How Does 70% Alcohol-based Hand Sanitizers Kill Microbes ?

Hand sanitizers often contain alcohol such as ethyl alcohol as an active ingredient other ingredients may include water and glycerin. Hand sanitizer has reduced the levels of microorganisms by killing them, just like other disinfectants do. 

  The effectiveness of hand sanitizers depend on quantity used duration of exposure and frequency of use. Usually 70% alcohol-based hand sanitizers, if rubbed thoroughly over finger and hand surfaces for 30 seconds followed by complete air drying can effectively reduce populations of bacteria, fungi and some viruses.

How alcohol-based hand sanitizers kill microorganisms ?

  • Alcohols disturb the normal arrangement of lipids structure of bacterial plasma membrane. The plasma membrane of the bacteria is formed by several phospholipid molecules.
  • Phospholipid is composed of a phosphate group and a lipid. The phosphate group is hydrophilic and the lipid is hydrophobic.
  • The phospholipid bilayer of plasma membrane which is formed by two layers of phospholipids is arranged in such a way that the hydrophilic parts are directly exposed to the internal and external environments of the cell. 

Plasma membrane of microorganisms

  • The reason being is that the internal and external environments of the cell are occupied with water.
  • In most cases the hydrophilic ends are always in contact with water. The hydrophilic nature provides the membrane more stability in the aqueous solutions.
  • When phospholipids come in contact with alcohol, the lipid molecules move out of place and break the arrangement as the hydrophilic ends chase for water. Thus it increases the membrane fluidity.
  • This alcohol stressed condition changes the shape of proteins that are present on the membrane.
  • When the proteins are not in normal shape they cannot perform their routine job. Therefore the microorganisms cannot survive.

Hand sanitizers are commonly used in pharmaceutical companies, hospitals and clean rooms.
Particularly alcohol-based hand sanitizers will be used in combination of water.

Why Alcohol solution with 70% alcohol and 30% of water effectively kills bacteria ?

  • Alcohol in combination of water evaporates slowly, therefore increases the contact time of the sanitizer and thus works effectively.
  • Water acts as a catalyst and plays an important role in denaturing the proteins.
  • The 100% alcohol coagulates the proteins rapidly and forms a protein layer. This will prevent coagulation of other protein molecules. This is the reason why the 70% alcohol is found to be more effective than 100%.