The very high-energy UV C light triggers a photochemical reaction. The wavelength of 253.7 nm is absorbed by the cell nucleic acid and, depending on the irradiation dose, leads to the killing or damage of viruses, germs, bacteria and fungal spores. UV C light is therefore used to specifically damage or inactivate micro-organisms (such as bacteria/viruses, yeasts and moulds).

The double helix structure of DNA is based on a purine and pyrmidine base pairing. These are the actual information carriers with the nucleic bases adenine, thymine, guanine and cytosine. The research of the following years showed that the short-wave and high-energy UVC radiation causes a photochemical effect primarily on the thymines. These dimerise, i.e. chain or stick together two information carriers lying next to each other. The molecular change of the bases damages the DNA in such a way that the process of transcription, which is essential for the replication of the DNA and thus also for cell division, can no longer take place. A cell that is sufficiently damaged in this way ultimately dies.