Kidney stones are deposits of hard material, varying in size, that may form and collect within the kidneys and pass into the urethra (the tubes that carry urine to the bladder). The deposits are composed of calcium phosphates, calcium oxalate, ammonium phosphate, calcium carbonate, uric acid or urates.

Symptoms include an occasional severe stabbing pain in the back, and nausea. There may be a slight amount of blood in the urine. The causes are a high level of calcium in the urine, a change in acidity or alkalinity of the urine, concentration of the urine due to excessive sweating or reduced fluid intake. Factors like gout, kidney infection, a diet deficient in vitamin A, an overactive parathyroid gland and even a genetic history may lead to the formation of stones.