A kidney stone refers to a solid piece of material or 'stone' which is found in the urinary tract. There are four main types of kidney stones depending on what material they are made up of - calcium containing stones, uric acid stones, infection stones and cystine stones (very rare). Some of the stones will disappear themselves without treatment as they can be dissolved slowly back into the body (depending on the pH of the urine i.e. how acidic or alkaline the urine is).
Kidney stones form because chemicals (or solutes) come out of solution when a solution is too saturated with that particular chemicals - these chemicals form crystals through 'crystallisation'. The solubility of chemicals differs depending on the pH of the urine and whether substances which inhibit crystallisation such as citrate are present. Sometimes stones can be caused by other things, such as a problem with the hyper-parathyroid gland, a small gland found in your body. This causes the blood level of calcium to be too high.
Many people do not know that they have kidney stones as the stones sit in the kidney and do not cause any harm. They may not grow for many years and they may not move.
With modern x-rays, very tiny stones can sometimes be seen in the kidney - these do not always need to be treated as they may be too small to treat.
If you do get kidney stones which require treatment, there are different treatment options available depending on the size of the stone and where it is found in the urinary tract. Some drugs in combination with drinking plenty of water can help dissolve uric-acid stones. In fact, making your urine as dilute as possible by drinking lots of fluid, is the best way to stop stones forming. Depending on which type of kidney stones you get, there are also some changes you can make to your diet to help stop stones forming.