Antimicrobial soap: is it better?

By Iulia Kis

Since the start of the COVID-19 pandemic, thorough hand-washing has been one of the most crucial steps that the population of the whole world had to learn. While the general advice has been to wash hands with soap and water for at least 20 seconds, some people have decided to go above and beyond that advice and use antimicrobial soap. 

The market has quickly responded to the public’s love for the “antimicrobial” label with an increase in cleaning and personal hygiene products that have bactericidal properties. While using these products will definitely ease the user’s mind that they have disinfected their hands well, this instant gratification may not be worth suffering the long term effects of extensive antimicrobial product use.

Both plain and antimicrobial soap work in a very similar way, by disrupting the lipid membranes of cells. One of the most widely used antimicrobial compound that is added to soap is triclosan, a synthetic chlorinated phenol.  It is also used in other products like deodorants, oral hygiene products and has become so widely used that it can routinely be found in human bodily fluids (Adolfsson-Erici et al., 2002). Triclosan has bacteriostatic properties in low concentrations and bactericidal properties in high concentrations (1%)(Kampf & Kramer, 2004). It has different effects in various bacterial strains, but its general mode of action is via disruptions to the cell membrane, cytoskeleton and efflux pumps. 

Even though at a first glance it looks like triclosan would be a great addition to soap, well-performed studies have shown virtually no difference in the efficacy of plain soap and soap with 0.5% triclosan (Gnatta et al., 2013). Both in vitro and in vivo, Kim et al., 2015 found that there was no difference between the efficacy of plain soap and antimicrobial soap containing 0.3% triclosan (maximum concentration considered safe) when used under “real life conditions”. They performed this study by providing subjects with a set of steps required to wash their hands, but there was no time limit. 

A study was performed on a community in New York included 238 families who each had to use either triclosan based soap or normal soap. Symptoms of bacterial or viral infections were observed for 48 weeks (Larson et al., 2004). The results showed that the symptoms were equally prevalent in the two groups, but more community studies need to be conducted before this claim will be considered reliable. 

There are some studies (Fuls et al., 2008) showing that the relative effectiveness of antimicrobial soap compared to plain soap increases when the time and volume of soap is increased, but at this point in time, the literature seems to suggest that there is no real benefit of using antimicrobial soaps on a day-to-day basis. Moreover, it looks like the use of these bactericidal compounds is actually more detrimental, as triclosan especially can cause antibiotic resistance for several bacteria.

It has already been shown that when Pseudomonas aeruginosa was exposed to a 25 mg/L concentration of triclosan, it developed resistance to this compound and cross-resistance to multiple antibiotics, such as tetracycline, trimethoprim and erythromycin (Chuanchuen et al., 2001). This was because the compound caused cells to overexpress the MexCD-OprJ efflux system, which facilitates fast elimination of the administered antibiotics out of the cells.

Besides increasing the quantity of efflux pumps in cells, triclosan promotes antibiotic resistance by increasing antibiotic resistance gene (ARG) transformation (Lu et al., 2020). Gene transformation is a process through which cells take up DNA from other cells through their membrane. This is one of the three processes that can lead to horizontal transfer (the transmission of gene between contemporary bacteria) (Lerminiaux & Cameron, 2019) Triclosan promotes this by increasing both reactive oxygen species production, predisposing the genome to mutations and cell membrane permeability (Lu et al., 2020). Moreover, triclosan exposure at environmental concentrations also enhances the ability of the cells to uptake exogenous DNA. All of these properties result in the possibility of triclosan causing cross-resistance to several antibiotics in both Gram-negative and Gram-positive bacteria. (Lu et al., 2020)

Taking all of the above into consideration, it is no surprise that in recent years more and more antimicrobial products have been reformulated without triclosan. In the US, triclosan has been banned by the FDA for use in soaps, but can still be used in other products, like toothpaste. The European Scientific Committee for Consumer Safety is of the opinion that triclosan (in a concentration of up to 0.3%) is safe to use as there has yet to be evidence of it causing antibiotic resistance in clinical environments. That being said, triclosan is slowly being excluded from the market, as it has gained somewhat of a bad reputation with consumers.

