The Science of Soap: How Hand Washing Kills Germs

Hand washing with soap and water is a fundamental practice for preventing the spread of infectious diseases. The effectiveness of soap against pathogens like viruses and bacteria is rooted in basic chemistry and physical processes.

Chemistry of Soap

Soap molecules have two distinct ends: one hydrophobic (repels water) and one hydrophilic (attracts water). This structure allows soap to remove dirt and microbes from the skin. When soap comes into contact with water, it forms micelles, with the hydrophobic tails pointing inward and the hydrophilic heads outward, enabling the removal of germs from the skin.

Disrupting Pathogens

Soap's power against germs, including the COVID-19 virus, lies in its ability to disrupt lipid envelopes surrounding some viruses. Soap molecules insert their hydrophobic tails into these lipid layers, prying them apart and inactivating the virus. For bacteria and other microbes, soap helps dislodge them from the skin, trapping them in micelles that are rinsed away with water.

Role of Water

While water alone can flush away some germs, soap enhances water's effectiveness by breaking down oil and grease that bind germs to the skin. This combination ensures a more thorough removal of pathogens.

Practical Application

Regular hand washing is advocated worldwide, including in places like Singapore, where public health campaigns emphasize hygiene to control disease spread. The practice is especially encouraged before eating, after using the restroom, and in public spaces, reflecting its importance in maintaining public health.


The germ-killing power of hand washing comes from the simple, yet effective action of soap disrupting and removing pathogens from the skin. This accessible and effective method remains a cornerstone of public health strategies globally.