Bladder cancer is caused by changes to the cells of the bladder. It's often linked with exposure to certain chemicals, but the cause isn't always known.

Several factors have been identified that can significantly increase your risk of developing bladder cancer.

Smoking

Smoking is the single biggest risk factor for bladder cancer. This is because tobacco contains cancer-causing (carcinogenic) chemicals.

If you smoke for many years, these chemicals pass into your bloodstream and are filtered by the kidneys into your urine. The bladder is repeatedly exposed to these harmful chemicals, as it acts as a store for urine. This can cause changes to the cells of the bladder lining, which may lead to bladder cancer.

It's estimated that more than a third of all cases of bladder cancer are caused by smoking. People who smoke may be up to 4 times more likely to develop bladder cancer than non-smokers.

Exposure to chemicals

Exposure to certain industrial chemicals is the second biggest risk factor. Previous studies have estimated that this may account for around 25% of cases.

Chemicals known to increase the risk of bladder cancer include:

• aniline dyes
• 2-Naphthylamine
• 4-Aminobiphenyl
• xenylamine
• benzidine
• o-toluidine

Occupations linked to an increased risk of bladder cancer are manufacturing jobs involving:

• dyes
• textiles
• rubbers
• paints
• plastics
• leather tanning

Some non-manufacturing jobs have also been linked to an increased risk of bladder cancer. These include taxi or bus drivers, as a result of their regular exposure to the chemicals present in diesel fumes.

The link between bladder cancer and these types of occupations was discovered in the 1950s and 1960s. Today, strict regulations limit exposure to cancer-causing chemicals.

However, these chemicals are still linked with cases of bladder cancer now, as it can take up to 30 years after initial exposure to the chemicals before the condition starts to develop.

Other risk factors

Other factors that can increase your risk of bladder cancer include:

• radiotherapy to treat previous cancers near the bladder, such as bowel cancer
• previous treatment with certain chemotherapy medications, such as cyclophosphamide and cisplatin
• having certain treatments for type 2 diabetes
• having a tube in your bladder (an indwelling catheter) for a long time, because you have nerve damage that has resulted in paralysis
• long-term or repeated urinary tract infections (UTIs)
• long-term bladder stones
• an untreated infection called schistosomiasis (bilharzia), which is caused by a parasite that lives in fresh water – this is very rare in the UK

Bladder cancer usually begins in the cells of the bladder lining. In some cases, it may spread into surrounding bladder muscle. If the cancer penetrates this muscle, it can spread to other parts of the body, usually through the lymphatic system.

If bladder cancer spreads to other parts of the body, such as other organs, it's known as metastatic bladder cancer.