What is the main risk factor for bladder cancer?

Using tobacco, especially smoking cigarettes, is a major risk factor for bladder cancer. A risk factor is anything that raises the chance of getting a disease.

It is not a close contest. The National Cancer Institute calls smoking by far the greatest known environmental risk factor for bladder cancer. People who smoke have four to seven times the risk of people who never smoked.

Why the bladder, of all places

The link seems odd until you follow the chemicals. Smoke carries carcinogens into the lungs, and from there into the blood. The kidneys filter the blood and pull those chemicals into the urine. The urine then sits in the bladder for hours at a time.

That storage step is the whole point. The bladder lining gets a long, repeated soak in concentrated carcinogens, which damages the DNA of the cells lining it. Over decades, that damage adds up.

The same logic explains the other big risk factor. Certain workplace chemicals travel the same route. NCI lists exposure to paints, dyes, metals, and petroleum products. The classic culprits are aromatic amines, once heavily used in the rubber, dye, leather, and printing trades. NCI's screening summary estimates that 5% to 15% of people in the US who eventually die of bladder cancer have strong histories of exposure to environmental factors other than smoking.

The rest of the list

Other recognized risk factors include:

• Arsenic in well water, and chlorinated drinking water
• Long-term infection with Schistosoma haematobium, a parasite found in parts of Africa and the Middle East
• Long-term use of a urinary catheter, or repeated bladder infections
• The chemotherapy drugs cyclophosphamide and ifosfamide
• Past radiation therapy to the pelvis
• The Chinese herb Aristolochia fangchi
• Family history

Age and sex matter too, though neither is something you can act on. The median age at diagnosis is 73. In the US, men are diagnosed at about 31.0 cases per 100,000 people per year, compared with 7.6 for women. That is roughly a fourfold gap.

The sign that should not wait

Blood in the urine, called hematuria, is the most common first sign. It shows up in about 90% of bladder cancer cases.

Two things make it easy to miss. It is usually painless, so it does not feel urgent. And it often comes and goes, so people wait to see whether it returns.

Blood in the urine deserves a call to a doctor even if it happens once and clears. That is true whether you can see it or a lab test found it.

The reassuring flip side: most hematuria is not cancer. Roughly 13% of adults have small amounts of blood in the urine without symptoms, and only about 4.8% of those turn out to have bladder cancer. The point of getting checked is to sort your case into the large group, not to assume the worst.

What to do with this

There is no screening test recommended for bladder cancer in people at average risk. NCI's review found the evidence inadequate to show that screening lowers deaths, and screening a healthy population would trigger many unnecessary procedures.

So prevention here is mostly about exposure. Quitting smoking is the single largest lever. Free help is available through smokefree.gov and state quitlines.

If you have worked with dyes, rubber, paint, leather, or petroleum products, say so at your next checkup. A work history is the kind of detail a doctor will not know unless you volunteer it, and it changes how a symptom like hematuria gets handled.