Hand sanitizer is a convenient alternative to traditional washing, but it is not a full substitute for soap and water. Both methods reduce microbes on the hands, but they achieve this through fundamentally different processes. Understanding the distinct actions of each product reveals why one is the preferred method for overall cleanliness while the other serves as a useful tool for quick disinfection.
The Mechanical Action of Washing with Soap
Washing with soap and water primarily works by physically removing foreign material and microorganisms from the skin’s surface. Soap molecules are amphiphilic, possessing both a water-loving (hydrophilic) head and a water-repelling (hydrophobic) tail. The hydrophobic tails attach to the oils, grease, and fatty layers that hold dirt and germs onto the skin.
As you lather and rub your hands, mechanical friction helps physically dislodge the materials. The soap molecules surround the oils and contaminants, forming tiny spheres called micelles, effectively suspending them. Rinsing with water washes these micelles, along with the trapped dirt and germs, down the drain. This physical removal action makes soap effective at removing all visible foreign matter, not just inactivating germs.
The Chemical Action of Hand Sanitizer
Alcohol-based hand sanitizers work through a chemical process that kills or inactivates microorganisms rather than physically removing them. The active ingredients are ethanol, isopropanol, or n-propanol, and they must be present in concentrations between 60% and 95% to be effective. This high alcohol content acts as an antiseptic, quickly reducing microbial counts on the skin.
The alcohol achieves this by denaturing proteins, disrupting the three-dimensional structure of the proteins that make up the cell walls and protective coatings of bacteria and viruses. This process causes microbes to lose their protective structure, rendering them non-functional and quickly killing them. The presence of water is necessary for this chemical process, which is why concentrations of 60% to 95% are more potent than pure alcohol.
When Sanitizer Fails to Clean
Hand sanitizer’s effectiveness is compromised when organic material like visible dirt, grease, or blood is present. The chemical-killing action of alcohol is inhibited because sanitizer does not physically remove these materials. The dirt can shield germs from the alcohol, making the disinfection process ineffective.
Alcohol is also ineffective against certain hardy pathogens, particularly non-enveloped viruses and spore-forming bacteria. Non-enveloped viruses, such as Norovirus, lack the fatty outer layer that alcohol dissolves, and their protein shell is resistant to denaturation. Bacteria like Clostridioides difficile (C. difficile) form protective spores that alcohol cannot penetrate or kill. In these cases, the physical removal action of soap and water is the only reliable way to reduce infection risk.
Choosing the Right Hand Hygiene Method
Selecting the appropriate method depends on the situation and the condition of your hands. Soap and water should always be the preferred method when hands are visibly dirty or greasy, after using the restroom, and before eating or preparing food. Using soap and water is also necessary when there is known exposure to specific illnesses like Norovirus or C. difficile, due to the physical removal action.
Hand sanitizer is a practical solution for quick disinfection when soap and water are not available. It is most appropriate for use in clean settings where a rapid reduction in common germs is needed. The product must contain a minimum of 60% alcohol to ensure adequate germ-killing power.