Extensive research has been conducted into possible health effects of exposure to electromagnetic fields, including many types of radio signals. The WHO states that the scientific knowledge in this area is now more extensive than for most chemicals. The consensus of many expert reviews by independent public health agencies is that there are no established health hazards from exposure below the international recommendations. In May 2011 radiofrequency (RF) electromagnetic fields were classified as possibly carcinogenic to humans (Group 2B), a category used when a causal association is considered credible, but when chance, bias or confounding cannot be ruled out with reasonable confidence. The WHO has identified areas for continuing research to support future health risk assessments. Information on new research publications is available from the EMF-PORTAL.