Why 70 percent Isopropyl alcohol is preferred hand disinfectant Why not 60 or 80 percent?

Answer 1

as an antiseptic, 70 percent of alcohol is prefered to a stonger solution. Pure alcohol coagulates protein in contact. Suppose the pure alcohol is poured ovr a single celled organism. Th alcohol will penetrate the cell wall of the organism in all direction, coagulating the protein just inside the cell wall. the ring of the coagulated protein would then prevent the alcohol from penetrating farther from the cell, and no more coagulation woul take place. At this time the cell would become dormant butnot dead. under the proper condition the cell would then begin to function. if 70 percent of alcohol is poured to a single celled organism, the diluted alcohol also coagulates the protein, but at a slower rate, so that it penetrates all the way through the cell before coagulation can block it. then all the cell is coagulated and the organism dies.

Answer 2

The percentages refer to the relative amount of alcohol as compared to the amount of water. 70% alcohol is 30% water. 91% alcohol is 9% water. Which is a better disinfectant depends somewhat on how it is used, but 70% alcohol will tend to disinfect much more effectively than 90%+ alcohol. This is particularly true for the disinfection of surfaces, including human skin.

This may seem counter-intuitive, but the reason has to do in part with the fact that alcohol evaporates much more quickly than water. With the 70% solution, evaporation tends to be slower (due to higher water content), and therefore the alcohol will have more time to kill microorganisms. In other words, the 91% solution has a higher tendency to evaporate before all susceptible microorganisms are killed. This is the primary reason that 70% alcohol tends to be a more effective disinfectant for surfaces than 90-91% alcohol.

The 70% solution also helps to ensure that the alcohol enters the cells of microorganisms, rather than just rapidly disrupting the cell walls and doing nothing further, which is what tends to happen with 90%+ alcohol solutions.

Also, the greater relative concentration of water in the 70% alcohol solution means that more proteins--and more types of proteins--in microorganism cells will be denatured (i.e. destroyed). This is because water plays an important role in the destruction of proteins.

This should not be taken to mean that 91% alcohol is not an effective disinfectant; it is. But for maximum efficacy, I would recommend 70% alcohol. If disinfection is a primary concern, you definitely do not want to go above 91%, in any case.

So as we can see, one should not simply see the bigger number and make assumptions based on that.

Answer 3

Seventy percent isopropyl alcohol is the most effective concentration for killing microbes. Lower concentrations are not strong enough, and higher concentrations evaporate too quickly.

Answer 4

Too high of an alcohol content tends to preserve microorgs instead of killing them (or so I've been told, but can't remember the logic behind it).