Flat feet happen when the arches on the inside of your feet sit low or touch the ground completely when you stand. For most people, the cause is straightforward: you were born with flexible arches that never fully developed, or your arches gradually collapsed over time due to wear, weight gain, or tendon damage. Roughly 20 to 30 percent of the general population has some degree of flat feet, and many never experience pain or problems from it.
Flexible Flat Feet vs. Rigid Flat Feet
The distinction matters because it points to different underlying causes. Flexible flat feet are the most common type. If you sit down and look at your foot with no weight on it, you can see an arch. But the moment you stand up, the arch flattens out under your body weight. This is often something you’ve had since childhood. Most children have flat feet before age six because the arch hasn’t fully formed yet, and in some people it simply never develops the stiffness to hold its shape under load.
Rigid flat feet are different. The arch is absent whether you’re standing or sitting, weight-bearing or not. This type is less common and more likely to cause pain. It can result from a structural problem in the bones of the foot, such as bones that fused together abnormally during development, or from severe long-term tendon damage. If your feet are flat in every position and you’re having pain, that’s worth getting evaluated.
The Tendon That Holds Your Arch Up
The single most important structure supporting your arch is a tendon that runs along the inside of your ankle and attaches under your foot. When this tendon is healthy, it acts like a cable holding a bridge in place. It keeps the arch lifted and helps your foot flex properly with every step.
When this tendon becomes inflamed or starts to break down from overuse, it weakens and can no longer support the arch. Your foot gradually flattens and your ankle may tilt inward. This is the leading cause of adult-acquired flat feet, sometimes called “fallen arches.” Once the arch collapses, your foot bears weight differently, which can shift ligaments and bones out of their normal alignment over time. Left unchecked, this cascade of changes can eventually lead to arthritis in the foot and ankle joints.
People most at risk for this kind of tendon breakdown are middle-aged and older women, especially those with a higher body mass index. Conditions like diabetes and high blood pressure can also weaken the tendon by reducing its blood supply and making it more vulnerable to degeneration.
Weight Gain and Pregnancy
Extra body weight increases the downward force on your arches with every step. Over time, this can stretch and weaken the ligaments and tendons that hold the arch in place. Research consistently links higher BMI to lower arch height, and obesity can worsen the problem by causing fat-related muscle weakness in the foot, which disrupts how forces distribute across the joints.
Pregnancy creates a double hit. Your body produces a hormone called relaxin that loosens ligaments throughout your body to prepare for childbirth. Combined with the weight gain of pregnancy and a shift in your center of gravity, this hormonal loosening can cause your arches to drop. For some women, the change is temporary. For others, especially after multiple pregnancies, the arch height doesn’t fully return.
Other Common Causes
Several other factors can contribute to flat feet developing or worsening over time:
- Age: Tendons and ligaments lose elasticity as you get older, making arch collapse more likely after 40.
- Injury: A fracture, severe sprain, or direct trauma to the foot can damage the structures supporting the arch.
- Inflammatory conditions: Rheumatoid arthritis and similar disorders can attack the joints and tendons of the foot.
- Tight calf muscles: When the calf muscle group is chronically tight, it increases the pulling force on the arch during walking, accelerating tendon strain.
- Genetics: Flat feet run in families. If your parents had low arches, you’re more likely to as well.
How Flat Feet Affect the Rest of Your Body
Flat feet change the way force travels up through your legs. When your arches collapse, your feet tend to roll inward with each step, a pattern called overpronation. That extra inward rolling creates a chain reaction of stress that travels upward. The ligaments on the inside of your knee absorb more strain than they’re designed for. Your hips compensate by shifting their alignment. And your lower back can develop pain as it adjusts to the altered mechanics below.
Not everyone with flat feet experiences these problems. Many people with low arches walk, run, and exercise without any symptoms at all. But if you’re dealing with persistent knee pain, hip discomfort, or lower back soreness alongside flat feet, the two issues may be connected.
A Simple Home Test
You can check your arch type at home with the wet footprint test. Wet the bottom of your foot, then step onto a piece of dark construction paper or a paper bag. Step off and look at the print. If you see a complete footprint with no inward curve along the middle, where the entire sole made contact with the paper, you likely have flat feet. A normal arch leaves a crescent-shaped gap along the inner edge of the print.
This test is surprisingly accurate for identifying arch type in general terms. It won’t tell you why your feet are flat or whether the cause is structural, but it’s a reliable starting point for understanding what you’re working with.
What Actually Helps
If your flat feet don’t cause pain, you generally don’t need treatment. Plenty of people function perfectly well without prominent arches. But if you’re experiencing foot pain, fatigue, or problems higher up the chain, several approaches can make a real difference.
Footwear is the first and easiest change. Shoes that help flat feet share a few key features: built-in arch support to redistribute pressure, a firm midsole to stabilize alignment, a wide toe box to prevent crowding and bunion formation, good cushioning for shock absorption, and a sturdy heel counter to limit that inward rolling. Motion control shoes from brands like Brooks, New Balance, and Asics are designed specifically for overpronators. Some shoes, like those from Vionic, include a built-in orthotic footbed with a deep heel cup.
Custom or over-the-counter orthotic inserts can also provide arch support inside shoes that lack it. For many people, a quality prefabricated insert is enough. Custom orthotics, molded to your specific foot shape, become worth considering when off-the-shelf options aren’t providing relief.
Strengthening exercises target the small muscles in your foot that help support the arch. Towel scrunches (gripping a towel with your toes), calf raises, and short-foot exercises (where you try to shorten your foot by pulling the ball of your foot toward your heel without curling your toes) can all build strength over time. Stretching tight calves is equally important, since calf tightness increases the load on your arch.
For cases involving significant tendon damage or structural deformity that doesn’t respond to conservative measures, surgical options exist to reconstruct the arch or repair the tendon. But most people with flat feet never reach that point.