Kidney stones are hard mineral deposits that form inside your kidneys. Once they form, they can do a lot more than just sit there. They can block the flow of urine, stretch the kidney tissue, and cause some of the most intense pain a person can experience. In short, kidney stones can turn a normally smooth process—filtering your blood and making urine—into a painful, sometimes dangerous event.
What Do Kidney Stones Do to Your Body?
Kidney stones do their damage by interfering with the urinary tract. Your kidneys constantly filter waste from your blood and produce urine. That urine travels down two thin tubes called ureters and into your bladder. When a stone forms, it usually starts small. Many small stones pass without you ever knowing they were there.
Problems start when a stone grows large enough to get stuck. The most common trouble spot is the ureter. These tubes are narrow—only about 3 to 4 millimeters wide. A stone that fits through may cause little trouble. A stone that does not fit can block urine flow completely.
When urine backs up behind a blockage, pressure builds inside the kidney. This pressure is what causes the severe pain most people associate with kidney stones. The kidney swells, and the pain can radiate from your side and back down into your groin. This is called renal colic, and it often comes in waves.
Beyond pain, a blocked kidney stops working properly. It cannot filter waste effectively. If the blockage lasts too long, it can cause permanent damage to the kidney tissue. This is why a stone that will not pass is considered a medical emergency, not just a painful inconvenience.
What Are the First Signs a Kidney Stone Is Moving?
The first sign is often sudden, sharp pain. This pain typically starts in your side or lower back, just below your ribs. It may move to your lower abdomen and groin as the stone travels down the ureter. The pain can change in intensity, coming and going in waves as the ureter spasms around the stone.
Other common signs include blood in the urine. The stone scrapes against the delicate lining of the urinary tract as it moves. That scraping causes bleeding, which can make your urine pink, red, or brown. You may also feel a constant need to urinate, or you might urinate more often than usual.
Nausea and vomiting are also common. The kidney and the stomach share nerve pathways. When a stone stretches the kidney, those nerves can trigger the nausea reflex. Some people describe feeling like they have the flu, with chills and a general sense of being unwell.
Fever and chills are a different matter. A fever with a kidney stone can mean an infection is present. An infected blocked kidney is a life-threatening situation. If you have a fever with stone pain, you need emergency care immediately.
How Big Can Kidney Stones Get?
Kidney stones vary enormously in size. Some are as small as a grain of sand. Others can grow to the size of a golf ball, though this is rare. The size matters because it directly affects whether the stone can pass on its own.
Stones smaller than 5 millimeters usually pass without medical help. The ureter can stretch enough to let them through. Stones between 5 and 10 millimeters are more difficult. They may pass, but they often get stuck and require intervention. Stones larger than 10 millimeters rarely pass on their own. They almost always need a procedure to break them up or remove them.
Location also matters. A stone in the kidney itself may cause no symptoms at all. Many people walk around with kidney stones for years and never know it. The trouble begins when the stone moves into the ureter. That is where the narrow passages create problems.
Shape matters too. A smooth round stone moves more easily than a jagged one. Some stones develop sharp edges or spiky projections called staghorn calculi. These can fill the entire kidney shape and cause severe damage if left untreated.
Can Kidney Stones Cause Long-Term Damage?
Yes, but not always. A single small stone that passes quickly usually leaves no lasting damage. The body heals the scraped tissue, and kidney function returns to normal. The bigger risk comes from stones that block urine flow for extended periods.
Prolonged blockage causes hydronephrosis—a condition where the kidney swells because urine cannot drain. If this lasts more than a few weeks, the pressure can damage the nephrons, the tiny filtering units inside the kidney. This damage can be permanent.
Recurrent stones also take a toll. Each stone that passes scrapes the urinary tract. Over time, this can cause scarring. Scar tissue in the ureter can narrow the passage, making future stones more likely to get stuck. Some research suggests that people who form stones repeatedly have a higher risk of chronic kidney disease.
Infections add another layer of risk. A stone can harbor bacteria even when it is not causing symptoms. These bacteria can cause repeated urinary tract infections. If an infection spreads to the kidney itself, it can cause permanent damage or, in severe cases, sepsis.
What Happens If a Kidney Stone Is Left Alone?
It depends on the stone. Many stones do nothing. They stay in the kidney, causing no pain and no problems. Doctors often find these incidentally during scans for other conditions. These silent stones may never need treatment.
Other stones eventually pass. The body pushes them out through the ureter, into the bladder, and out through the urethra. This process can take days or weeks. It is uncomfortable, but it resolves on its own.
The dangerous scenario is a stone that blocks the ureter completely. Urine has nowhere to go. The kidney swells. Waste products build up in the blood. If this continues, the kidney can fail. This is why doctors take a completely blocked ureter seriously. They do not wait to see if it resolves.
A stone that stays in the ureter for more than a few weeks can also cause the ureter to narrow around it. This stricture can persist even after the stone is removed. It may require additional surgery to correct.
How Are Kidney Stones Treated?
Treatment depends on size, location, and symptoms. Small stones are usually managed with fluids and pain medication. Your doctor may give you a medication called an alpha-blocker, which relaxes the ureter and helps the stone pass faster. This approach is called conservative management, and it works for most small stones.
For stones that do not pass, several procedures exist. Shock wave lithotripsy uses sound waves to break the stone into smaller pieces that can pass in urine. This is non-invasive and works well for stones in the kidney or upper ureter. It does not work as well for very hard stones or stones in the lower ureter.
Ureteroscopy is another option. A thin scope goes up through the urethra and bladder into the ureter. The doctor can see the stone and either remove it with a small basket or break it with a laser. This is the most common procedure for stones stuck in the ureter.
Percutaneous nephrolithotomy is reserved for very large stones. The surgeon makes a small incision in your back and removes the stone directly from the kidney. This is the most invasive option, but it is the most effective for stones larger than 2 centimeters.
Can You Prevent Kidney Stones From Forming?
Prevention starts with understanding what kind of stone you have. The most common type is calcium oxalate. About 80 percent of stones fall into this category. Other types include uric acid stones, struvite stones, and cystine stones. Each type has different triggers and different prevention strategies.
For calcium oxalate stones, the most important step is drinking enough water. The goal is to produce at least 2 to 2.5 liters of urine per day. Diluted urine makes it harder for crystals to form and clump together. This single step reduces stone risk more than any other measure.
Dietary changes can help, but the advice is not what most people expect. Limiting calcium is usually wrong. In fact, getting enough dietary calcium helps bind oxalate in the gut before it reaches the kidneys. The real culprits are often excess sodium and excess animal protein. Both increase the amount of stone-forming substances in urine.
Some people benefit from medication. Thiazide diuretics reduce calcium in urine. Allopurinol lowers uric acid levels. Potassium citrate makes urine less acidic, which discourages stone formation. These medications are reserved for people who form stones repeatedly despite lifestyle changes.
Frequently Asked Questions
Can a kidney stone cause permanent kidney damage?
Yes, if it blocks urine flow for weeks, the pressure can permanently damage kidney tissue. A single small stone that passes quickly usually causes no lasting harm.
How long does it take to pass a kidney stone?
Most stones that pass on their own do so within 2 to 3 weeks of symptoms starting. Smaller stones tend to pass faster than larger ones.
What does kidney stone pain feel like compared to other pain?
It is typically a sharp, cramping pain that comes in waves and moves from the side or back down toward the groin. Many people describe it as the worst pain they have ever felt.
Is a 5 mm kidney stone considered large?
Yes, 5 millimeters is the size threshold where stones often struggle to pass on their own. Stones at this size may still pass, but they have a higher chance of getting stuck.
