Where there is no visible light, the heat propagates through an invisible form of light, therefore not by convection (displacement of hot air), nor by conduction (propagation through a solid body). Cells and organs exposed to infrared rays are energetically activated and the increase in temperature determines vasodilation: consequently, blood circulation improves. Thanks to infrared rays, cellular exchanges and the mobilization of metabolic and toxic waste or foreign substances that are deposited in the tissues are optimized.
Electromagnetic radiation with a wavelength between 0.759 μm and 1 mm, ie the portion of the electromagnetic spectrum between the visible and microwaves, is defined as "infrared". Nowadays it is believed that the IR region is divided into 4 sub-regions (near, medium, far, very far IR), to which different measurement techniques are applied: in fact, the IR field covers a spectral region where they are applied for technical detections of both photon counting (near and medium IR) and electromagnetic (very far IR). Infrared radiations are emitted by every 'hot' body and, conversely, if they are absorbed by a body, they give rise to the development of heat; these thermal properties are common to all electromagnetic radiations, but they manifest themselves in a more sensitive way with infrared radiations, which are therefore also called thermal radiations. The infrared emission is linked to transitions between the vibrational energy levels of the molecules.