Abstract:

The energy of electromagnetic radiation is derived from the fusion in the sun of four hydrogen nuclei to form a helium nucleus. The sun radiates energy representing the entire electromagnetic spectrum. Light is a form of electromagnetic radiation: All electromagnetic radiation has wave characteristics and travels at the same speed (c: speed of light). But radiations differ in wavelength (λ). Light energy is transmitted not in a continuum stream but only in individual units or photons: E = h clλ. Short wave light is more energetic than photons of light of longer wavelength. Ultraviolet radiations (UV) (λs200-400 nm) can be classified in UVA (λs 315 - 400 nm.); UVB (λs 280 - 315 nm) and UVC (λs < 280 nm). UVB and UVC are the most significant UV radiations to induce biological responses. Electromagnetic radiations on molecular oxygen lead to several reactive products known as Reactive Oxygen Species (ROS). High O2 content in biological systems promotes ROS synthesis. If ROS are not controlled by endogenous antioxidants, cell redox status is affected and tissue damage is produced ("oxidative stress"). ROS induce lipid peroxidation, protein cross-linking, enzyme inhibition, loss of integrity and function of plasmatic and mitochondrial membranes conducing to inflammation, aging, carcinogenesis and cell death. While infra-red radiations lead to noticeable tissue temperature conducing to severe burns, UVA and UVB undercover react with skin chromophores producing photochemical alterations involved in cellular aging and cancer induction. As UV radiations can reach cellular nucleus, DNA can be damage. Human beings need protection from the damaging sunbeams. This is a very important concern of public health. While humans need to protect their skin with appropriate clothing and/or by use of skin sunblocks of broad spectrum, some bacteria that are extensively exposed to sunlight have developed genomic evolution (plasmid-encoded DNA repair system) which confer protection from the damaging effect of UV radiation.