What Are Flat Feet? Causes, Symptoms, and What to Do About Them
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If you've been told you have flat feet — or if you've noticed your arches don't seem to have any height when you stand — you may have questions about what that actually means for your long-term health. Flat feet are one of the most common structural foot variations, affecting an estimated 20–30% of adults. For many people, they cause no problems at all. For others, flat feet are the root cause of foot pain, knee pain, hip discomfort, and chronic fatigue — problems that don't resolve on their own because the underlying mechanics never change.
This article explains what flat feet are, what causes them, what symptoms they produce, and what interventions actually make a difference.
What Are Flat Feet?
The medical term is pes planus. It describes a foot where the arch — the curved area along the inner edge of the foot between the heel and the ball — is significantly reduced or absent. When you stand, the entire sole of your foot makes contact with the ground rather than the arch lifting off it.
There are two main types:
Flexible flat feet. The arch appears normal when the foot is off the ground or when you stand on your toes, but collapses when bearing full weight. This is the most common type. The arch structures are present; they just don't maintain height under load.
Rigid flat feet. The arch is absent in all positions — whether weight-bearing or not. This is less common and is often associated with structural abnormalities in the bones, tendons, or joints of the foot.
A third category is acquired flat feet, which develops in adulthood when the arch was previously present. This is most often caused by posterior tibial tendon dysfunction (PTTD) — a gradual failure of the tendon that runs along the inner ankle and actively supports the arch.
What Causes Flat Feet?
Flat feet can be congenital (present from birth) or can develop over time. The main causes:
Genetics. The most common cause. Arch height is largely inherited. If one or both parents have flat feet, the likelihood of having them is significantly higher. The foot's arch is determined by bone structure, tendon elasticity, and ligament tension — all of which are genetically influenced.
Normal childhood development. All infants have flat feet. The arch typically develops between ages 3 and 6 as the fat pad on the inner foot thins and the bones, tendons, and muscles mature. In some children, the arch never fully develops.
Posterior tibial tendon dysfunction. The posterior tibial tendon runs from the calf muscle along the inside of the ankle to the arch. Overuse, age, or injury can weaken or tear this tendon, causing the arch to fall progressively. This is the most common cause of adult-acquired flat feet.
Obesity and sustained overload. Prolonged mechanical stress on the arch — from excess weight, standing for hours on hard surfaces, or carrying heavy loads — can gradually flatten it over time.
Hypermobility. Generalized ligamentous laxity (loose joints throughout the body) makes it difficult for the foot to maintain arch height under load.
Injury. Trauma to the bones or tendons of the foot — particularly the spring ligament or plantar fascia — can reduce arch integrity.
What Symptoms Do Flat Feet Cause?
Many people with flat feet are asymptomatic — they have the structural variation but no pain or functional limitation. For others, flat feet produce a range of symptoms, often felt not just in the foot but further up the kinetic chain:
Foot and ankle pain. Pain along the inner arch, under the heel, or around the inner ankle. Often worse after long periods of standing or walking.
Overpronation. Flat feet cause the ankle to roll inward (pronate) during the gait cycle. Overpronation increases stress on the Achilles tendon, calf muscles, inner knee, and hip.
Knee pain. The inward rolling of the foot twists the shin bone inward, which shifts the knee medially. This alters knee mechanics and can cause patellofemoral pain (pain behind the kneecap) or medial knee stress.
Hip and lower back pain. Altered mechanics at the foot and knee translate upward. Flat feet are often a contributing factor in hip and low back pain, particularly in people who stand or walk for long hours. See our article on flat feet and back pain →
Fatigue. Flat feet make muscles work harder to maintain stability during gait. Foot and leg fatigue — especially after long days on your feet — is a common complaint.
Calluses. Abnormal pressure distribution from flat feet produces calluses along the inner edge of the foot, the heel, and the ball of the foot.
How Are Flat Feet Diagnosed?
