HOUSTON, July 29 — Tanning beds have moved to the highest-risk cancer category of radiation sources in an update from the International Agency for Research on Cancer (IARC).

Citing evidence from case-control studies and a meta-analysis, the IARC monograph working group “raised the classification of the use of UV-emitting tanning devices to Group 1, ‘carcinogenic to humans,’ ” the authors reported in the August issue of The Lancet Oncology.

In a meta-analysis published in 2006, the IARC working group concluded that people who begin using tanning devices before age 30 have a 75% greater risk of cutaneous melanoma than the general population (Int J Cancer 2006; 120:1116-22).

The working group also cited case-control studies showing “consistent evidence of an association between the use of UV-emitting tanning devices and ocular melanoma.”

The IARC reclassified all forms of ultraviolet radiation as a single carcinogenic entity. Historically, mutations caused by exposure solar radiation had been attributed to UVB. However, the same mutation was identified in UVA-induced skin tumors in mice.

UVA, UVB, and UVC previously had been classified individually as “probably carcinogenic to humans” (group 2A in the IARC system). In the updated report, the IARC moved UV radiation as a whole into the highest-risk category, eliminating distinctions between UVA, UVB, and UVC.

With regard to other sources, the IARC working group found insufficient evidence to conclude that welders face an increased risk of UV radiation-induced ocular melanoma. However, the group said, “a full review of the carcinogenic hazards of welding will be undertaken with high priority.”

The working group also classified all forms of ionizing radiation as group 1. Forms of radiation affected by the action included radon, plutonium, radium, phosphorus-32, and radioiodines.

Working group member Nicholas Priest is an employee of Atomic Energy of Canada. Co-author Ron Mitchel is a consultant to Atomic Energy of Canada. Co-author Colin Muirhead disclosed a financial relationship with the UK Ministry of Defense. Co-author J. Hall disclosed a financial relationship with Electricite de France. Co-author A. Green disclosed a relationship with L’Oreal Recherche.