Over the years, the consensus that harms of antibacterial soaps outweigh their benefits has indeed coalesced. But to understand how antibacterial soaps could harm, we first need to understand how they differ from regular soaps. Also referred to as antimicrobial or antiseptic soaps, they contain chemicals that regular soaps don't.

Many liquid soaps labeled antibacterial contain Triclosan, a synthetic compound, specifically a phenylether or chlorinated bisphenol. While the US FDA classifies it as a Class III drug, i.e., a compound with high solubility and low permeability, Triclosan is also a pesticide. Triclocarban is another common chemical found in antibacterial soaps. Many of the concerns about Triclosan also apply to Triclocarban (1).

Since it appeared on the scene in 1972, Triclosan has steadily permeated through the consumer landscape such that it's practically ubiquitous today (see lists below from 1 and 2).

Triclosan's so ubiquitous it's even found embedded in medical devices such as catheters and sutures to prevent infections (3).

As for its beneficial effect, a 2015 study compared bactericidal effect of plain versus Triclosan-containing soaps in conditions that mimic hand washing, and found no difference in their ability to reduce bacterial numbers during a 20 second exposure (4). In other words, dubious benefit when used for routine hand washing under normal circumstances, i.e., only washing hands for a few seconds. After all, most of us don't scrub as though preparing to do surgery every time we wash our hands.

How Triclosan, A Common Antibacterial Soap Ingredient Inhibits/Kills Microbes

In vitro studies show Triclosan can stop bacteria growing at low concentrations (bacteriostatic), and kill them at high concentrations (bactericidal). It also has some activity against some fungi (5) and even parasites such as those that cause malaria, Plasmodium falciparum, and toxoplasmosis, Toxoplasma gondii (6).

Triclosan is able to target many different types of bacteria by blocking the active site for an enzyme essential for bacterial fatty acid biosynthesis (7, 8). Blocking the enzyme enoyl-acyl carrier protein reductase, Triclosan prevents bacteria from synthesizing fatty acid, which they need for their cell membranes and for reproduction.

Problems With Triclosan

I. Triclosan selects for antibiotic resistance

As widespread Triclosan use increased, labs increasingly started finding cross-resistance to antibiotics. Under selection pressure from Triclosan, bacteria mutate to develop resistance mechanisms to it, which end up bestowing antibiotic resistance as well. In other words, studies show Triclosan selects for antibiotic resistance (see table below from 9).

II. Discharged Widely Into The Environment, Triclosan Can Affect Biomass Such As Algae & Bacterial Communities

Since it's widely used in such a diverse array of products, Triclosan ends up in soil, ground water and municipal wastewater treatment plants. Such plants require proper functioning of microbes to break down sewage. Triclosan can inhibit methane production in wastewater plant anaerobic digesters as well as select for multidrug resistance in such bacterial communities (10). Triclosan's effects persist even beyond because it's discharged from wastewater treatment plants as effluent. Certain algae species in the vicinity of such plants have been found to be very sensitive to Triclosan (11, 12). Triclosan also affects bacterial communities in rivers (13). Potential environmental risk of Triclosan becomes even more relevant in areas of water scarcity where it doesn't get sufficiently diluted.

III. Triclosan Can Alter Gut Microbiota In Fishes & Rodents, Potentially Alter Human Microbiota, & Even Promote Tumors In Rodents

• Triclosan could profoundly (14) and stably (12) alter fish gut microbiota as well as those of baby rats (15).
• While so far Triclosan doesn't appear to affect human gut microbiome, the data are far from conclusive, being based on just one study with 7 volunteers (16). OTOH, a study on nasal secretions from 90 healthy adults found a positive correlation between presence of Triclosan in nasal secretions and nasal colonization by Staphylococcus aureus (17). This suggests Triclosan indeed has the potential to influence, even alter human microbiota.
• One mouse model even found Triclosan capable of promoting liver tumors (18).

IV. Triclosan Can Disrupt Hormonal Function

Triclosan was found to disrupt thyroid hormone-associated gene expression and altered the rate of frog metamorphosis (19). It could also disrupt thyroid (20, 21), estrogen (22), and testosterone (23) function in rats.

V. Triclosan Bans

Given the increasing litany of concerns about Triclosan's deleterious effects on the physiology of a wide variety of species, which may also increasingly include humans, several governments are either considering banning it or have already done so.

• In March 2010, the European Union banned Triclosan from any products that may come into contact with food (2).
• On 16 May, 2014, the US state of Minnesota banned the sale of Triclosan-containing cleaning products (soaps), giving manufacturers time until early 2017 to phase them out (24).
• As of 2015, Health Canada was considering banning Triclosan. It's estimated ~1730 products including cosmetics, health and personal care products containing Triclosan were available in Canada in 2011 (1).
• The US FDA is mulling its regulation (25), with a report due in September 2016.

Bibliography

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2. Alliance for the Prudent Use of Antibiotics. "Triclosan." White Paper prepared by the Alliance for the Prudent Use of Antibiotics (APUA) (2011). http://emerald.tufts.edu/med/apu...

