What are kidney stones?
Kidney stones are hard, stone-like lumps that can form in the kidneys when waste products in the urine become highly concentrated and crystallise. They can range in size from tiny grains to, rarely, several centimetres across. Small stones may pass out of the body in the urine unnoticed, but larger ones can get stuck and cause significant pain and other symptoms as the body tries to pass them.
Kidney stones are common, and some people are more prone to forming them than others. While they can be extremely painful, they do not usually cause lasting damage if treated promptly. Understanding why they form helps both in treating them and, importantly, in preventing them from coming back, which is a key goal since people who have had one stone are at higher risk of more.
Symptoms
Small kidney stones often cause no symptoms and pass unnoticed. Larger stones, or those that move into the tube connecting the kidney to the bladder, can cause sudden and severe symptoms. These include:
- •Severe pain in the side, back, lower tummy or groin, often in waves
- •Pain that may come and go and shift as the stone moves
- •Blood in the urine, which may look pink, red or brown
- •Feeling sick or being sick
- •A frequent or urgent need to urinate
- •Pain or difficulty passing urine
- •Fever and chills, if there is also an infection
Causes and risk factors
Kidney stones form when there is too much of certain waste substances in the urine and not enough fluid to dilute them, allowing crystals to form and build up. There are different types of stones, the most common being calcium stones. Several factors increase the risk:
- •Not drinking enough fluids, so urine becomes concentrated
- •A diet high in salt, or in certain substances depending on stone type
- •Being overweight
- •A family or personal history of kidney stones
- •Certain medical conditions and some medications
- •Living in a hot climate or sweating heavily without replacing fluids
Treatment
Treatment depends on the size and type of the stone. Small stones can often be passed at home by drinking plenty of fluids, with pain relief to manage the discomfort, and sometimes medication to help the stone pass more easily. Passing a stone can take days to weeks, and the urine may be strained to catch it for analysis, which helps guide prevention.
Larger stones, or those causing severe symptoms, a blockage or infection, may need a procedure. Options include shockwave treatment, which breaks the stone into smaller pieces from outside the body, and procedures using thin instruments to remove or break up the stone. A stone causing a blockage with infection is a medical emergency needing prompt treatment. A doctor will advise on the best approach.
Preventing kidney stones
Because people who have had a kidney stone are at higher risk of forming more, prevention is an important part of care. The single most effective measure for most people is drinking plenty of fluids throughout the day, especially water, to keep the urine dilute and discourage stones from forming. Aiming to keep urine pale is a useful guide.
Dietary measures can also help, and the right advice depends on the type of stone you form. General steps include not having too much salt, maintaining a healthy weight, and moderating certain foods depending on stone type. Because the most effective prevention depends on the stone's composition, it is worth discussing a personalised plan with a doctor, especially after a first stone, to reduce the chance of recurrence.
The different types of kidney stones
Not all kidney stones are the same, and knowing which type you form matters because it shapes the most effective prevention. Stones are made of different substances, and analysing a passed stone allows a doctor to tailor advice rather than giving generic guidance.
Calcium stones are by far the most common, usually made of calcium oxalate. Interestingly, the answer is not simply to cut out calcium — adequate dietary calcium can actually help, while it is other factors, including certain high-oxalate foods and low fluid intake, that often matter more. Other types include uric acid stones, which are linked to diet and conditions like gout, struvite stones, which are associated with urinary infections, and rarer cystine stones, which have a genetic cause.
Because each type responds to different preventive measures, having a passed stone analysed is genuinely useful. It allows your doctor to give specific dietary and, where appropriate, medical advice aimed at your particular type of stone, which is far more effective than general measures alone for people who form recurrent stones.
Diet and fluids for stone prevention
Diet and fluid intake are central to preventing kidney stones, and getting them right can substantially reduce the chance of forming new stones. Fluid is the most important factor for almost everyone: drinking enough to keep urine dilute and pale dilutes the substances that form stones. Most people benefit from drinking consistently through the day rather than large amounts at once, and increasing intake further in hot weather or with heavy exercise.
Dietary advice depends on stone type, but some general principles help many people. Reducing salt is widely beneficial, as high salt increases the calcium in urine. Maintaining a healthy weight helps, and for calcium-oxalate stones, moderating very high-oxalate foods while keeping adequate dietary calcium is often advised. For uric acid stones, reducing certain rich foods and managing related conditions helps.
Because the specifics vary so much by stone type, the most effective approach is a personalised plan from a doctor or dietitian, particularly after a first or recurrent stone. Generic advice helps, but tailored guidance based on your stone's composition and any underlying factors gives the best protection against future stones.