Side Sleeping Is Good for You. Just Get These 4 Things Right.

For most people, sleeping on your side is one of the best ways to sleep. Whether it leaves you rested or sore comes down to four things. Here's what the research says about each, and how to get them right.

Tonight you will change position about a dozen times without knowing it. When researchers in Denmark put small motion sensors on 664 adults and let them sleep at home, they counted an average of 1.6 position changes an hour. They also found where people spent the night: about 54% of it on their side, 38% on their back, and only 7% on their stomach.

So if you sleep on your side, you're doing what most human bodies choose on their own. And the research mostly backs that choice.

You breathe more easily. Your throat is a soft tube with no bones holding it open. On your back, gravity pulls your tongue and soft palate down into it, which is why snoring and sleep apnea get worse on the back. In a 2026 study of 338 adults with sleep apnea, breathing interruptions happened about 39 times an hour on the back and about 22 times an hour on the side.

It's the recommended position in pregnancy. Late in pregnancy, lying flat on the back lets the uterus press on the body's largest vein. The American College of Obstetricians and Gynecologists says side sleeping in the second and third trimesters "may be best."

What we don't know yet. You may have read that side sleeping helps the brain clear out waste at night. That idea comes from a 2015 study in anesthetized rats, not people. It's interesting, but it isn't proof.

Side sleeping does have a cost: you're resting a lot of weight on a small part of your body for hours. Four things decide whether that cost shows up as pain.

When you lie on your side, your shoulder lifts your body off the mattress. That leaves a gap between your ear and the bed, and your pillow has to fill it. Too thin, and your head drops toward the mattress. Too thick, and your head is pushed up. Either way, your neck stays bent all night.

The fix: choose a pillow that keeps your head level with your spine. Broad shoulders usually need a thicker pillow than narrow ones. If you wake with a stiff neck, your pillow height is the first thing to check.

On your side, much of your upper body rests on one shoulder and much of your lower body on one hip. On a firm mattress those two points can't sink in, so they take the load. That's why many side sleepers wake up with a sore shoulder or hip on the side they slept on.

The fix: a medium or medium-soft mattress, or a softer topper, lets your shoulder and hip settle in a little. Hugging a pillow also helps, because it keeps your top arm from dropping forward and rolling your shoulder in.

When you lie on your side, your top knee tends to slide forward and down toward the mattress. That rotates your pelvis and twists your lower back, and you hold that twist for hours. Curling into a tight ball causes a similar strain.

The fix: put a pillow between your knees so your top leg stays level with your hip. Keep a loose, gentle curve rather than a tight ball.

To be clear about the evidence: this advice comes from how the spine and pelvis are built and from what physical therapists recommend, not from large clinical trials. It's low-risk and easy to try, and if a knee pillow makes your back feel better in the morning, that's a good sign it's working for you.

Your stomach doesn't sit in the middle of your body. It hangs mostly to the left of your esophagus, the tube that carries food down from your mouth. On your left side, the stomach sits below the point where the two meet, so acid would have to flow uphill to get out. On your right side, that junction ends up lower, closer to the acid.

A 2023 review of the research found exactly this. Sleeping on the left side meant less acid in the esophagus than sleeping on the back or on the right side, and acid cleared faster. Right-side sleeping was no better than lying on your back. For snoring and sleep apnea, though, left and right work about equally well.

What about your heart? A common worry is that lying on your left side presses on the heart. Your heart does shift slightly inside your chest when you lie on your left, and that changes how a heart tracing (an ECG) looks. But in healthy people, there's no evidence that left-side sleeping harms the heart.

People with heart failure are different. In a study of 75 patients published in the Journal of the American College of Cardiology, many avoided their left side on their own during sleep, and those with larger hearts avoided it most. If you have a heart condition and the left side feels uncomfortable or makes you short of breath, trust that and talk to your doctor.

Another group should think about sides differently: people with glaucoma. In a study of glaucoma patients, eye pressure was higher in the lower eye when they lay on their side, about 19.1 compared with 17.6 mmHg. If you have glaucoma, ask your eye doctor which side, if any, to favor.

The fix: if you get heartburn at night, favor your left side. Otherwise, switch sides from night to night to spread the pressure around.

In 2016, plastic surgeons writing in the Aesthetic Surgery Journal described "sleep wrinkles": lines that can form when the face is pressed and pulled against a pillow night after night. They're more common in side and stomach sleepers, and more visible as skin ages.

The same authors admitted it's "extremely difficult" to change the position you sleep in, and there is no strong evidence yet that any pillow or pillowcase prevents these lines. We'd rather tell you that than sell you a promise.

1. Neck: a pillow that keeps your head level.
2. Shoulder and hip: a mattress soft enough to sink into a little.
3. Legs and lower back: a pillow between your knees.
4. Which side: the left if you get heartburn; otherwise, switch sides.

When to see a doctor first

See a doctor if you snore loudly, gasp at night or wake up exhausted; if you have a heart condition and lying on one side feels uncomfortable; if you have glaucoma or another eye condition; if you're pregnant and want advice for your situation; or if shoulder, hip or back pain doesn't improve after changing your pillow or mattress.

Is it bad to sleep on your side every night?

No. For most healthy adults it's fine and often helpful, as long as your pillow and mattress keep your spine in a straight line.

Which side is better, left or right?

For heartburn and acid reflux, the left side. For snoring and sleep apnea, studies find little difference between the two.

Is sleeping on your left side bad for your heart?

For healthy people, there's no evidence that it is. The heart shifts slightly when you lie on your left, which changes an ECG reading, but that isn't damage. People with heart failure often find the left side uncomfortable and avoid it naturally. If that's you, follow your comfort and your doctor's advice.

Can side sleeping damage your spine?

There's no good evidence that the position itself damages the spine. Pain usually comes from a pillow of the wrong height, a mattress that's too firm, or a top leg that twists the lower back.

Does side sleeping cause wrinkles?

It can contribute to "sleep wrinkles" over many years. How much varies a lot from person to person.

What's the worst sleep position for your neck?

Stomach sleeping, because you have to keep your head turned to one side all night to breathe.

About us: we make sleep products for side sleepers, including a wraparound sleep mask designed to stay on when you turn over. That's why we wanted to get this article right. No product we sell matters as much as the four things above.

This article is for general information and is not medical advice. If you have a health condition or ongoing pain, talk to a qualified healthcare professional.

Sources

1. Skarpsno ES, et al. Sleep positions and nocturnal body movements based on free-living accelerometer recordings. Nature and Science of Sleep, 2017.
2. The effect of different sleep positions on the severity of obstructive sleep apnea: a retrospective study. Nature and Science of Sleep, 2026.
3. Left lateral decubitus sleeping position is associated with improved gastroesophageal reflux disease symptoms: a systematic review and meta-analysis. 2023.
4. American College of Obstetricians and Gynecologists. Can I sleep on my back when I'm pregnant?
5. Lee H, et al. The effect of body posture on brain glymphatic transport. Journal of Neuroscience, 2015.
6. Anson G, et al. Sleep wrinkles: facial aging and facial distortion during sleep. Aesthetic Surgery Journal, 2016.
7. Effect of lateral decubitus position on intraocular pressure in glaucoma patients with asymmetric visual field loss. Ophthalmology, 2013.
8. Leung RS, et al. Avoidance of the left lateral decubitus position during sleep in patients with heart failure: relationship to cardiac size and function. Journal of the American College of Cardiology, 2003.
9. Body position effects on the ECG: implication for ischemia monitoring. Journal of Electrocardiology, 1997.