2-Naphthylamine and Cancer

2-Naphthylamine is a man-made chemical. Its CAS number is 91-59-8. Chemists also call it beta-naphthylamine, and OSHA uses that older name in its rules.

At room temperature it is a colorless crystal with a faint smell. It dissolves in hot water, alcohol, ether, and many solvents. It oxidizes in air, and its vapors can explode.

It belongs to a family called aromatic amines, or arylamines. Benzidine is in the same family. So is 4-aminobiphenyl. Several members of this family cause bladder cancer. That pattern is why the whole family is watched so closely.

2-Naphthylamine had three main jobs. It was an intermediate in making dyes. It was an antioxidant in the rubber industry. And it was used to produce 2-chloronaphthylamine.

The dates are specific. It was made commercially in the United States from at least the early 1920s to the early 1970s. In 1955, the last year with production data, four manufacturers made 581,000 kilograms of it. That is 1.3 million pounds in one year. Imports stopped being significant after 1967.

Commercial manufacture and use were banned in the United States in the early 1970s. Since then it has been sold only in small amounts for laboratory research.

The National Toxicology Program lists 2-naphthylamine as known to be a human carcinogen. It has been on that list since the first Report on Carcinogens in 1980. The basis is sufficient evidence in humans. It is not a guess drawn from animals.

The human evidence has three strands:

• Studies of dyestuff workers found raised rates of urinary bladder cancer.
• Studies of chemical workers exposed mainly to 2-naphthylamine found the same.
• At one dyestuff plant, bladder cancer risk rose as exposure rose. That dose-response pattern is what turns a link into a cause.

NTP notes that smoking habits could not explain the raised risk. Many case reports also tie the exposure to bladder cancer in people who made or used it. Our page on bladder cancer covers how that cancer presents and is treated.

Animal studies point the same way. Oral exposure caused bladder cancer in hamsters, dogs, and rhesus monkeys. It caused benign liver tumors in mice. In rats, oral dosing produced a low rate of bladder cancer. Injection into the abdomen produced benign lung tumors in mice.

The chemical also damaged genes across many test systems. NTP lists mutations in bacteria, yeast, insects, plants, human cells, and live animals. Other damage seen included DNA strand breaks, chromosome changes, micronucleus formation, and sister chromatid exchange.

This is the most interesting part of the science, and it explains the whole pattern.

2-Naphthylamine is not harmful as it arrives. The body has to change it first. The liver can send an arylamine down two paths. One path adds a hydroxyl group, using cytochrome P450 enzymes. That step is activation. The other path adds an acetyl group. That step is detox.

The activated form can stick to blood proteins such as hemoglobin and ride around the body. It can also be changed again into reactive compounds. Those are carried to the bladder, where they bind to DNA. Such DNA adducts have been found in bladder and liver cells of exposed dogs.

So the bladder becomes the target. It is where the reactive form ends up and sits. That also explains the long delay. Bladder cancer can surface many years after the exposure ends.

NTP is direct: because production and use are banned, the potential for exposure is low. The specifics:

• Laboratory technicians and scientists who use it in research face the greatest workplace exposure.
• The general population may breathe traces from burning nitrogen-containing organic matter, such as coal furnaces and cigarettes.
• Mainstream smoke from eight US cigarette brands contained 1.5 to 14.1 nanograms per cigarette. Other investigators reported up to 35 nanograms. Sidestream smoke was reported at 67 nanograms per cigarette.
• It occurs as an impurity, at 0.5% or less, in commercially made 1-naphthylamine.
• EPA's Toxics Release Inventory recorded one facility reporting releases from 1998 through 2001. The amounts were none in 1998, 8 pounds in 1999, 15 pounds in 2000, and 265 pounds in 2001.

Two federal surveys sized the exposed workforce. The National Occupational Hazard Survey ran from 1972 to 1974. It estimated 420 workers potentially exposed. The National Occupational Exposure Survey ran from 1981 to 1983. It estimated 275 workers, of whom 265 were women.

The controls are unusually strict, and they are specific enough to check.

OSHA covers it as beta-naphthylamine in 29 CFR 1910.1003, the standard for 13 named carcinogens. Key points:

• A regulated area must be set up wherever it is made, processed, used, repackaged, released, handled, or stored.
• The standard does not apply to solid or liquid mixtures holding less than 0.1% of it by weight or volume.
• Open-vessel operations are prohibited outright.
• Workers must wash hands, forearms, face, and neck on every exit from the regulated area, close to the exit point.
• For handling operations, employers must supply and ensure use of a NIOSH-certified air-purifying half-mask respirator with particulate filters.

Other agencies add their own layers. EPA sets a reportable quantity of 10 pounds under the Superfund law. EPA also lists it as hazardous waste code U168. The Mine Safety and Health Administration allows it only under approved lab conditions, handled by competent persons. The Department of Transportation treats it as a hazardous material with special marking and labeling rules. ACGIH sets no numeric limit. Its guidance is that exposure by all routes should be as low as possible.

For almost everyone, 2-naphthylamine is history, not a live hazard. There is one exception. People who worked in dye, rubber, or chemical plants before the early 1970s may still be at risk, because bladder cancer can appear decades later. That work history is worth putting on the record. Not smoking is still the largest factor a person can control for bladder cancer. For how these categories work, see our explainers on what a carcinogen is and hazard versus risk.

• National Toxicology Program, Report on Carcinogens, Fifteenth Edition: 2-Naphthylamine, accessed August 6, 2026
• Occupational Safety and Health Administration, 29 CFR 1910.1003 — 13 Carcinogens (4-Nitrobiphenyl, etc.), accessed August 6, 2026