode and reduces the burn.
Left-side sleeping also supports your lymphatic system and may help your body filter waste more efficiently during sleep. Your largest lymphatic vessel drains on the left side of your body, and sleeping in that position lets gravity assist the process rather than work against it.
Left-Side Sleeping During Pregnancy
Side sleeping becomes more than a preference during pregnancy. It’s a clinical recommendation. As the uterus grows, lying flat on your back puts the full weight of the baby, uterus, and amniotic fluid directly on the inferior vena cava, the large vein responsible for returning blood from your lower body to your heart. That compression can reduce blood flow to both you and the baby, potentially causing dizziness, low blood pressure, and decreased oxygen delivery to the placenta.
The left side is especially recommended because it maximizes blood flow to the baby. While sleeping on the right side is still far better than sleeping on your back, the left side avoids any pressure on that major vein entirely. If staying on your left side all night feels impossible, placing a pillow between your knees and another under your belly can create enough of a tilt to keep you comfortable. Many people naturally shift positions during sleep, and that’s fine. The goal is to start on your left and make it your default.
When the Right Side Is Better
There’s one notable exception to the left-side rule: heart failure. People with heart failure often experience worsening shortness of breath when they sleep on their left side, according to the American Heart Association. The reason is mechanical. Lying on your left puts your heart closer to the chest wall and can increase the sensation of pressure or labored breathing. Many heart failure patients instinctively prefer the right side, and that preference aligns with better comfort and sleep quality for them.
If you have a healthy heart, this doesn’t apply to you. The slight additional pressure of left-side sleeping on a normally functioning heart is negligible and causes no harm. But for anyone already managing reduced cardiac function, the right side can make a meaningful difference in how well you breathe overnight.
How Side Sleeping Affects Your Skin
One downside of side sleeping, regardless of which side, is its effect on your face over time. Research published in the Aesthetic Surgery Journal found that sleeping on your side or stomach creates compression, tension, and shear forces on facial skin. These forces distort the skin night after night, eventually forming “sleep wrinkles” that deepen with age as skin thins and loses elasticity.
Sleep wrinkles are distinct from expression lines. Expression lines form from repeated muscle contractions (smiling, squinting), while sleep wrinkles come purely from mechanical pressure. This distinction matters because treatments like Botox, which relax muscles, won’t improve sleep wrinkles at all. Dermal fillers can temporarily soften them, and treatments that promote collagen production may help reduce their appearance over time.
If you’re concerned about facial aging, sleeping on your back eliminates the problem entirely. Specialty pillows designed to cradle the head without pressing on the face can help side sleepers reduce contact. Realistically, though, most people won’t switch to back sleeping for cosmetic reasons alone. Using sunscreen, maintaining good skin care, and not smoking will do more for skin aging than any sleep position change.
Making Side Sleeping More Comfortable
Switching to side sleeping, or switching sides, takes some adjustment. Your pillow height matters more than you might think. A pillow that’s too flat lets your head drop toward the mattress, bending your neck sideways. One that’s too thick pushes your head upward. Either way, you end up with neck pain. The right pillow fills the gap between your ear and the outside of your shoulder, keeping your spine in a straight line.
A pillow between your knees prevents your top leg from pulling your hips out of alignment, which is a common source of lower back and hip pain for side sleepers. If you tend to roll onto your back during the night, placing a body pillow behind you can act as a gentle barrier.
People who’ve slept on one side for years sometimes notice shoulder pain on that side. Alternating between left and right throughout the night distributes the pressure more evenly. If you’re prioritizing the left side for digestive or pregnancy reasons, a mattress with good pressure relief at the shoulder can help you stay there longer without discomfort.
Quick Comparison by Health Goal
- Acid reflux or heartburn: Left side. Acid clears faster and sits further from the esophageal opening.
- Pregnancy (especially third trimester): Left side. Maximizes blood flow to the baby and avoids compressing the vena cava.
- Heart failure: Right side. Reduces shortness of breath and chest pressure during sleep.
- Snoring or mild sleep apnea: Either side. Side sleeping keeps the tongue and soft palate from collapsing into the airway, which is the main cause of snoring on your back.
- Wrinkle prevention: Back sleeping is ideal. If you must sleep on your side, specialty pillows can reduce facial compression.
- General health with no specific conditions: Left side is the safest default.