An important point to make is that triclosan is not the only antimicrobial soap ingredient that could have harmful effects, as it has been shown that its alternatives (e.g. triclocarban, benzalkonium chloride, chlorohexidine) can also promote cross-resistance to antibiotics. (Rundle et al., 2019).

So, to shortly answer the question posed in the title: there is very little evidence to suggest that antimicrobial soaps, especially those containing triclosan, are better than plain soap when used by the general public. What is more, they could even have negative long-term effects, like creating antibiotic resistance in other bacteria with clinical significance. 

References:

Adolfsson-Erici, M., Pettersson, M., Parkkonen, J. & Sturve, J. (2002) Triclosan, a commonly used bactericide found in human milk and in the aquatic environment in Sweden. Chemosphere. [Online] 46 (9–10), 1485–1489. Available from: doi:10.1016/S0045-6535(01)00255-7.

Kampf, G. & Kramer, A. (2004) Epidemiologic background of hand hygiene and evaluation of the most important agents for scrubs and rubs. Clinical Microbiology Reviews. [Online]. 17 (4) pp.863–893. Available from: doi:10.1128/CMR.17.4.863-893.2004 [Accessed: 10 March 2021].

Gnatta, J.R., Pinto, F.M.G., Bruna, C.Q. de M., de Souza, R.Q., et al. (2013) Comparação da eficácia antimicrobiana na higienização das mãos: ÓLeo essencial de Melaleuca alternifolia versus. Revista Latino-Americana de Enfermagem. [Online] 21 (6), 1212–1219. Available from: doi:10.1590/0104-1169.2957.2356 [Accessed: 10 March 2021].

Kim, S.A., Moon, H., Lee, K. & Rhee, M.S. (2015) Bactericidal effects of triclosan in soap both in vitro and in vivo. Journal of Antimicrobial Chemotherapy. [Online] 70 (12), dkv275. Available from: doi:10.1093/jac/dkv275 [Accessed: 10 March 2021].

Larson, E.L., Lin, S.X., Gomez-Pichardo, C. & Della-Latta, P. (2004) Effect of Antibacterial Home Cleaning and Handwashing Products on Infectious Disease Symptoms: A Randomized, Double-Blind Trial. Annals of Internal Medicine. [Online] 140 (5). Available from: doi:10.7326/0003-4819-140-5-200403020-00007 [Accessed: 10 March 2021].

Fuls, J.L., Rodgers, N.D., Fischler, G.E., Howard, J.M., et al. (2008) Alternative hand contamination technique to compare the activities of antimicrobial and nonantimicrobial soaps under different test conditions. Applied and Environmental Microbiology. [Online] 74 (12), 3739–3744. Available from: doi:10.1128/AEM.02405-07 [Accessed: 10 March 2021].

Chuanchuen, R., Beinlich, K., Hoang, T.T., Becher, A., et al. (2001) Cross-resistance between triclosan and antibiotics in Pseudomonas aeruginosa is mediated by multidrug efflux pumps: Exposure of a susceptible mutant strain to triclosan selects nfxB mutants overexpressing MexCD-OprJ. Antimicrobial Agents and Chemotherapy. [Online] 45 (2), 428–432. Available from: doi:10.1128/AAC.45.2.428-432.2001 [Accessed: 10 March 2021].

Lu, J., Wang, Y., Zhang, S., Bond, P., et al. (2020) Triclosan at environmental concentrations can enhance the spread of extracellular antibiotic resistance genes through transformation. Science of the Total Environment. [Online] 713, 136621. Available from: doi:10.1016/j.scitotenv.2020.136621.

Lerminiaux, N.A. & Cameron, A.D.S. (2019) Horizontal transfer of antibiotic resistance genes in clinical environments. Canadian Journal of Microbiology. [Online] 65 (1), 34–44. Available from: doi:10.1139/cjm-2018-0275 [Accessed: 10 March 2021].

Rundle, C.W., Hu, S., Presley, C.L. & Dunnick, C.A. (2019) Triclosan and Its Alternatives in Antibacterial Soaps. Dermatitis. [Online] 30 (6), 352–357. Available from: doi:10.1097/DER.0000000000000519 [Accessed: 10 March 2021].