Ever wonder why disinfectants kill 99.9% or 99.99% of germs, but never promise to kill all germs?
Surely, in a world where science has achieved amazing things, someone would have invented a 100% effective disinfectant, right?
The answer to this dilemma requires a basic understanding of microbiology and mathematics. A disinfectant is a substance used to destroy or inactivate bacteria, viruses and other microbes on inanimate objects.
There are literally millions of microbes on the surfaces and objects in our household environment. Although most are not harmful (and some are even beneficial), a small percentage of them can make us sick.
Disinfection can include physical interventions such as heat treatments or the use of UV light, but usually we refer to the use of chemicals to eliminate microbes from surfaces.
Chemical disinfectants often contain active ingredients such as alcohols, chlorine compounds or hydrogen peroxide, which attack the vital components of microbes to destroy them.
Why do disinfectants only kill 99.9% of germs?
In recent years, we have become familiar with the concept of exponential growth in the context of the spread of COVID-19 cases. This is a process where the numbers grow at an accelerated rate, which can quickly lead to an explosion in the size of a phenomenon. For example, a colony of 100 bacteria doubling every hour would grow to over 1.5 billion in 24 hours.
In contrast, microbial destruction follows a logarithmic decay pattern, as opposed to exponential growth. In this case, the number of microbes decreases over time, but the rate of destruction becomes slower as the number of microbes decreases.
For example, if disinfectants kill 90% of bacteria every minute, after one minute only 10% of the original number will remain. After the next minute, 10% of that remaining 10% (or 1% of the original number) will still be present, and so on.
Because of this logarithmic decay pattern, it can never be claimed that a disinfectant kills 100% of the microbial population. From a scientific point of view, one can only claim that the reduction of the microbial load has been achieved with a certain percentage of the original population. This is why most household disinfectants indicate that they kill 99.9% of germs, Phys.org explains.
The same logic applies to other products, such as hand sanitizers or antibacterial wet wipes.
Factors influencing the effectiveness of a disinfectant
Several factors influence the effectiveness of a disinfectant in eliminating microbes. The size of the initial microbial population: the more contaminated the surface, the more intensively the disinfectant must act. For example, if a surface only has 100 microbes and you remove 99.9%, it is likely that all the microbes will be gone. But if the original population is in the billions, even a 99.9% reduction can leave millions of microbes.
Exposure time: Heavily contaminated surfaces require longer exposure to the disinfectant for greater effectiveness. That’s why product labels often tell you to leave the solution on for a certain amount of time before wiping the surface.
Environmental factors: temperature, humidity and surface type influence how the disinfectant works.
Resistance of microbes in the real environment: microbes may be more sensitive or resistant to disinfectants outside the laboratory.
The responsible use of disinfectants is essential in reducing exposure to pathogens and, by implication, the risk of illness. Although no disinfectant can guarantee complete destruction of microbes, this does not diminish their importance in infection control. However, their use should be complementary to other measures, such as regular hand washing, to minimize the risk of infection.
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Source: www.descopera.ro
