How’s that saying go again? The one about exposing something to sunlight in order to sterilize it? It’s absolutely true on the microscopic level. When exposed to a sufficient amount of sunlight, microbes will die, often violently. A microbe is a microscopic organism, meaning we literally cannot see it without a microscope of some kind or other.
Our Sun radiates light in a spectrum, only a small part of which is visible to us. Another small part is infrared (IR) light, which although we can’t see IR we can feel it as heat. The other small part is ultraviolet (UV) light. We can’t see or feel UV light but other species, including many birds and insects, can see it. However, UV light does cause damage to our skin and eyes as you all know, so we do feel it, but only after it’s too late to prevent a sunburn.
Science has known for some time that UV light sterilizes surfaces by killing harmful bacteria. The terminal effect of UV is called phototoxicity. The arrival of powerful microscopes has made it possible to watch microbes die in real time. Conveniently, modern microscopes may have an optional built-in UV light. This tool is useful in highlighting specific parts of an organism, but if the UV light is left focused on the specimen for too long (more than a few seconds) the microbe will explode and spill its internal organs. The excellent video below explains the ins and outs of death by UV light, while providing several high resolution examples.
We humans live a long time, primarily because most of us manage to avoid unnatural death. This leads to the perception that life is hardy (as in, hard to kill). Paradoxically, life is robust and simultaneously very fragile and vulnerable. Life is endlessly fascinating.
“Why Do Microbes Explode Under UV Light?” (10:58)