Alcohol-based hand sanitizers work by killing microbes that may be on the hands, such as bacteria, viruses and fungi, typically by dissolving the cellular membrane. Alcohol kills bacteria primarily by denaturing proteins and dissolving the lipid membrane.
Proteins are the building blocks of cells, and in order to function properly, proteins must be dissolved in water. In alcohol, the proteins in cells are not able to function properly and become denatured. Alcohol also breaks down the bonds between the hydrophobic fatty acids that form the outer lipid layer of bacterial cells. With no membrane to hold together the components of a bacterial cell, it breaks apart and is no longer able to function as a unit.
The U.S. Food and Drug Administration recommends hand sanitizers with a 60 to 95 percent concentration of alcohol to kill most microbes present on the hands. However, even alcohol-based hand sanitizers within this range are unable to kill certain kinds of germs. Alcohol also evaporates quickly after killing the first layer of microbes on the skin, leaving enough behind to quickly re-colonize. Hand sanitizers do not function as a substitute for hand washing, as they do not necessarily remove dirt, which may contain other organic materials such as feces or blood.