Kidney stones are hard mineral deposits that form inside your kidneys when your urine contains more crystal-forming substances than your fluid can dilute. Your kidneys normally remove waste products in urine, but when the balance of water, minerals, and salts shifts, those substances can stick together and slowly grow into stones. Understanding why this happens is the first step in preventing the intense pain these stones can cause.
What Are Kidney Stones Made Of?
Most kidney stones are made of calcium combined with oxalate or phosphate. Calcium oxalate stones are by far the most common type, accounting for about 80% of all kidney stones.
Other stone types include struvite stones, which form after certain urinary tract infections, and uric acid stones, which develop when your urine is too acidic. A less common type, cystine stones, forms in people with a rare inherited condition.
Knowing the stone type matters because prevention strategies differ. A stone made of uric acid requires different dietary changes than one made of calcium oxalate. If you pass a stone, having it analyzed gives your doctor the information needed to recommend the right prevention plan.
Why Do Kidney Stones Form?
Kidney stones form when urine becomes supersaturated, meaning it holds more dissolved minerals than it can keep in solution. Think of adding sugar to cold tea — at some point, the sugar stops dissolving and settles at the bottom. The same principle applies inside your kidneys.
Several factors push urine toward this state. Not drinking enough fluid is the most common contributor. When urine is concentrated, minerals are more likely to crystallize. Low urine volume means the same amount of waste is carried in less water, increasing the concentration of stone-forming substances.
Urine chemistry also plays a role. Some people naturally excrete more calcium, oxalate, or uric acid in their urine. Others have urine that lacks enough natural inhibitors, such as citrate, which normally helps prevent crystals from forming.
What Increases Your Risk of Kidney Stones?
Several risk factors are well established. Dehydration tops the list. People who live in hot climates, work outdoors, or simply do not drink enough water face higher risk.
Diet matters, but not always in the way you might expect. High sodium intake increases the amount of calcium in your urine. Diets very high in animal protein can raise uric acid levels and reduce citrate. Foods high in oxalate, such as spinach, rhubarb, and almonds, can contribute to calcium oxalate stones in susceptible people.
Obesity is linked to a higher risk of kidney stones. So are certain medical conditions, including type 2 diabetes, high blood pressure, and inflammatory bowel disease. A family history of kidney stones roughly doubles your risk.
Some medications increase stone risk. Calcium and vitamin D supplements, certain diuretics, and some medications used to treat migraines or seizures can all raise the odds. Always talk to your doctor about your medications rather than stopping them on your own.
What Does a Kidney Stone Feel Like?
The classic symptom is sudden, severe pain. This pain typically starts in the side or back, below the ribs, and can radiate to the lower abdomen and groin. It comes in waves, fluctuating in intensity as the stone moves through the urinary tract.
Other symptoms include blood in the urine, nausea, vomiting, and a persistent urge to urinate. Fever and chills alongside the pain signal a possible infection and require immediate medical attention.
Small stones may pass without any symptoms at all. You might never know you had one. Larger stones, typically those bigger than 5 millimeters, are more likely to cause blockage and pain.
How Are Kidney Stones Diagnosed and Treated?
Diagnosis usually begins with a description of your symptoms. A CT scan is the most accurate imaging test for detecting kidney stones, though ultrasound is sometimes used first because it avoids radiation exposure. Urine and blood tests help identify the underlying cause.
Treatment depends on stone size and location. Small stones often pass on their own with pain medication and increased fluid intake. Your doctor may prescribe medication to help relax the ureter, the tube connecting the kidney to the bladder, which can speed passage.
For larger stones, several procedures exist. Shock wave lithotripsy uses sound waves to break stones into smaller pieces that can pass in urine. Ureteroscopy involves passing a thin scope through the urinary tract to remove or fragment the stone. Percutaneous nephrolithotomy is a surgical procedure for very large stones, where a small incision in the back allows direct access to the kidney.
These procedures are effective, but they treat the stone, not the underlying problem. Without prevention measures, stones commonly return.
How Can You Prevent Kidney Stones?
Drinking enough fluid is the single most effective prevention strategy. The general goal is to produce about 2 to 2.5 liters of urine per day. Most people need to drink roughly 8 to 10 glasses of water daily to achieve this, though needs vary with climate, activity level, and body size. Your urine should be light yellow, not dark.
Dietary changes depend on stone type, but some general principles apply broadly. Reducing sodium helps lower urinary calcium. Limiting animal protein — especially red meat and organ meats — reduces uric acid production. Getting calcium from food rather than supplements appears protective, because dietary calcium binds to oxalate in the gut before it reaches the kidneys.
If you have had a calcium oxalate stone, your doctor may suggest moderating high-oxalate foods like spinach, beets, nuts, and chocolate — but not eliminating them. Pairing these foods with a calcium source at the same meal can reduce oxalate absorption.
For people with recurrent stones, preventive medications may be appropriate. Thiazide diuretics reduce urinary calcium. Allopurinol lowers uric acid levels. Potassium citrate raises urine citrate, which inhibits stone formation. These medications require a doctor’s evaluation and monitoring.
When Should You See a Doctor?
See a doctor promptly if you have pain that prevents you from sitting still, pain accompanied by fever and chills, blood in your urine, or nausea that prevents you from keeping fluids down. These symptoms can indicate a stone that is not passing or a concurrent infection.
Anyone who has had one kidney stone should discuss prevention with their doctor. A single stone increases the chance of future stones substantially. Without preventive measures, the recurrence rate is roughly 50% within five years.
Your doctor may order a 24-hour urine collection to measure your urine volume, pH, calcium, oxalate, citrate, and uric acid. This test provides the data needed to design a personalized prevention plan. It is the most useful tool for identifying why your body forms stones and what to do about it.
Frequently Asked Questions
Can drinking more water really prevent kidney stones?
Yes, higher fluid intake is the most effective prevention strategy. Producing about 2 to 2.5 liters of urine daily significantly reduces the concentration of stone-forming minerals.
Are kidney stones more common in men or women?
Men have a higher lifetime risk of kidney stones than women, though the gap has narrowed in recent decades. The overall lifetime risk is about 11% for men and 9% for women.
Can certain foods cause kidney stones?
Some foods contribute to stone risk, especially when consumed in excess. High sodium, high animal protein, and very high oxalate intake can all increase risk in susceptible people, but no single food causes stones on its own.
How long does it take to pass a kidney stone?
Small stones may pass within a few days to a few weeks. Stones under 5 millimeters pass on their own about 80% of the time, while larger stones are more likely to require intervention.
