The best way to protect yourself from germs is to wash your hands with soap for twenty seconds. But how do soapy suds kill infectious bacteria and viruses?
UC Berkeley’s Department of Infectious Diseases and Vaccinology professor Lee Riley, MD, believes soap’s killing power comes from its molecular structure: a chain attached to a long tail. The head of the structure is hydrophilic while the tail is hydrophobic. Some viruses, including Corona virus (the cause of Covid 19), are attracted to the hydrophobic tail. The lipid membrane of these viruses makes them susceptible to the soap molecule’s lipid-piercing tail.
As some pathogens have stable cell walls, they can survive even after the hydrophobic tail of soap penetrates their membranes. But even in these cases, soap molecules can defeat bacteria and viruses by surrounding and isolating them.
Doctor John Swartzberg, a physician and infectious diseases expert at the University of California, Berkeley, explained that when soap attacks these pathogens, its hydrophobic head sticks to the lipid membrane of the cell and its tail sticks to the lipid membrane. Around the pathogen, soap molecules form a small ball called a micelle. As the outer part of the micelles is hydrophilic, bacteria and viruses are easily trapped, resulting in easy hand cleaning.
The effectiveness of soap was evaluated on 20 volunteers who had their hands contaminated with diarrhea-causing bacteria 480 times in 2010. The subjects were then randomly assigned one of three actions: washing their hands with soap, washing their hands with water only, or sitting down. Then, diarrhea-causing microbes were tested on their hands. International Journal of Environmental Research and Public Health published this research.
The bacteria was present in 44 percent of the hands-sitting group. 23% of the subjects in the group that only washed their hands with water had bacteria, while only 8% in the group that washed their hands with soap and water had bacteria.
In Swartzberg’s opinion, soap molecules effectively remove and destroy hand germs. Thus, antibacterial soaps can be unnecessary and even harmful, resulting in antibiotic-resistant bacteria. It is possible to increase antibiotic-resistant bacteria in local water supplies even after washing off antibacterial soap.
Furthermore, antibacterial soap kills all bacteria. Our health depends even on the good bacteria. Time, however, is one of the most important aspects of washing. For the soap molecule’s tail to adhere optimally to pathogens on the hand or other surface, it takes at least 20 seconds. The complete soapy protection is lost when the soap washing time is reduced.