(HealthDay News) -- A kidney stone is a hard mass developed from crystals that separate from urine and build up on the inner surfaces of the kidney.
Normally, urine prevents these crystals from forming, but not in all people, says the National Institute of Diabetes and Digestive and Kidney Diseases.
If the stones are small enough, they may pass through the urinary tract. But larger stones may lodge in the urinary tract and cause significant pain.
While doctors do not know precisely what causes kidney stones, certain foods may promote the formation of stones in people who are susceptible.
An easy way to prevent stones is to drink more liquids, optimally water. If you tend to form stones, you should try to drink enough liquids to produce at least two quarts of urine in a 24-hour period, the agency says.