Kidney stones can be composed of different substances, but the most common ones (80% of stones) consist of calcium salts, mostly in the form of calcium oxalate and calcium phosphate.[1] Less common kidney stones may form from other substances such as medications, struvite, uric acid, or cystine.[2] Kidney stones tend to occur more frequently in men, with an incidence of 10% compared to 5% in women.[3][4]
When a stone is dislodged from the kidney and enters the ureter (the tube that connects the kidney to the bladder), it often causes significant pain by irritating the urether, and sometimes by blocking the normal flow of urine. While most stones pass on their own, they may also block the urinary tract, requiring treatment or surgery for removal. (Most stones are small, <6mm, and pass on their own; larger stones tend to require procedures for removal.)