symptom of kidney stones ; What causes kidney stones?

Kidney stones form when the salts and minerals that are normally found in the urine become out of balance. Different kinds of kidney stones are formed from salts in the urine.

Calcium stones
These are the most common type of kidney stones. They are made of calcium and oxalate, which are chemicals found naturally in certain foods (see "Prevention", below for examples of these foods). A diet with a high content of calcium and oxalate can increase the concentration of these chemicals in the urine and make it more likely for stones to form. Other factors include:

excess vitamin D,
overactive parathyroid glands,
medical conditions such as cancer, some kidney diseases, or a disease called sarcoidosis.
Uric acid stones
Excess amounts of uric acid can be caused by eating a lot of meat. Conditions such as gout and treatments such as chemotherapy can also increase the risk of getting uric acid stones.

Struvite stones (infection stones)
These are caused by too much ammonia in the urine. Ammonia is a chemical produced by the bacteria that cause urinary tract infections. This kind of stone is most often found in women.

Cystine stones
These are caused by a hereditary disorder called cystinuria, which affects about one per cent of men and women.

National Kidney Federation (UK)
0845 6010209