Do antibacterial coatings really offer what they promise?

Even if the Covid 19-pandemic is carried by a virus, it has also resulted in a growing popularity of antibacterial coatings. But does that make sense? Reinhard Berghofer-Guem and Mario Bortolotti from Adler Werk Lackfabrik answer this question in their guest article.

The corona pandemic has brought much more attention to antibacterial and antiviral coatings. Whether such coatings are worth the effort can be questioned. Image source: Ines Meier -

Since the coronavirus pandemic at the latest, antibacterial coatings have been met with lively interest. In the meantime, there are a wide variety of products with an antibacterial finish: from floors to furniture in kitchens, bathrooms and children’s rooms, these coatings are supposed to protect us from invisible dangers.

Bacteria are omnipresent: more than 150 species of bacteria colonise the palm of the human hand alone. This scientifically proven statement could be used in a vociferous way to promote antibacterial coatings.

Antibacterial coatings not always the right choice

That is why we at Adler have decided against developing and manufacturing antibacterial furniture coatings. And not without reason. For example, the vast majority of bacteria do not cause diseases. Some strains even hinder the spread of other pathogens.

In addition, a coating against bacteria is usually not effective against viruses. The same applies to other pathogens such as fungi or parasites. The virus SARS-CoV-2 as the trigger of COVID-19 cannot be dealt with in this way.

Considerable obstacles for antibacterial coatings

Products with antibacterial properties are subject to the European Biocidal Products Regulation 528/2012 and are therefore subject to authorisation. At Adler, we only reach into the box of biocidal additives when it is unavoidable for functional reasons, e.g. in wood preservatives. In the case of coatings used indoors and in the home, particularly thorough consideration is required as to whether the use of biocidally active substances is justified. For a strong effect of antibacterial coatings – ideally up to a “disinfection” of the surface by killing pathogens – an extremely high concentration of biocides is required, which would be in a medically questionable range.

The frequently advertised nano-silver is also considered an environmental toxin, which even when added in very small quantities – i.e. in large dilutions – triggers the label “Harmful to aquatic organisms, with long-term effects” in the product’s safety data sheet. Do we really want these substances in our living environment, especially after it has been proven that nanoparticles are deposited in the human body?

Misleading information

Some coatings advertise a confirmed antibacterial effect of 99.9 %. This suggests high effectiveness. However, this value is also often achieved by paint surfaces without biocide treatment. The reason for this is the low-structure, smooth surface and the cross-linking density that modern paint films have. This means that bacteria have no basis for rapid cell division on clean painted surfaces.

If furniture is coated with antibacterial lacquers, this can lull the consumer into a false sense of security and tempt him or her to stop taking hygiene and cleanliness so seriously, which are vital to maintaining good health.

It must also be remembered that in hospitals, medical practices and other medical facilities, the use of antibacterial coatings does not eliminate the need for regular surface disinfection according to the established hygiene plans, as the disinfection must be effective against a wide range of different pathogens: bactericidal, tuberculocidal, levurocidal and virucidal.

No shortage of innovations

In recent years, there have been numerous innovations in the development of paint systems. In particular, due to the availability of new raw materials, a wide variety of coatings with additional properties have come onto the market: Coatings with anti-fingerprint properties, self-healing coatings or pigment paints with very high ring indentation resistance.

It makes perfect sense in the search for new sales opportunities to also position niche products for special areas of application on the market. Before developing a corresponding product, however, it is always necessary to clarify the advantages, the application possibilities and areas of use and, above all, to ask the question of the necessity, even the meaningfulness, of such a functional coating.

Currently, furniture varnish systems with antibacterial properties are in greater demand. We discussed this issue intensively at Adler and ultimately decided not to launch any antibacterial furniture varnishes on the market. We forgo the use of environmental toxins in favour of a product with very limited benefits. This is because coatings made of high-quality furniture varnishes already without an antibacterial finish do not offer bacteria a breeding ground for multiplication.


What are pathogens?

Pathogens are substances or organisms that cause harmful processes in other organisms. In medicine, this property is referred to as “pathogenicity”. Pathogens can be bacteria, viruses, fungi, parasites or prions.

