A rib flare is when the lower edges of your ribcage visibly protrude outward instead of sitting relatively flat against your torso. It affects the bottom ribs and the costal margin, the curved cartilage border that connects your lower ribs to your breastbone. You might notice it when you look in a mirror, lie on your back, or raise your arms overhead. It can appear on one side (more commonly the left) or both, and it ranges from barely noticeable to quite prominent.
What Causes Rib Flare
Rib flare isn’t a single condition with one cause. It can develop from structural differences in the chest wall, from postural habits, from pregnancy, or from a combination of all three. Understanding which category yours falls into helps determine whether it needs attention and what kind.
In some people, rib flare accompanies chest wall deformities like pectus excavatum (a sunken breastbone) or pectus carinatum (a protruding breastbone). In these cases, the lower ribs get pulled upward and pushed outward as part of the overall shape of the chest. Rib flaring is frequently perceived as the most prominent feature of these deformities, even when the pectus itself is relatively mild. But rib flare can also appear entirely on its own, without any other chest wall abnormality.
Posture plays a significant role, especially for people without a structural deformity. When your pelvis tilts forward and your lower back arches excessively, your ribcage tips upward and the lower ribs fan outward. This is sometimes called an “open scissors” posture because the angle between your ribs and pelvis widens. In this scenario the flare is largely positional, meaning the ribs themselves aren’t malformed but are being held in a flared position by muscle imbalances and habitual alignment.
Rib Flare During and After Pregnancy
Pregnancy is one of the most common triggers for rib flare. Over roughly ten months, your ribcage gradually widens to accommodate a growing uterus and the internal organs it displaces. Your diaphragm gets pushed upward, and your ribs widen and flare outward so you can continue to breathe effectively despite the reduced space. This is a normal, necessary adaptation.
After delivery, the ribs typically return to their pre-pregnancy position within a few months. But for some women, the flare persists. This usually happens when the core muscles that help pull the ribs back into alignment, particularly the deep abdominals and the muscles along the sides of the ribcage, haven’t regained their strength or coordination. Persistent rib flare postpartum often overlaps with diastasis recti, the separation of the abdominal muscles that also results from pregnancy-related expansion.
How Rib Flare Affects Breathing
Your diaphragm attaches to the inside of your lower ribs in an area called the zone of apposition. When you inhale, the diaphragm contracts and pushes downward, and the pressure it generates gets transmitted through this zone to expand your lower ribcage outward and draw air into your lungs. This is the normal mechanics of a deep, efficient breath.
When your ribs are already flared, the zone of apposition shrinks. The diaphragm loses some of its mechanical advantage because the lower ribs are already splayed wide. The result is that your breathing becomes shallower and more reliant on your neck and upper chest muscles, which are less efficient. You may not notice this consciously, but it can contribute to neck tension, shoulder tightness, and a feeling that you can’t take a fully satisfying breath. Restoring a more neutral rib position helps the diaphragm work the way it’s designed to.
How to Tell If You Have It
The simplest test is to lie flat on your back and look at your lower ribcage. If the bottom edges of your ribs point noticeably toward the ceiling rather than sitting relatively flush, you likely have some degree of flare. You can also place your hands on the lower edges of your ribcage and feel whether the cartilage border angles sharply outward.
Another way to check is the infrasternal angle, the V-shaped opening at the bottom of your ribcage where the left and right costal margins meet. In a neutral ribcage, this angle is roughly 90 degrees. In a flared ribcage, it opens wider, sometimes significantly. Comparing how your ribs look when you exhale fully versus when you’re relaxed can also be telling. If the flare reduces dramatically on a complete exhale, that suggests a strong postural and muscular component rather than a fixed structural one.
Exercises That Help Reduce Rib Flare
For postural and muscular rib flare, targeted exercises can make a real difference. The key muscles to strengthen are the serratus anterior (which wraps around your ribcage from your shoulder blade to your ribs) and your obliques (the side abdominal muscles that pull the lower ribs downward and inward). Equally important is learning to use your diaphragm effectively so your breathing reinforces a neutral rib position rather than working against it.
Scapular push-ups are one of the most effective serratus anterior exercises. Get into a plank position with straight arms, then let your chest sink slightly between your shoulder blades. Push back up by rounding your upper back as if pushing the floor away from you. Your elbows stay straight the entire time. Two to three sets of 10 to 15 reps is a good starting point.
Wall slides target both the serratus anterior and the muscles that control rib position during overhead movement. Stand with your back against a wall, arms bent at 90 degrees with your forearms flat against the surface. Slide your arms up the wall while actively pressing your entire back into the wall behind you. This forces your ribs to stay down rather than flaring as your arms rise. Two to three sets of 10 to 12 reps works well.
Breathing drills tie everything together. Lie on your back with a small rolled towel between your shoulder blades and focus on expanding your ribcage sideways as you inhale, not upward. On the exhale, actively draw your ribs down and together, feeling your obliques engage. This retrains the coordination between your diaphragm, your core muscles, and your rib position. Even five minutes of focused practice daily can shift your resting rib position over several weeks.
When Rib Flare Is Structural
If your rib flare is caused by an underlying chest wall deformity, exercise alone won’t fully resolve it. The cartilage and bone are shaped in a way that holds the ribs in a flared position regardless of muscle strength. That said, improving core strength and breathing mechanics can reduce the visual prominence of the flare and address any associated discomfort or breathing inefficiency.
For cases that cause significant cosmetic concern or functional problems, surgical options exist. These typically involve reshaping or removing portions of the costal cartilage. This is more commonly pursued when the flare accompanies a pectus deformity that’s being corrected at the same time. Isolated rib flare without any symptoms or functional limitation is generally considered a normal anatomical variation rather than a medical problem requiring treatment.