Of X rays, viruses, and cooked meat.

The psychology of risk is a tricky business. That's why the American Association of Physicists in Medicine (AAPM) in College Park, Md., worries that many people might react with undue alarm to the Jan. 31 announcement by the government that the National Toxicology Program (NTP) has added ionizing radiation, including X rays and neutrons, to its list of human carcinogens. "It would be a tragedy if patients did not have needed exams because of fears raised by the report," says AAPM Board Chairman G. Donald Frey of the Medical University of South Carolina in Charleston.

To head off such reactions, the NTP's new Report on Carcinogens points out that many of the listed carcinogens, including some drugs, offer society substantial benefits and urges people not to eschew such agents without consulting a doctor or other expert.

Hepatitis B and hepatitis C viruses and some types of the human papillomavirus were also added to the list of known human carcinogens, now totaling 58 agents. The report also notes 188 agents that are "reasonably anticipated" to cause human cancer. New entries in this category include heterocyclic amines, which are chemicals created in overcooked meats (SN: 4/24/99, p. 264), and the heavy metal lead.

The lists aren't meant to be all-inclusive. They ignore compounds to which few people are exposed and those with inconclusive carcinogenicity data.--J.R.