As a microbiologist with extensive experience in the study of germs and their interaction with various substances, I can provide a comprehensive answer to your question about the effectiveness of hot water and soap in killing germs.

Firstly, it's important to recognize that germs encompass a broad spectrum of microorganisms, including bacteria, viruses, and fungi. The efficacy of hot water and soap in eliminating these microorganisms can vary significantly based on the type of germ and the specific conditions in which they are exposed to these substances.

Hot Water: The temperature of the water plays a crucial role in its germicidal properties. Generally, water that is hot enough to cause a sensation of heat to the human touch, typically around 40-49 degrees Celsius (104-120 degrees Fahrenheit), can be effective in reducing the number of bacteria on surfaces. However, to truly kill a wide range of germs, water needs to be much hotter. Boiling water, which reaches 100 degrees Celsius (212 degrees Fahrenheit), is known to kill most types of bacteria and viruses. This is because high temperatures can denature proteins and disrupt the cell walls of microorganisms, leading to their inactivation.

Soap: Soap, on the other hand, is a surfactant that works through a different mechanism. It is capable of lifting dirt, grease, and microbes from surfaces and skin. The process of soap working against germs is primarily through mechanical action—physically removing them from surfaces rather than killing them. However, some soaps contain added antimicrobial agents that can kill or inhibit the growth of bacteria. The FDA has noted that plain soap can be just as effective as antibacterial soaps for everyday cleaning, and the overuse of antibacterial agents may contribute to antibiotic resistance.

The Vanderbilt study mentioned suggests that cold water can be just as effective as hot water in certain contexts. This could be due to the mechanical action of washing with soap and water, which is a critical component of germ removal regardless of the water temperature. The act of scrubbing and rinsing helps to physically dislodge and wash away germs.

In conclusion, both hot water and soap have their roles in germ removal and control. Hot water is more effective at higher temperatures and can kill a broader spectrum of microorganisms, while soap, through its surfactant properties and potential antimicrobial additives, is effective at physically removing germs from surfaces and skin. The combination of both, particularly with proper handwashing techniques, is the most effective way to prevent the spread of germs and maintain hygiene.

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Cold water works just as well as hot water, says a Vanderbilt study. Plain old soap is just as effective as antibacterial, says the FDA. ... We're taught the basics as young kids: Use hot water to help kill germs and bacteria.Dec 17, 2013read more >>