Antibacterial effect of alcohol

The antibacterial properties of alcohol are well known. Nowadays, there is a growing interest – how to make antibacterial cosmetics, gels and soaps at home, the composition of which would contain alcohol. We suggest what to look out for and how to prepare a solution with the right concentration of alcohol.

Would 90%-100% alcohol be best for home antibacterial preparations? No – 70% alcohol is optimal.

Why the best bactericidal concentration is around 70% alcohol?

An alcohol concentration of 60-80% effectively destroys the cell wall of bacteria by denaturing their proteins. In other words, it shears the fibres of their protein, changes its structure and renders the protein biologically inactive. Such an alcohol solution is effective against most bacteria, fungi and some viruses. Alcohol in this concentration will penetrate the bacterial membrane, i.e. the wall of the bacteria, into its interior. Protein denaruration – this is irreversible damage to proteins. It also occurs through the action of heat, heavy metal salts or concentrated acids. Such damage deprives the protein of its biological function.

Why does 100% alcohol not kill bacteria?

If, on the other hand, you use 100% alcohol, the affected bacteria will be ‘sealed’ and survive. When you use pure alcohol on a single-celled bacterial organism – the alcohol will pass through the cell wall of the bacteria and begin the process of coagulating the protein directly in that cell wall. The ring of coagulated protein will then stop the alcohol from penetrating further into the cell. The cell, which would have received a kind of “warning” – would become temporarily inactive, but not dead. If the danger had passed, the bacterial cell would begin to function again. Protein coagulation – otherwise known as protein desquamation – involves the clustering of protein (colloid) particles into larger assemblies. This process is then called the transition of the sol into a gel (coagulation). It is a reversible process because the entire protein structure is not damaged.

Other contraindications for the use of pure alcohol in antibacterial cosmetics:

• Alcohol in concentrations of 90%-100% will evaporate more quickly, i.e. it is less persistent.
• A 70% alcohol solution has a safer flammability level. However, remember that it is also flammable. That is, in a room where large areas have been sprayed with an alcohol-based solution, you cannot smoke cigarettes or use lighters.

Types of alcohol

The most common, with the greatest economic importance, are methanol and ethanol. We use methanol as:

• • solvent (fats, resins and varnishes are dissolved in it)
  • fuel
  • in the chemical industry
  • in the pharmaceutical industry

Ethanol is most commonly used as:

• propellant
• in the food industry
• in the pharmaceutical industry