WASHINGTON - The US government on Friday added formaldehyde, a substance found in plastics and other commonly used products, to a list of known carcinogens and warned that the chemical styrene might cause cancer.

In a report prepared for the Secretary of the Department of Health and Human Services (HHS), scientists warned that people with higher exposure to formaldehyde were more at risk for nasopharyngeal cancer, myeloid leukaemia and other cancers.

"There is now sufficient evidence from studies in humans to show that individuals with higher measures of exposure to formaldehyde are at increased risk for certain types of rare cancers ...," the Report on Carcinogens said.

Formaldehyde is a colorless, flammable, strong-smelling chemical widely used to make resins for household items, such as composite wood products, paper product coatings, plastics, synthetic fibers, and textile finishes.

It is also commonly used as a preservative in medical laboratories, mortuaries, and some consumer products, including hair straightening products.

The report, produced by the National Toxicology Program (NTP), also added styrene to the list of substances that were reasonably anticipated to be human carcinogens.

Styrene is a synthetic chemical used in the manufacture of products such as rubber, plastic, insulation, fiberglass, pipes, automobile parts, food containers, and carpet backing.

The greatest exposure to styrene in the general population is through cigarette smoking, the report said.

The American Chemistry Council (ACC), an industry group, lashed out at the report, saying it was concerned that politics may have hijacked the scientific process.

"Today's report by HHS made unfounded classifications of both formaldehyde and styrene and will unnecessarily alarm consumers," Cal Dooley, president and CEO of the ACC, said in a statement.

Jennifer Sass of the National Resources Defense Council, a US environmental group, praised the government for publishing the report in the face of what she described as pressure by chemical companies to prevent its release.

"The chemical industry fought the truth, the science, and the public - but, in the end our government experts came through for us, giving the public accurate information about the health risks from chemicals that are commonly found in our homes, schools, and workplaces," Sass wrote in a blog.

The report also listed aristolochic acids, found in some plants, as a known carcinogen and added the fungicide captafol, some inhalable glass wool fibers, cobalt-tungsten carbide, riddelliine and o-Nitrotoluene to the list of substances reasonably anticipated to be carcinogens.

It, however, said listing the substances did not in itself mean they would cause cancer. Amount and duration of exposure, and susceptibility to a substance were among the many factors that affected whether a person developed cancer, it said.