How UV light kills microbes

Viruses don’t reproduce on their own, but they do have genetic material, either DNA or RNA. They reproduce by attaching to cells and injecting their DNA. Some viruses burst out of the infected cell (this form of reproduction is called the lytic cycle), while others merge into the infected cell, reproducing every time that cell divides (lysogenic).

If you’ve ever gotten a sunburn, you’ve had a taste of how UV light kills viruses: UV light can damage DNA. A DNA molecule is made of two strands bound together by four bases, adenine (A), cytosine (C), guanine (G), and thymine (T). These bases are like an alphabet, and their sequence forms instructions for cells to reproduce.

UV light can cause thymine bases to fuse together, scrambling the DNA sequence and essentially throwing a wrench into the machinery. Since the DNA sequence is no longer correct, it can no longer replicate properly. This is how UV light annihilates viruses, by destroying their ability to reproduce.