Find out what causes kidney stones. They're usually the result of a build-up of a substance such as calcium, ammonia or uric acid in the body.
Kidney stones are usually formed following a build-up of certain chemicals in the body.
This build-up may be any of the following:
- uric acid – a waste product produced when the body breaks down food to use as energy
- cysteine – an amino acid that helps to build protein
Certain medical conditions can lead to an unusually high level of these substances in your urine.
You're also more likely to develop kidney stones if you don't drink enough fluids.
Recurrent kidney stones
Some people are particularly likely to keep on developing kidney stones, including people who:
- eat a high-protein, low-fibre diet
- are inactive or bed-bound
- have a family history of kidney stones
- have had several kidney or urinary infections
- have had a kidney stone before, particularly if it was before you were 25
- have only one fully working kidney
- have had an intestinal bypass (surgery on your digestive system), or a condition affecting the small intestine, such as Crohn's disease
There's evidence to suggest that certain medications may increase your risk of developing recurrent kidney stones. These include:
- diuretics (used to reduce fluid build-up)
- certain antibiotics
- certain antiretroviral medication (used to treat HIV)
- certain anti-epileptic medication
Types of kidney stones
Kidney stones can develop for a number of reasons. The causes of the four main types of kidney stone are outlined below.
Calcium stones are the most common type of kidney stone and form if there's too much calcium in the urine, which can be due to:
- an inherited condition called hypercalcuria, which leads to large amounts of calcium in urine
- an overactive parathyroid gland (the parathyroid glands help to regulate the amount of calcium in your body)
- kidney disease
- a rare condition called sarcoidosis
- some cancers
Calcium stones are usually either large and smooth or spiky and rough.
Struvite stones are often caused by infections, and they most commonly occur after a urinary tract infection that's lasted a long time.
Struvite stones are more common in women than men.
Uric acid stones
Uric acid stones can form if there's a large amount of acid in your urine. They may be caused by:
- eating a high-protein diet that includes lots of meat
- a condition such as gout that prevents the body breaking down certain chemicals
- an inherited condition that causes higher than normal levels of acid in the body
Cystine stones are the rarest type of kidney stone. They're caused by an inherited condition called cystinuria, which affects the amount of acid that is passed in your urine.