Soap is a chemical compound made from fatty acids and alkali through saponification. Its unique chemical properties allow it to interact with both water and oily substances, making it effective at removing dirt and grease from surfaces, including skin.
The Science of How Soap Cleans
Soap’s cleaning power comes from its distinct molecular structure. Each soap molecule has two contrasting parts: a hydrophilic, or water-attracting, “head” and a hydrophobic, or water-repelling, “tail”. This hydrophobic tail is also attracted to oils and fats. This dual nature allows soap to act as a bridge between water and substances that do not naturally mix with it, such as oils and dirt.
When soap is introduced to water, the hydrophilic heads orient themselves towards the water, while the hydrophobic tails cluster together to avoid water. When greasy dirt or oil is present, these hydrophobic tails penetrate and attach to the oil and dirt particles. This interaction allows the soap molecules to surround and encapsulate the oil and dirt, a process known as emulsification. The oil and dirt become trapped within tiny spherical structures called micelles.
Inside these micelles, the hydrophobic tails trap the oily grime, while the hydrophilic heads face outward, interacting with the surrounding water. This arrangement allows the otherwise water-insoluble oil and dirt to become suspended in the water. As water rinses over the soapy surface, these micelles, carrying the trapped dirt and oil, are easily washed away. This process effectively lifts and removes grime, leaving the surface clean.
Soap’s Impact on Germs
Soap primarily removes microorganisms, like bacteria and viruses, through physical action rather than destroying them like a disinfectant. When hands are washed with soap and water, soap molecules adhere to oils and dirt on the skin where germs often reside. The emulsification process then lifts these germs along with the dirt into the soapy water.
While soap does not chemically “kill” all germs, it can inactivate certain types of viruses and bacteria. Many viruses, including coronaviruses, are encased in a fatty outer membrane, or lipid envelope. The hydrophobic tails of soap molecules can disrupt and break apart this lipid membrane, effectively inactivating the virus by spilling its genetic contents. This renders the virus unable to infect cells.
The effectiveness of handwashing with soap for germ removal is enhanced by the combination of water and friction. The mechanical action of scrubbing helps to physically dislodge dirt, oils, and the microorganisms clinging to them from the skin’s surface. The water then rinses away the soap, the suspended dirt, and the inactivated or dislodged pathogens. This action makes soap and water a powerful tool for hygiene, even without directly “killing” all germs.