Side sleeping, particularly on your left side, is the best position for most people. It keeps your airways open, supports digestion, and may even help your brain clear waste more efficiently. That said, the ideal position depends on your body and any conditions you’re managing. Adults already spend about 54% of their sleep time on their side, 38% on their back, and just 7% on their stomach.
Why Side Sleeping Works for Most People
Side sleeping hits the most health benefits with the fewest tradeoffs. It naturally keeps your airway open, which reduces snoring and can ease mild sleep apnea. It’s also the most common position humans gravitate toward, and there may be a biological reason for that.
A study published in the Journal of Neuroscience found that the brain’s waste-clearance system works most efficiently in the lateral (side) position. This system flushes out metabolic byproducts during sleep, including amyloid-beta, a protein linked to Alzheimer’s disease. In the study, both side and back positions outperformed stomach sleeping, but the lateral position showed the strongest results. The researchers proposed that the popularity of side sleeping across species may have evolved specifically to optimize this cleanup process.
The left side has a slight edge over the right for one key reason: acid reflux. When you lie on your left side, your stomach sits below your esophagus, making it harder for stomach acid to travel upward. Sleeping on the right side can worsen heartburn symptoms. If you deal with reflux regularly, training yourself to favor the left side can make a noticeable difference.
When Back Sleeping Is the Better Choice
Back sleeping is a strong option if you have low-back pain. Many people find that lying face-up helps relieve pressure on the lumbar spine, especially with a pillow under the knees to maintain the natural curve of the lower back. It’s also the best position for your skin. Because your face isn’t pressed into a pillow, you avoid the repeated compression that can cause creases, breakouts, and over time, permanent changes to the skin.
Back sleeping has two notable downsides. It tends to worsen snoring and sleep apnea because gravity pulls the tongue and soft tissues toward the back of the throat, partially blocking the airway. And if you have neck pain, lying face-up can sometimes make it worse rather than better. For people without these issues, though, back sleeping is a perfectly good option.
Why Stomach Sleeping Is the Hardest on Your Body
Stomach sleeping is the least recommended position. To breathe, you have to turn your head sharply to one side, which twists the cervical spine for hours at a time. That sustained rotation puts constant tension on the neck muscles and upper back. Meanwhile, your lower back sinks into the mattress while your hips stay extended, compressing the lumbar spine and tightening the muscles around it.
The one genuine benefit of stomach sleeping is that, like side sleeping, it keeps the airway more open than lying on your back. If you’re a stomach sleeper who can’t switch, placing a pillow under your hips and lower abdomen can reduce the strain on your lower back. You can also try sleeping without a head pillow, or with a very thin one, to limit how much your neck has to twist.
Adjustments for Specific Conditions
Heart Failure
People with heart failure often feel more short of breath when sleeping on the left side, because of how the heart sits in the chest relative to the lungs and surrounding structures. Many naturally shift to the right side for comfort. If you have heart failure, the right side is generally the more comfortable choice.
Pregnancy
After 28 weeks of pregnancy, back sleeping increases the risk of stillbirth. Six separate research trials have confirmed this link. The reason is mechanical: the weight of the baby and uterus compresses the main blood vessels that supply the placenta, restricting blood flow and oxygen. Side sleeping is the safer choice in the third trimester. While many sources recommend the left side specifically, the evidence hasn’t conclusively shown that left is safer than right. Either side is a significant improvement over back sleeping at that stage.
Back and Neck Pain
Pillow placement matters as much as position. If you sleep on your side, drawing your knees up slightly and placing a pillow between your legs helps align your spine, pelvis, and hips. A full-length body pillow works well for this. If you sleep on your back, a pillow under your knees relaxes the lower back muscles. A small rolled towel under your waist can add extra support. In either position, your head pillow should keep your neck aligned with your chest and back, not propped up at an angle.
How to Change Your Sleep Position
Most people shift positions throughout the night without realizing it, so you don’t need to stay locked in one pose for eight hours. The goal is to start in the position you’re aiming for and set up your pillows to encourage staying there. If you’re trying to stop sleeping on your back, some people use the “tennis ball trick,” placing a tennis ball in a pocket sewn onto the back of a sleep shirt to make rolling over uncomfortable.
Switching from stomach sleeping to side sleeping is the most common transition. A body pillow can help by giving you something to wrap around, which mimics the “hugging the mattress” feeling that stomach sleepers are used to. Most people adjust within a few weeks. Your body naturally favors the position where it gets the best sleep, so once you reduce the discomfort your old position was causing, the new one tends to stick.