3. Stickler, David James, G. Ll Jones, and Allan Denver Russell. "Control of encrustation and blockage of Foley catheters." The Lancet 361.9367 (2003): 1435-1437. http://carambola.usc.edu/Biofilm...

4. Kim, S. A., et al. "Bactericidal effects of triclosan in soap both in vitro and in vivo." Journal of Antimicrobial Chemotherapy (2015): dkv275.

5. Vischer, W. A., and J. Regös. "Antimicrobial spectrum of Triclosan, a broad-spectrum antimicrobial agent for topical application." Zentralblatt für Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene. Erste Abteilung Originale. Reihe A: Medizinische Mikrobiologie und Parasitologie 226.3 (1974): 376.

6. McLeod, Rima, et al. "Triclosan inhibits the growth of Plasmodium falciparum and Toxoplasma gondii by inhibition of Apicomplexan Fab I." International journal for parasitology 31.2 (2001): 109-113. https://www.researchgate.net/pro...

7. McMurry, Laura M., Margret Oethinger, and Stuart B. Levy. "Triclosan targets lipid synthesis." Nature 394.6693 (1998): 531-532.

8. Levy, Colin W., et al. "Molecular basis of triclosan activity." Nature 398.6726 (1999): 383-384.

9. Schweizer, Herbert P. "Triclosan: a widely used biocide and its link to antibiotics." FEMS microbiology letters 202.1 (2001): 1-7. http://femsle.oxfordjournals.org...

10. McNamara, Patrick J., Timothy M. LaPara, and Paige J. Novak. "The impacts of triclosan on anaerobic community structures, function, and antimicrobial resistance." Environmental science & technology 48.13 (2014): 7393-7400. https://www.researchgate.net/pro...

11. Reiss, Richard, et al. "An ecological risk assessment for triclosan in lotic systems following discharge from wastewater treatment plants in the United States." Environmental Toxicology and Chemistry 21.11 (2002): 2483-2492.

12. Lawrence, J. R., et al. "Resilience and recovery: The effect of triclosan exposure timing during development, on the structure and function of river biofilm communities." Aquatic Toxicology 161 (2015): 253-266. https://www.researchgate.net/pro...

13. Ricart, Marta, et al. "Triclosan persistence through wastewater treatment plants and its potential toxic effects on river biofilms." Aquatic Toxicology 100.4 (2010): http://www.clipmedia.net/galera/...

14. Narrowe, Adrienne B., et al. "Perturbation and restoration of the fathead minnow gut microbiome after low-level triclosan exposure." Microbiome 3.1 (2015): 1. Microbiome

15. Hu, Jianzhong, et al. "Effect of postnatal low-dose exposure to environmental chemicals on the gut microbiome in a rodent model." Microbiome 4.1 (2016): 1. Microbiome

16. Poole, Angela C., et al. "Crossover Control Study of the Effect of Personal Care Products Containing Triclosan on the Microbiome." mSphere 1.3 (2016): e00056-15. http://msphere.asm.org/content/m...

17. Syed, Adnan K., et al. "Triclosan promotes Staphylococcus aureus nasal colonization." MBio 5.2 (2014): e01015-13. Triclosan Promotes Staphylococcus aureus Nasal Colonization

18. Yueh, Mei-Fei, et al. "The commonly used antimicrobial additive triclosan is a liver tumor promoter." Proceedings of the National Academy of Sciences 111.48 (2014): 17200-17205. http://www.pnas.org/content/111/...

19. Veldhoen, Nik, et al. "The bactericidal agent triclosan modulates thyroid hormone-associated gene expression and disrupts postembryonic anuran development." Aquatic Toxicology 80.3 (2006): 217-227. https://www.researchgate.net/pro...

20. Crofton, Kevin M., et al. "Short-term in vivo exposure to the water contaminant triclosan: evidence for disruption of thyroxine." Environmental Toxicology and Pharmacology 24.2 (2007): 194-197. https://www.researchgate.net/pro...

21. Zorrilla, Leah M., et al. "The effects of triclosan on puberty and thyroid hormones in male Wistar rats." Toxicological Sciences 107.1 (2009): 56-64. The Effects of Triclosan on Puberty and Thyroid Hormones in Male Wistar Rats

22. Stoker, Tammy E., Emily K. Gibson, and Leah M. Zorrilla. "Triclosan exposure modulates estrogen-dependent responses in the female wistar rat." Toxicological Sciences (2010): kfq180. Triclosan exposure modulates estrogen-dependent responses in the female Wistar rat

23. Kumar, Vikas, et al. "Alteration of testicular steroidogenesis and histopathology of reproductive system in male rats treated with triclosan." Reproductive Toxicology 27.2 (2009): 177-185.

24. SF 2192 Status in the Senate for the 88th Legislature (2013

25. Kuehn, Bridget M. "FDA pushes makers of antimicrobial soap to prove safety and effectiveness." JAMA 311.3 (2014): 234-234.

https://www.quora.com/Does-anti-bacterial-soap-do-more-harm-than-good/answer/Tirumalai-Kamala