There is a widespread concern that using bar soap is unsafe because pathogenic bacteria from previous use remain on its surface. We decided to check whether such fear is justified.

From use lump soap warn sites hospitals And clinics, as well as municipal resources. Official website of the TV program “Live Healthy” with Elena Malysheva reports: “Bar soap retains microbes that are sources of infection. Moreover, those microbes that live on antibacterial soap are very resistant. Just replacing solid soap with liquid soap reduced the incidence of infections in hospitals tenfold.” The “So Cool” portal, the official resource of the Ministry of Health of the Russian Federation, also warns, that it is better to use liquid soap, since “dirt may remain on the bar.” Health Resources they tell, that “some of the microbes in question found in soap may include bacteria: E. coli, salmonella, and shigella—and viruses, such as norovirus, rotavirus, and staphylococcus. Russian-language Wikipedia in the article “Washing hands” also warns: “Bar soap can retain bacteria on its surface from previous use.”

Bacteria surround us everywhere, they are not only in places that seem polluted to us. Total on the planet there are at least 5*10³⁰ bacteria, their biomass exceeds the total biomass of all animals and plants. Scientists bow down to the fact that in a healthy human body there are even more microorganisms than cells of the body itself. On every square centimeter of skin lives approximately 10 million bacteria. Most of them are not dangerous - they are either non-pathogenic (that is, they do not cause disease, but can, on the contrary, protect the body), or opportunistic (natural inhabitants of the body, they cause diseases only when immunity is reduced). By data US Agency for Healthcare Research and Quality Assessment, less than 1% of all bacteria existing in the world can cause some kind of disease, the rest are useful to the body - they help digest food, kill dangerous microorganisms and are involved in the synthesis of essential vitamins. Microbiologist John Heinz explains: “When you wash your hands, you are not trying to get rid of all the bacteria. "You're just trying to reduce the amount of [dangerous] bacteria to give your immune system a fighting chance."

Specialists from Georgetown University (USA) researched 14 bars of soap, which was used in private homes. The highest numbers of microbes were found on those pieces that were used more often and that remained moist between uses. Those that had time to dry had fewer bacteria. The microorganisms were mainly represented by colonies of opportunistic saprophytic staphylococcus and various families of enterobacteria. Saprophytic staphylococcus most often lives in the genital area and urethra; when immunity is reduced, it causes cystitis and urethritis. And enterobacteria, on the one hand, make up a significant part of the normal intestinal microflora, on the other hand, some representatives of this group, such as E. coli (Escherichia coli), salmonella, Yersinia (plague bacillus) or shigella are dangerous to humans. That is, if we assume that these bars of soap were most often used specifically to clean the skin of the hands after using the restroom, then bacteria living in the urinary tract and intestines logically turned out to be the most common on soap.

Indian scientists decided to study bars of soap no longer in ordinary homes, but in healthcare institutions, namely in 18 dental clinics. All 32 samples they studied contained microorganisms on their surface:

Staphylococcus epidermidis was found in 100% of the samples examined (as the name implies, lives on the skin of people and does not pose any danger if it does not enter the bloodstream of people with weakened immune systems);
87% of the pieces studied contained Klebsiella - the majority of strains include to normal intestinal microflora, some are dangerous and can cause pneumonia, infect the genitourinary tract, vagina, uterus, and also cause acute intestinal infections;
78% had E. coli on their surface (most strains of E. coli harmless, but some can cause severe food poisoning);
56% contained Staphylococcus lemon yellow, another 19% contained Staphylococcus aureus; both types are pathogenic microorganisms and cause dangerous diseases (meningitis, pneumonia, endocarditis and sepsis).

The researchers also discovered two types of fungi, which are primarily dangerous for people with weakened immune systems, as well as two more types of bacteria, one of which is characteristic of the microflora of the colon, and the second of which is characteristic of the surface of the skin.

However, there is no reason to immediately throw away bar soap and buy liquid soap. The authors of both studies only studied what bacteria were on the surface of the soap. Whether they can infect a person who washes their hands with such a piece is another question. The answer to it back in 1988 tried find specialists from the Dial company, a large manufacturer of hygiene products, which presented, among other things, the world's first antibacterial soap. They took a bar of soap, soaked it in water until it softened slightly to simulate the conditions of frequently washing hands with the same bar, and then treated the samples with colonies of two bacteria (Escherichia coli and Pseudomonas aeruginosa) at a concentration 70 times higher than what the scientists found in the samples they actually used. Then 16 volunteers were asked to wash their hands with this contaminated soap. After washing, their brushes were examined for the presence of bacteria - it turned out that even a seriously high concentration did not leave harmful microorganisms on them.

Another earlier study demonstrated similar results. study, conducted by specialists from Procter & Gamble. Instead of Pseudomonas aeruginosa, scientists then used another pathogenic bacterium - Staphylococcus aureus, as well as the already mentioned E. coli. After washing with contaminated soap, no pathogenic bacteria remained on the hands. Elizabeth Ko, senior lecturer of biology at Boston University (USA), explains This is because all pathogenic microorganisms, during the foaming of soap, move from the surface of the bar to the formed foam, and then leave the hands along with it when washed off with water. Tatyana Petukhova, MD, dermatologist at Weill Cornell Medicine and NewYork-Presbyterian Medical Centers, adds: If your immune system is so low that bacteria from your skin can harm your body, then you are more likely to suffer from your own skin flora than to bring something from a bar of soap. Philip Tierno, Clinical Professor of Microbiology and Pathology, summarizes: “Even if several people share a bar of soap, the stars must align perfectly for you to get sick. For example, if you transfer a pathogen from the surface of soap to your hands, but do not wash them thoroughly and rinse off the pathogen, and then immediately eat something with those hands or lick your fingers, then in theory you have a chance of getting sick.” Dermatologist Whitney Bowe comments for National Public Radio confirmed, that in my practice I have never met a single patient who became infected with something from washing their hands with bar soap.

Moreover, bar soap effectively protects not only from bacteria, but also from viruses, showed joint American-Canadian study. The same E. coli was used as test microorganisms, as well as a laboratory-prepared virus that imitates Ebola, but does not cause its symptoms. Scientists invited 18 volunteers, treated their hands with a solution containing pathogens, and then asked them to wash their hands in one of three ways: soap, a disinfectant solution, or chlorine water. Washing hands with soap in terms of removing pathogens from the surface of intact skin showed results comparable to disinfection and rinsing with bleach.

A handwashing guide prepared by experts at the US Centers for Disease Control and Prevention reportsthat both bar and liquid soap are equally effective - it makes no difference which one you use to wash your hands. This assessment confirm and experts from Canada's McGill University, who emphasize that liquid soap causes much more harm to the environment: the carbon footprint of its production is approximately 25% greater than that of bar soap, consumption is usually higher, and it is also usually sold in plastic containers, which are not always recyclable.

So, while many types of bacteria on a bar of soap do remain after use, they are effectively washed away with water after the next user of the bar lathers their hands and creates a lather. Not a single experiment has shown the likelihood of bacteria being transferred to hands from a bar of soap, even pre-treated with a large number of microorganisms.

Cover image: Bild von 422737 auf Pixabay