Side sleeping is not bad for you. It’s the most common sleep position, used by more than 60% of adults, and it offers several measurable health benefits. That said, side sleeping can cause problems for your shoulders, hips, and skin if your setup isn’t right. The position itself is sound; the details of how you do it matter.
Benefits of Side Sleeping
Side sleeping has real advantages that go beyond comfort. For people who snore or have obstructive sleep apnea, switching from back sleeping to side sleeping can cut the number of breathing interruptions per hour by more than 50%, according to a meta-analysis of positional therapy studies. When you sleep on your back, gravity pulls your tongue and soft tissue toward the back of your throat, partially blocking your airway. Sleeping on your side keeps that airway open.
If you deal with acid reflux, your left side is the better choice. When you lie on your left side, your stomach sits below your esophagus, making it harder for acid to travel upward. Harvard Health reports that acid clears much faster in the left-side position compared to sleeping on your back or right side. Less acid exposure means less pain and less risk of damage to the tissue lining your esophagus.
There’s also evidence that side sleeping helps your brain clean house. A 2015 study published in the Journal of Neuroscience found that the brain’s waste-clearance system, which flushes out harmful proteins during sleep, works most efficiently in the lateral (side) position compared to sleeping on your back or stomach. The researchers specifically tracked clearance of beta-amyloid, a protein linked to Alzheimer’s disease, and found it was removed faster when subjects were on their side.
Where Side Sleeping Can Cause Problems
Shoulder and Hip Pain
The most common complaint from side sleepers is joint pressure. When you sleep on one side for hours, your full body weight compresses the shoulder and hip underneath you. Over time, this can irritate the bursa, a small fluid-filled sac that cushions the bony point of your hip. The resulting condition, called greater trochanteric pain syndrome, causes hip pain and tenderness that’s often worse at night. Side sleepers who always favor the same side are especially prone to this.
Shoulder pain follows a similar pattern. Prolonged compression can aggravate the rotator cuff and surrounding structures, leading to stiffness or aching when you wake up. If you already have a shoulder injury or impingement, sleeping directly on that side will almost certainly make it worse.
Skin and Wrinkles
Side sleeping presses one half of your face into the pillow for hours at a time. Research from the Aesthetic Society found that this mechanical compression creates “sleep wrinkles” that are distinct from the expression lines caused by smiling or squinting. These wrinkles typically show up on the forehead, lips, and cheeks, and they tend to run perpendicular to your normal expression lines. Because they’re caused by physical compression rather than muscle movement, they can’t be treated with Botox. The only way to prevent them is to reduce the amount of time your face spends pressed against a surface.
Left Side vs. Right Side
For most people, the left side has a slight edge. It’s better for acid reflux, and the brain-clearance research suggests lateral sleeping in general is beneficial. But there’s one notable exception: people with heart failure. Research published in the Journal of the American College of Cardiology found that people with enlarged hearts instinctively avoid sleeping on their left side. In that position, the heart shifts closer to the chest wall, which can cause discomfort from a more prominent heartbeat, increased breathlessness, and greater strain on the cardiovascular system. If you have heart failure, your body may already be steering you away from the left side for good reason.
For everyone else, alternating between sides throughout the night is a reasonable approach. It distributes pressure more evenly across both shoulders and hips and reduces the asymmetric skin compression that contributes to wrinkles on one side of the face.
Side Sleeping During Pregnancy
After about 20 weeks of pregnancy, side sleeping becomes the recommended position. The reason is straightforward: as the uterus grows, lying flat on your back allows it to press on the vena cava, the large vein that returns blood from your lower body to your heart. This compression can reduce blood flow to the placenta. The left side is often suggested because the vena cava runs along the right side of the spine, so left-side sleeping takes pressure off it entirely. That said, physicians at the University of Utah note that the risk from occasional back sleeping is largely theoretical, so if you wake up on your back, there’s no need to panic.
How to Set Up for Better Side Sleeping
The biggest mistake side sleepers make is using a pillow that’s too flat. When you’re on your side, your head is significantly higher off the mattress than when you’re on your back, because your shoulder creates a gap. A pillow that doesn’t fill that gap lets your neck bend downward, pulling your spine out of alignment. Most side sleepers need a pillow with a loft (height) between 4 and 6 inches, with medium-firm to firm support so it doesn’t compress flat overnight. If you have broader shoulders, you’ll need the higher end of that range. If your mattress is soft and lets your shoulder sink in more, you can get away with a slightly lower pillow.
A pillow between your knees makes a meaningful difference for your lower back and hips. Without one, the weight of your top leg pulls your pelvis forward and rotates your spine. A knee pillow keeps your hips parallel and stabilized, distributing weight more evenly and maintaining a neutral spinal position. This is a simple fix that can eliminate morning lower back stiffness for a lot of side sleepers.
Mattress firmness matters too. If your mattress is too firm, it won’t let your shoulder and hip sink in enough, creating pressure points. If it’s too soft, your midsection sags and your spine curves. A medium-firm mattress, or a firmer mattress with a foam topper, tends to work best for side sleepers because it spreads weight more evenly while still supporting the spine. If you’re waking up with hip pain, a firmer surface or a foam topper is worth trying before assuming side sleeping itself is the problem.