It was discovered in the late 1800s that UVC light can actually be used as a UV light sanitizer with the ability to kill up to 99.9% of germs. The technology was put to use in the early 1900s in Europe for water purification and is still used today.
Without getting too technical, a UVC light sanitizer acts by penetrating the thin wall of a small microscopic organism and destroying its nucleic acids. This disrupts the DNA structure and either kills it or renders it unable to reproduce - and therefore harmless. As a result, the use of UVC light to sanitize and kill germs has many applications.