How does UV light disinfect things and what all can it disinfect?
In: Chemistry
Ultraviolet light is higher energy than visible like and can react with living tissue. The same thing that can make a human skin cell become cancerous can scramble a pathogen’s DNA to the point it can no longer function.
Some pathogens are more resistant to UV light than others, but the specific kind of UV used as a disinfectant is UV-C, which is even higher energy than what causes sunburns. It will kill most anything that is exposed to it, but exposure is the key. It isn’t going to do much for pathogens hiding under dirt.
Some lifeforms aren’t built to withstand that spectrum of light so it literally scrambles their DNA.
UV radiation is ionising. That means that if it collides with certain molecules, it ionises them – puts them into a reactive state. If UV radiation ionises DNA, the DNA has a pretty high chance of changing its pattern as a result of that. Since the pattern of DNA is vital for its function, a change in the pattern can cause all sorts of problems, depending on where the change is and what the new pattern does. UV light isn’t extremely penetrating, so the worst it does to humans a thick block of cells) is kill and mutate the outermost layers (the skin), but bacteria are just individual cells forming a thin sheen across a surface. Expose a bacterium to enough UV radiation and its DNA will mutate enough that the bits vital for life stop working, and the bacterium dies.
Certain frequencies of UV light are ionizing, meaning that when the light particles (photons) hit atoms, then can cause the atom to break any atomic bonds it has to other atoms.
The ionizing effect of the UV light destroys the chemical machinery of bacteria and causes it to die. It also damages the DNA or RNA of viruses which will render them inert.
UV light has very little ability to penetrate matter, so it will only ionize a very thin layer on the outside of the object exposed. This is perfect for sterilizing objects which may have a thin layer of bacteria or viruses on the outside such as your cellphone.
Because the UV is unable to penetrate very far into solids, it is fairly safe to be exposed to, since most of the radiation is absorbed by the dead outer layer of skin, and not the living parts of your body. You should still avoid being exposed to a UV sterilizer light, as it can damage your eyes fairly quickly, and can also cause damage to the skin if you are exposed for a long time.
The sun puts out the same UV frequencies, so sunlight can also perform the same sterilization as a UV lamp. The amount of sunlight required to sterilize and object will vary depending on the location, time of year, time of day, and the cloud cover. Also, since the object has to be left outdoors and unprotected by any covering, it is possible that it will be re-contaminated by things in the environment even as the original microbes are sterilized.
Not all UV light is ionizing. The UV light put out by regular black-lights such as those used at parties is non-ionizing and harmless. Only specialized lamps putting out higher energy UV can be used for sterilization.
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