Why 100 percent alcohol doesn't kills bacteria?

Answer 1

Probably because 100% alcohol is very flammable, truly an explosion hazard, hard to keep from evaporating, and lower concentrations will do the job.

The alcohols used in the medical disinfection role are about 70% of either ethyl alcohol, iso-propyl alcohol, or maybe a mixture. Also known as "rubbing alcohol". Its VERY poisonous, not only to bacteria. Used for wiping needles medical instruments, etc as a fast way of sterilizing. Some combination of alcholols are delivered in evaporating gels to make a hand wipe that visitors to hospitals can use.

Also disinfecting is "de-natured" or industrial alcohol, which is a mixture of ethanol with 10% methanol, and almost no water. The industrial type is stained purple, and includes a foul tasting disinfectant emetic to discourage drinking it (because methanol is toxic causing blindness, insanity and death). The lab type is clear, smells of vodka, and is just as toxic! It will sterilize medical equipment.

Answer 2

100 percent alcohol is less effective at killing bacteria than say 70 to 80 percent because 100 percent alcohol evaporates to fast to kill bacteria. One way alcohol kills bacterial cells in by damaging (denaturing) proteins in their cell walls and membranes.

Some water is required in order to prevent the alcohol from evaporating too quickly allowing some bacteria to be killed. Therefore, alcohol with a 10 to 30 percent water content will be more effective at killing bacteria than pure alcohol.

Answer 3

It is, on household surfaces. However, in the human body, alcohol cannot achieve enough of a concentration in the bloodstream to treat bacterial diseases. (Yes, even if you were chronically intoxicated, this still wouldn't work! In addition, there would be serious consequences of chronic intoxication/Alcoholism.)

Also, alcohol does not sterilize a surface. It is similar to using a broom to sweep the dirt away. When an alcohol prep pad is used for venipuncture, starting an IV or even any injection, the proper use of one is to swab the area starting from the center and working in a circular motion in an outward spiral. This merely "Sweeps away" the bacteria or germs that are present but does not sterilize the surface, meaning kill the bacteria, including the skin. Betadine is used thereafter as a sterilizer, or at least should be.