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Disinfectants And Their Mechanisms Of Action

Let us now go into the case at hand. When we want to disinfect, what do we use and how do we do it? Disinfectants and their mechanisms of action, And, for criteria, why are disinfectants effective, and instead are not harmful?



The best known form of disinfection, available to everyone, is bleach, the common name for sodium hypochlorite , its active compound. This substance is not unknown, since each inhabitant consumes more than 12 liters a year. On the other hand, it is used considerably less. Of course, it is neither supplied nor should it be used in high concentrations.

As little as five parts per million, 5 ppm, kills 99% of microbes in a few minutes, and 500 ppm, which is only 0.05%, kills more than 99.99%, and even the most difficult, spores, also in minutes. Taking into account that, commercially, it is distributed at 5%, a tablespoon in 10 liters of water is enough to have a totally effective dissolution.

Additive and fragrance bleaches work just as well, actually better. One of the additives, polyacrylates, change their surface tension so that the sanitizing solution sticks better to surfaces. On the other hand, adding pleasant fragrances to bleach has been more difficult than you might think, since bleach is known to deactivate most odorous substances.


How does bleach work? Specifically, by oxidizing key proteins of microorganisms , rendering them useless in much the same way as a thermal shock does. Since, like all disinfectants, its action is not specific, we must limit its use to external disinfection. It is true that the tap water has been treated with bleach. But it serves to prevent the accumulation of pathogens in it, and not to attack those inside our body.

There are not a few detractors of bleach, both for its smell and for its ability to attack all forms of life. In addition, it reacts with various residual substances, adding chlorine to their composition. This transformation generates, in some cases, potentially carcinogenic compounds.


So far, everything is true. However, the actual concentrations of these chlorinated compounds are never anywhere near those that are carcinogenic. Therefore, being so far from danger, the advantages far outweigh the disadvantages. Remember that disinfection saves hundreds of millions of lives every year .


Alcohols, Quaternary Salts, and Chlorophenols

Numerous lotions, soaps, shampoos, ointments, pastes, mouthwashes, and other preparations for domestic use, incorporate bactericidal, virucidal, or germicidal agents in general in their formulation.

Disinfection of our hands, which we have to watch so much in these times, is carried out with soap, on the one hand, and with a hydroalcoholic preparation. Both washes deactivate the COVID-19 virus, although the latter to a greater extent.

While with soap we eliminate at most 99% of the germs, the alcoholic solution allows us to reach 99.99%. On the other hand, germicides in toothpaste, or mouthwashes, even kill 99.999% of microbes. This action is leading to the suggestion , very recently, that these preparations can be used as prevention of viral contagion, but it is only an idea under study.


What substances, in particular, have these properties, and how do they act?

Three types of substances, with three different mechanisms of action.

First there are alcohols , of various types. Ethanol, alcohol from alcoholic beverages, isopropyl alcohol, as well as a good number of different alcohols, most of natural origin, are germicidal if the microorganisms are enveloped in fatty material, that is, fatty acids, lipids, or lipoproteins . Alcohols dissolve them, and microorganisms cannot survive this alteration. It is then reasoned that washing hands with alcoholic solution deactivates the SARS – CoV – 2 virus, since it belongs to the viruses that have this fatty envelope.

Second, we have some little-known compounds, the so-called quaternary salts , the most representative compound of which is benzalkonium chloride , better known by its trade name, Zephiran .


Its mode of action will seem curious. They work by puncturing the cell membrane , causing leakage through the puncture. It seems like something very primitive, almost laughable, but at the molecular level this phenomenon is not so simple. The prick I am referring to is produced by chemical affinity, which in turn is based on the similarity between the molecules of the cell membrane, and that of the quaternary salt. The cell becomes confused, allowing some of the quaternary salt to fully insert, creating a pore through which the aqueous medium and vital components of the cell escape .


The third component of this family is made up of chlorophenols . The most common compounds are identified as PCMX and Triclosan , commercial terms that hide a complicated nomenclature. They are found not only in the aforementioned domestic preparations, but also in treatments that confer bactericidal and fungicidal properties to clothes, covers, fabrics in general and other household accessories.


Its action, especially bactericidal and fungicidal, as we have already said, is due to the fact that they deactivate the synthesis of fatty acids in a good number of cells . Specifically, they deactivate a specific protein, which is only used by pathogens and not by the cells of our body. It is, therefore, a fairly selective substance, much more than the previous disinfectants, although it does not reach the selectivity of drugs.

The best known mouthwash is the one named Listerine, in honor of Joseph Lister, the pioneer in antiseptic treatment.  The substance Lister used was phenol, a precursor to chlorophenols.  Instead, today's mouthwashes are a complex mix of alcohols.


So far the most common forms of disinfection. They are not all, of course, and the ones that are could change over time, as research is continually refining, changing and improving the different prescriptions.

Those who follow the media will know that there is controversy over the use of two more agents, such as disinfectants. I am referring to ozone, on the one hand, and ultraviolet radiation lamps, on the other. And I will add hydrogen peroxide, which is not so present in the media, but it does have its supporters.

 Disinfectants And Their Mechanisms Of Action

These substances or devices, as we have already mentioned, can be used as sterilization methods. But they are either dangerous as disinfectants, and their use is discouraged, or they are not effective.

Let's look at ozone first . Indeed, it is a powerful biocide. It reacts with the vast majority of organic substances, and therefore puts the vital molecules of all microorganisms under oxidative stress. But its aggressiveness, and its lack of selectivity, generates significant health problems .

In particular, ozone is a powerful irritant , and it is also so at the concentrations at which it is usually generated in sterilizing devices. In addition, being a gas, its travel is not controllable, and it fills a cabin very quickly.


Furthermore, the use of ozone does not prevent the infection provided by the users themselves, so it must always be used together with other systems in parallel. For example, disinfection of swimming pools with ozone also needs to chlorinate the water, to avoid pathogens contributed by users.

Therefore, as much as popular culture says otherwise, ozone is only good in the stratospheric layer, 23 kilometers above sea level.

With ultraviolet lamps we have two situations. The UV-A or UV-B lamps , which are not germicides and whose use we can cause serious eye problems if used for a long time. On the other hand, UV-C lamps are germicidal , we have already mentioned this. But they are too dangerous, since in a few minutes they can trigger serious damage, due to alteration of cellular DNA. Therefore, they cannot be used as a disinfection system, without evacuating the premises and supervised by professionals. Only professionals!


Finally, the hydrogen peroxide. If you "surf" the net, you will find proponents of a treatment based on consuming, or applying, very dilute solutions of hydrogen peroxide. So far good, because it can do little harm. The funny thing is that, say the defenders, "it serves" to cure all the diseases one can think of. Most of the virtues that his supporters claim are nonsense.

However, there is one case that gave me reasonable doubt. I mean they are claimed to be an effective acne treatment . After all, acne is caused by the growth of bacteria.

Could be. But no. It does not work . When it has been proven, with a good number of individuals, if hydrogen peroxide eliminates acne, the results do not differ from those that do nothing. I mean that the effectiveness of the treatment is the same as the absence of treatment, as it is a condition that the body itself is able to overcome, over time. And it doesn't just happen with acne. For this reason, for a treatment to be approved, it has to show that it is more effective than the natural ability of the human body to heal itself.

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