Electric and/or magnetic fields, static or varying, and electromagnetic waves in general, exist everywhere in various intensities, but the ones that we can perceive with our senses are just a small part.

Out of the entire electromagnetic spectrum (fig.1), extending over 25 orders of magnitude and including waves with several thousand kilometer wave lengths (almost static fields) and waves with lengths in the order of one over a million or one over a billion micrometers (gamma rays, rays from cosmic showers), man can directly perceive only radiations with lengths between 0.4 and 0.9 micrometers (visible light) and only through his eye retina. A little wider band, (infrared rays), following visible light, is revealed by his cutaneous thermic receptors.
This does not exclude the fact that the rest of the spectrum too may stimulate or interfere with the structure and the bioelectric and/or chemico-physical balances of our organism.

Physical interactions and related biological effects are different for various parts of the spectrum and they may introduce temporary or permanent modifications and stimulate specific functions. One of the best known is the "chlorophyl synthesis" in green plants for which UV rays of a specific wave length are needed; they are very similar to those that stimulate the production of the precursors for bone synthesis in man.
In addition we know that every thermic exchange, organic and inorganic, is ruled by infrared ray emission or absorption.

Naturally, stimuli are not always useful and, for our own protection, it is recommended to avoid damaging ones. Very intense exposure provokes serious and evident harmful effects (reddening, burns) which are a good alarm signal. We talk of the Thermic effects on biological tissue when increased friction between water molecules leads to a warming which may induce organic molecular denaturation, as in the case of microwave oven cooking.
The situation is not clear, however, at low "doses", which are insufficient to induce irreversible thermic effects, or other immediate and specific effects (specific damage ). In these cases, it is impossible to exclude disturbances which could increase the incidence rate of pathologies already present in the population due to other causes and not directly recognizable (aspecific damage). Often, the normal statistical fluctuations of such pathologies are vast and so it is difficult to note small increases in their occurence . Furthermore, some of the pathologies are "long term", in that they appear clinically after long delays (up to several decades) from the initial event and often they require successive stimuli to initiate the pathologic process. This explains the great difficulties in demonstrating the effects experimentally. It must be added that, for very low doses, living organisms can defend themselves thanks to their homeostatic capability. This refers to their ability to recognise, repair or eliminate small "disorders", preventing possible harm from them, as happens for several noxious agents..... Naturally, this ability has individual limits and may depend also on living conditions.

As far as "radiation quality" is concerned, (i.e. its physical characteristics), a close investigation into electromagnetic waves has brought to light a strange effect known as wave-corpuscle dualism, according to which a wave may be considered as being made of many corpuscles, called photons. At low frequencies, the  undulatory aspect of radiation dominates, while at very high frequencies the corpuscular one predominates. Photons with energies higher than 10  eV, are "corpuscles" potentially able to ionise the water molecule (the most common molecule in living organisms) at room temperature; this explains why they are classified  as ionising radiations. In practice, therefore, the vast electromagnetic radiation spectrum is divided into two sectors: IR, ionising radiations, and NIR, non-ionising radiations. IR behave similarly to electron, proton, or neutron beams, and their physical chemical and biological effects have been widely investigated especially because of the great impact of the atomic bomb and radioactive fall-out from nuclear atmospheric experiments, and for the increasing nuclear utilizations in the industrial field, but, most of all, for the medical uses of radiation. Ionising radiations may be carcinogenic, but they also represent the best and most succesful weapon in treating all kinds of tumours and neoplasias, especially those which are surgically unreachable.

Electrosmog refers only to the NIR sector.