Diagnosis is primarily visual and functional:
Footprint test. The wet footprint test is a simple self-assessment. Wet the soles of your feet, step on a flat surface (cardboard or paper), and look at the impression. A normal arch leaves a gap on the inner edge; a flat foot leaves a full or nearly full print.
Clinical assessment. A podiatrist or orthopedic specialist assesses arch height both at rest and under load, observes your gait, and evaluates ankle alignment. They will also test the posterior tibial tendon for weakness or pain.
Imaging. X-rays are used when bone structure or alignment needs assessment — particularly for rigid flat feet or when surgery is being considered.
When Do Flat Feet Require Treatment?
Flat feet that cause no symptoms typically don't require intervention. Treatment is appropriate when:
- There is pain in the foot, ankle, knee, hip, or lower back that correlates with flat foot mechanics
- Overpronation is visibly severe and contributing to gait problems
- The arch is actively collapsing (progressive adult-acquired flat feet)
- Foot fatigue is limiting daily activity or work capacity
- Conservative measures (supportive footwear, stretching) haven't provided sufficient relief
What Treatments Work?
Supportive footwear. Shoes with firm heel counters, adequate midsole support, and a moderate heel-to-toe drop (8–12mm) reduce the demand on the arch and slow overpronation. Stability or motion-control running shoes are designed specifically for this. Flip-flops, flat sandals, and minimalist shoes do the opposite.
Stretching and strengthening. Tight calves and weak foot intrinsic muscles both worsen flat foot mechanics. Calf stretching, arch strengthening exercises (short foot exercise, toe spreading, single-leg calf raises), and hip abductor strengthening can reduce overpronation at the source. These don't change bone structure, but they can improve functional arch height.
Custom orthotics. Custom orthotic inserts are made from an impression of your actual foot and designed to support your specific arch height, control your degree of pronation, and distribute load more evenly across the foot. For symptomatic flat feet, custom orthotics are consistently the most effective conservative intervention — because they address the specific biomechanics of your foot rather than a statistical average. See why custom orthotics work better for flat feet →
Surgery. Reserved for severe cases where conservative treatment has failed — particularly for progressive posterior tibial tendon dysfunction or rigid flat feet with bone deformity. Surgical options include tendon repair, ligament reconstruction, and in some cases bone realignment procedures.
Frequently Asked Questions
Do flat feet get worse over time?
Flexible flat feet in adults often remain stable if the feet are well-supported and the load through the arch is managed appropriately. Progressive worsening is more typical of posterior tibial tendon dysfunction, where the tendon actively degrades. If you notice your arch flattening noticeably over months or years, a podiatrist evaluation is warranted.
Can you have flat feet without pain?
Yes. Many people with flat feet are completely asymptomatic throughout their lives. The relationship between arch height and pain is not 1:1 — what matters is whether the structural variation is producing abnormal mechanical stress on nearby tissues.
Are custom orthotics worth it for flat feet?
For people with symptomatic flat feet — pain, fatigue, overpronation-related problems — custom orthotics are generally the most effective conservative treatment. Generic arch supports provide some improvement but don't address your specific arch height and pronation pattern. See which option fits your situation →
How long does it take for orthotics to help?
Most people notice a reduction in fatigue and mild pain within 2–4 weeks of consistent daily wear. Improvement in longer-standing pain patterns typically takes 6–8 weeks. Custom orthotics work through cumulative load correction — the more consistently you wear them, the faster improvement accumulates.
Can flat feet affect children differently than adults?
Yes. Flat feet are normal in children up to about age 6. Most children develop arches naturally without intervention. If flat feet persist past age 6 or are causing pain or abnormal gait, evaluation is appropriate — but many pediatric podiatrists recommend watchful waiting before intervening. See our guide to flat feet in children →
Flat feet are a structural variation, not a disease — but for the people they affect, the mechanical consequences are real and daily. The good news is that the most effective interventions are conservative: supportive footwear, targeted stretching, and orthotics built for how your foot actually loads.
Take the foot assessment to find out if custom orthotics are right for your flat feet →