Kidney stones (renal lithiasis, nephrolithiasis) are hard deposits made of minerals and salts that form inside your kidneys.
As we all are aware that waste products in the blood are passed through urine. This filtering process is done by the kidneys as it separates the waste products including minerals and salts, which have to be passed out through urine. Many times, these minerals and salts get stuck in your urinary tract and over a long period, this forms kidney stones. They can vary in size from a ping pong ball to the size of a sugar crystal. They are not noticed till the time they cause a blockage. Sometimes, they cause immense pain if they start breaking or are pushed into the ureters (narrow ducts which lead to the bladder).
Passing kidney stones can be quite painful, but the stones usually cause no permanent damage if they're recognized in a timely fashion. Depending on your situation, you may need nothing more than to take pain medication and drink lots of water to pass a kidney stone. In other instances — for example, if stones become lodged in the urinary tract, are associated with a urinary infection or cause complications — surgery may be needed.