How UV can cause skin cancer

UV is a physical agent that can cause mutation of our skin. UV from the sun is known to cause cancer as a result of prologed exposure. UV radiation affects the bonds between adjacent pyrimidines located on the same or opposite DNA strands. When this happens, thymine, for example, will bond to thymine forming a T-T dimer called cyclobutyl thymine. Radiation also causes single strand breaks, double strand breaks and various types of DNA base damage.

Single strand breaks are more easily repaired by the intracellular DNA repair mechanism. While when a double strand break, there are three possible outcomes: 1) the molecule will be connected with no errors, 2) the molecule is repaired incorectly and produces a mutated DNA molecule, or 3) the DNA molecule is not repaired. A DNA molecule with a double strand break results in fragmentation of the chromosomes followed by an abnormal distribution of chromosomes during cell division. This is cancer.

Reference:
Kent, C. 1998. Basics of Toxicology. John Wiley & Sons, Inc. New York