A kidney stone is formed when a small speck of mineral settles out of the urine into the kidney or the ureter, a tube that links the kidney to the bladder. Additional minerals will stick to the small speck, which develops into stones over time.
There are four main types of kidney stones, classified depending on the chemicals that make up the stones: calcium salts (calcium oxalate, calcium phosphate, mixed calcium oxalate/phosphate), magnesium ammonium phosphate (struvite), uric acid, or cystine. Though rare, certain medications can sometimes form stones after crystallization in the urine. The most common kidney stones are composed of calcium oxalate, which is naturally present in the urine.
Kidney stones are a common cause for hospital visits in North America. It's estimated that about 10% of North Americans will have a kidney stone at least once during their lifetime, most commonly seen in people aged 20 to 50 years old.
The stones are often small and can pass through the urinary system on their own. Kidney stones are more likely to form in hot climates or in the summertime. When people become dehydrated, the minerals in their urine become more concentrated. It then becomes easier for small mineral particles to settle out of the urine and start a kidney stone. Kidney stones are three times more common in men than in women. They also seem to run in families. People who have already had one kidney stone also have a higher than average risk of getting another.