By definition, antibacterial substances only act against one group of pathogens – bacteria. They are not effective against viruses and other pathogens, and only to a limited extent against fungi.

What types of pathogens are there?

Viruses are the smallest pathogens. They consist only of genetic material (DNA or RNA), which is surrounded by a protective protein shell. The virus attaches itself to a cell, penetrates it and thus introduces its genetic material into the host cell’s genetic material, forcing it to produce new viruses. Viruses do not have a metabolism and are therefore unable to reproduce themselves. Examples of virus-related diseases are measles, influenza, coronavirus infections, mumps, chicken pox, hepatitis, rubella, herpes and HIV.

Prions (proteinaceous infectious particles) are proteins that can be present in the human or animal organism in both normal (physiological) and abnormal and then pathogenic structures. They do not contain DNA. The danger posed by pathogenic prions is that they are able to transform physiological, non-pathogenic prions into pathogenic ones. Examples of prion-related diseases: Creutzfeldt-Jakob disease, BSE (mad cow disease).

Fungi are chlorophyll-free plants, there are about 200,000 species worldwide.

A distinction is made between so-called “macromycetes”, which are edible / poisonous mushrooms, and “micromycetes”, which are microscopically small species of other origin. Mushrooms can cause allergies in sensitive people. Furthermore, certain fungi (moulds) form toxic metabolic products (mycotoxins). Foodstuffs affected by this can cause poisoning. In indoor air, they can cause respiratory diseases and even asthma.

Bacteria are microorganisms that consist of a single cell. Unlike viruses, bacteria can reproduce by dividing and then growing again into independent bacteria. Examples of bacteria-related diseases include urinary tract infections, scarlet fever, heart muscle inflammations, meningitis (meningitis), etc.

What is disinfection or sterilisation?

Disinfection is the killing of pathogenic (disease-causing) agents or germs. A distinction is made between hand disinfection, surface disinfection, equipment disinfection, etc.

Sterilisation is the killing of all germs (including those that do not cause disease). This is common practice in the medical field in the form of equipment sterilisation.

In the clinical sector, disinfection plans are defined to prevent the spread of diseases. These disinfection plans are based on requirement values depending on the expected risk of infection. Ongoing disinfection is carried out several times a day; the disinfectants to be used are noted in so-called disinfectant lists. The use of antibacterial coatings in the clinical field does not replace ongoing disinfection.

How do antibacterial coatings work?

Bacteria can reproduce by dividing and then growing again into independent bacteria. Antibacterial coatings usually intervene in this function: Due to the special nature of antibacterial coatings, bacteria are prevented from growing or important transport systems for supplying the cell with bacteria are prevented from functioning. This happens, for example, through the co-use of nanoscale silver ions. Silver has a bactericidal effect (effective against bacteria) in its finely dispersed form.

When silver is used in the coating, minute doses of silver ions are released over a very long time. This “silver” blocks enzymes and prevents their vital transport functions in the bacterial cell, impairs cell structural strength and damages the bacterial surface. This gives the coating an “antibacterial” effect.

Silver ions also have a limited effect against fungi. The fungal growth of some types of mould is inhibited, but the fungi are not killed.

Where are antibacterial coatings used?

Antibacterial coatings are used in a wide variety of fields – some of which have been in use for many years.

In the medical field – e.g. for catheters or other medical “indwelling products” – antibacterial “surface treatments” have been used successfully for a long time.

Another field of application for antibacterial films are interior coatings, e.g. of food storage containers (plastic containers). The use of nanosilver is controversial, and it is now banned in interior refrigerator coatings.

In the private sector, however, the antibacterial surface treatment of furniture, tabletops, furnishings, etc. has hardly proven itself. On the one hand, the need is limited by only conditional and delayed effectiveness against bacteria; on the other hand, the effect against other types of pathogens such as viruses is lacking, with the result that infections are not prevented in a variety of diseases.

From today’s point of view, possible areas of application for antibacterial coatings are moderately stressed, publicly accessible and heavily frequented areas such as homes for the elderly, kindergartens or schools. Whether the coating actually offers any benefit here – or in the private sphere – remains to be seen.

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