Because the detection of micro-organisms was mainly linked with diseases, humankind had the idea that all micro-organisms are dangerous. Besides the search for resources to fight the diseases (antibiotics), more attention was also given to our hygiene and our environment. Therefore, products were designed to clean and disinfect.

There is an important difference between cleaning and disinfection, as well as between surfaces and our bodies.

Cleaning: The removal of dirt on a surface (material or our skin). This is done with soaps (or detergents).

Disinfection: To make a surface free of micro-organisms by eliminating them. This is performed with biocides (or disinfectants).

Soaps and chemical biocides are fully chemical in composition, wherein the biocides contain an active substance which is bactericidal. Nowadays, soaps and biocides are sometimes combined with a product that should do both the cleaning and the killing (eg Dettol). The ultimate goal of cleaning and disinfection is to ensure that no micro-organisms and their food source (= dirt) remain present anymore.

The resistance problem:

The use of detergents and disinfectants initially appeared to work well and you could quite easily make a surface free of dirt and micro-organisms. However, because of their long time on earth, microorganisms learned quickly to adapt to changing circumstances.

Over several decades after the introduction of disinfectants, the micro-organisms found ways to circumvent this threat, which today we call resistance. This is to say that the micro-organisms become increasingly aware on how to survive an attack of disinfectants. The efficiency of disinfectants is therefore diminished.

Also in terms of cleaning, there is a growing problem. One of the mechanisms used by the micro-organisms to defend themselves against these chemical attacks is through the formation of increasingly persistent biofilms. This ensures that cleaning agents (soaps, detergents) are no longer able to remove the dirt on surfaces, because the dirt is often trapped in biofilms that are almost impermeable to soaps.

The disinfection paradox:

However, there is a greater danger lurking behind chemical cleaning and disinfection. The impact on the microbial dynamics is the creation of harmful microflora.

What happens with chemical cleaning and disinfection:

If we take as an example again, a surface where food, moisture and space is available to keep a microbial community of 100 micro-organisms alive. Immediately after disinfection, the micro-organism count will have fallen sharply.

(Total 100: 12 good, 4 bad, 84 empty)

In fact, because of the resistance, a number of micro-organisms will survive disinfection. A disinfectant has no aftereffect, so after a few minutes the survivors will begin to regrow. They now suddenly have a lot of space (the vacant spots of eliminated microorganisms), a lot of food (the eliminated(dead) micro-organisms themselves serve as a food source) and moisture (come with the disinfectants).

Since resistant harmful germs can survive a disinfection attack, and therefore regrow much faster any disinfection will result in a microbial community that contains more and more resistant harmful germs. Again, this new microbial community will stabilize itself using a safety margin to Ensure that they do not occupy all the places so they can survive as long as possible.

After a number of disinfections the new microbial community that has even more harmful microbes will look like the following diagram:

(Total 100: 22 good, 38 bad, 40 empty))

For clarification we compare the diagram of the natural microflora  to the diagram showing the microflora after disinfection :

Natural microflora:

(Total 100: 42 good, 18 bad, 40 empty))

Microflora after disinfection

(Total 100: 22 good, 38 bad, 40 empty)

Both surfaces still have the same quantity of micro-organisms but the total number of harmful microbes is, because of the resistance problems, much higher when disinfection protocols are used.

As we use more disinfection, more harmful microbes are found. This is the disinfection paradox.