toxicity is often non-linear, and many substances that are toxic at very high doses actually have neutral or positive health effects, or are biologically essential, at moderate or low doses. There is some evidence to suggest that this is true for ionizing radiation: normal levels of ionizing radiation may serve to stimulate and regulate the activity of DNA repair mechanisms. High enough levels of any kind of radiation will eventually become lethal, however. Ionizing radiation in certain conditions can damage living organisms, causing cancer or genetic damage. Non-ionizing radiation in certain conditions also can cause damage to living organisms, such as burns. In 2011, the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) released a statement adding radio frequency electromagnetic fields (including microwave and millimeter waves) to their list of things which are possibly carcinogenic to humans. RWTH Aachen University's EMF-Portal web site presents one of the biggest database about the effects of Electromagnetic radiation. As of 12 July 2019 it has 28,547 publications and 6,369 summaries of individual scientific studies on the effects of electromagnetic fields. See also Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) Background radiation, which actually refers to background ionizing radiation Cherenkov radiation Cosmic microwave background radiation, 3 K blackbody radiation that fills the Universe Electromagnetic spectrum FASTRAD Hawking radiation Ionizing radiation Non-ionizing radiation Radiant energy, radiation by a source into the surrounding environment. Radiation damage – adverse effects of ionizing radiation on materials and devices Radiation hardening – making electronics resistant to failure in high ionizing radiation environments Radiation hormesis – ionizing radiation dosage threshold damage theory Radiation poisoning – adverse effects of ionizing radiation on life forms Radiation properties Radiation Protection Convention, 1960 – by International Labour Organization Radioactive contamination Radioactive decay Notes and references External links Health Physics Society Public Education Website Ionizing Radiation and Radon from World Health Organization Q&A: Health effects of radiation exposure, BBC News, 21 July 2011. Physical phenomena