What does short wavelength UV light (UV-C) do?

• A. It can reduce the bacterial load on surfaces
• B. It increases bacterial growth
• C. It mutates DNA
• D. It has no surface effect

Answer: (A)

Short-wavelength UV light, especially UV-C, has powerful germicidal effects. It damages the DNA of microbes by creating thymine dimers, which interfere with replication and transcription. When a microbe can’t replicate, it can’t survive or cause infection, so surfaces exposed to UV-C end up with fewer viable bacteria—i.e., a reduced bacterial load. While DNA damage can sometimes lead to mutations, the practical outcome in disinfection is inactivation and death, not growth. UV-C works best on direct surfaces and won’t sterilize areas that aren’t reached by the light.