Kidney stones form when minerals and salts that are normally dissolved in urine become concentrated enough to crystallize. These crystals stick together and grow into a solid mass inside the kidney. The most common type is calcium oxalate, though several other types exist. Risk rises with dehydration, certain diets, some medical conditions, and a family history of stones. Roughly one in ten people will have a kidney stone at some point in their life, and about half of those who get one will get another within five to ten years.
How Do Kidney Stones Form Causes Types And Risk?
Urine is mostly water, but it also carries dissolved waste products. When the balance of water and waste shifts, those dissolved minerals can stop staying dissolved. They clump into tiny crystals. Over weeks or months, crystals can build up into a stone.
Two things usually drive this process. The first is low urine volume — not enough water to keep waste diluted. The second is too much stone-forming material in the urine, or too little of the substances that normally block crystals from forming.
Your body makes natural inhibitors that slow crystallization. Citrate is one of them. When citrate levels in urine drop, calcium stones become more likely. This is one reason some kidney stone problems are not simply about drinking more water.
Stones can form anywhere in the urinary tract, but most begin in the kidney. They may stay there without symptoms, or they may move into the ureter — the narrow tube connecting kidney to bladder — where they cause the pain most people associate with kidney stones.
What Are the Different Types of Kidney Stones?
Not all stones are the same. The type matters because it changes what caused the stone and how a doctor may try to prevent another one.
- Calcium oxalate — the most common type. Forms when urine has too much oxalate or calcium, or too little citrate and water.
- Calcium phosphate — linked to certain metabolic conditions and sometimes to urine that stays too alkaline.
- Uric acid — forms when urine is persistently acidic. More common in people with gout, diabetes, or a high-purine diet.
- Struvite — associated with certain urinary tract infections caused by bacteria that produce urease. These can grow quickly and become large.
- Cystine — rare, and caused by an inherited condition called cystinuria. These tend to recur.
Knowing the type requires catching the stone or testing the urine. Many people pass a stone and never find out what it was made of, which makes prevention harder to tailor.
What Causes Kidney Stones to Form?
Dehydration is the single most common driver. When you do not drink enough, urine becomes concentrated and minerals are more likely to crystallize. This is why stones are more common in hot climates and during warmer months.
Diet plays a role, but not always in the way people expect. A common myth is that cutting calcium prevents calcium stones. The opposite is often true. Eating normal amounts of calcium with meals can actually reduce oxalate absorption in the gut, which lowers oxalate in the urine. Restricting dietary calcium too much may raise stone risk rather than lower it.
Other contributors include:
- High sodium intake, which increases calcium in the urine
- High oxalate intake from foods like spinach, rhubarb, and nuts — though this matters more for some people than others
- High animal protein, which can raise uric acid and lower citrate
- Obesity and insulin resistance
- Certain medications, including some diuretics and calcium supplements taken without food
- Medical conditions such as gout, hyperparathyroidism, and recurrent urinary tract infections
Family history matters too. If a close relative has had stones, your risk is higher. Some of this is genetic, and some is shared diet and lifestyle.
What Raises Your Risk of Kidney Stones?
Some risk factors you cannot change. Others you can. The list below reflects what clinical research consistently shows.
| Risk factor | Can it be changed? |
|---|---|
| Low fluid intake | Yes |
| High sodium diet | Yes |
| Obesity | Yes |
| Family history | No |
| Prior kidney stone | No |
| Certain medical conditions | Sometimes |
| Some medications | Sometimes |
Having one stone is the strongest predictor of having another. About half of people who form a stone will form another within five to ten years, though the exact rate varies by individual and by stone type.
Men have historically had higher rates of kidney stones than women, though the gap has narrowed in recent decades. Some research suggests this shift may relate to changes in diet and rising obesity rates, but the reasons are not fully settled.
What Are the Symptoms of a Kidney Stone?
A stone sitting quietly in the kidney often causes no symptoms at all. Many are found by accident on imaging done for another reason.
When a stone moves into the ureter, symptoms usually start. The classic symptom is severe, cramping pain that comes in waves — often called renal colic. It typically starts in the back or side, below the ribs, and may radiate toward the lower abdomen or groin as the stone travels.
Other common symptoms include:
- Blood in the urine, which may be pink, red, or only visible under a microscope
- Nausea and vomiting
- Painful or frequent urination
- A persistent urge to urinate
- Fever and chills, which can signal infection and needs urgent care
Fever with a kidney stone is a medical emergency. It can mean the urine is blocked and infected, which can become life-threatening quickly. Anyone with a known or suspected stone plus fever should seek care right away.
How Are Kidney Stones Diagnosed and Treated?
Diagnosis usually starts with a urine test to check for blood or infection, and imaging to confirm the stone and its location. A non-contrast CT scan is the most accurate imaging test for most adults. Ultrasound is often used first in pregnant women and children to avoid radiation.
Treatment depends on the size and location of the stone, and on symptoms.
Small stones — generally those under about 5 millimeters — often pass on their own. Drinking plenty of water and managing pain with medication your doctor recommends is usually the approach. Stones between roughly 5 and 10 millimeters are less likely to pass without help, and those over 10 millimeters usually need a procedure.
Procedures include shock wave lithotripsy, which uses sound waves to break the stone into smaller pieces, and ureteroscopy, which uses a thin scope to remove or break up the stone directly. For very large stones, a surgeon may go through a small incision in the back — a procedure called percutaneous nephrolithotomy.
Your doctor may also prescribe medication to help a stone pass or to lower your risk of forming new ones. Which medication depends on the stone type and the underlying cause.
Can Kidney Stones Be Prevented?
Prevention works best when it is matched to the stone type. The most broadly supported step is drinking enough water. Higher fluid intake is consistently linked to lower stone recurrence, and it is one of the few prevention measures with strong evidence behind it.
Other steps that may help, depending on your situation:
- Reduce sodium. Lower sodium means less calcium in the urine.
- Get calcium from food rather than from supplements taken on an empty stomach.
- Limit animal protein if your doctor recommends it.
- Eat enough fruits and vegetables, which can raise urine citrate.
- For uric acid stones, reducing high-purine foods like organ meats and some seafood may help.
What does not have strong evidence? Routine high-dose vitamin C supplements, and cutting calcium from your diet. Neither is supported as a prevention strategy, and calcium restriction may make things worse.
If you have had more than one stone, a doctor may run a 24-hour urine collection to see what is driving your stones. That test can guide specific changes or medications rather than general advice.
Frequently Asked Questions
How long does it take to pass a kidney stone?
Small stones often pass within a few days to a few weeks, though timing varies widely by size and location. Stones that do not move after several weeks or that cause severe symptoms may need a procedure.
Does drinking lemon water help prevent kidney stones?
Lemon and other citrus contain citrate, which can help block calcium stones from forming. Some studies suggest citrus may help, but the evidence is not strong enough to call it a proven prevention method on its own.
Can kidney stones cause permanent kidney damage?
A stone that blocks urine flow for a long time can damage the kidney, especially if infection is present. Most stones that are treated promptly do not cause lasting harm.
Is it safe to fly with a kidney stone?
There is no general rule against flying, but severe pain, vomiting, or fever should be evaluated before travel. If you have a stone causing symptoms, talk to your doctor first.
