WASHINGTON — The government issued warnings on Friday about two materials used daily by millions of Americans, saying that one causes cancer and the other might.

Government scientists listed formaldehyde as a carcinogen, and said it is found in worrisome quantities in plywood, particle board, mortuaries and hair salons. They also said that styrene, which is used in boats, bathtubs and in disposable foam plastic cups and plates, may cause cancer but is generally found in such low levels in consumer products that risks are low.

Frequent and intense exposures in manufacturing plants are far more worrisome than the intermittent contact that most consumers have, but government scientists said that consumers should still avoid contact with formaldehyde and styrene along with six other chemicals that were added Friday to the government’s official Report on Carcinogens. Its release was delayed for years because of intense lobbying from the chemical industry, which disputed its findings.

John Bucher, associate director of the National Toxicology Program, which produced the report, said evidence of formaldehyde’s carcinogenicity was far stronger than for styrene and that consumers were more likely to be exposed to potentially dangerous quantities of formaldehyde.