All disinfectants (bleach, alcohol, ect.) have a “soak time” to be effective at killing viruses and bacteria. This is the amount of time the surface being disinfected has to remain moist and undisturbed to penetrate the cell walls and actually break down the virus or bacteria.
90% alcohol evaporates quickly and does not have the time to fully “soak” into the cells it’s trying to destroy. That’s also why using a single wipe of a bleach wipe doesn’t actually do anything. (Most I’ve seen require enough wipes to keep the surface wet for at least 30 seconds.)
If you’re just removing grime you can see, the concentration doesn’t matter. It’s the microscopic grime that takes time to kill.
The pancake example currently at the top of this thread is perfect!
Absolute alcohol has a very low flash point and it’s easy to accidentally ignite it from a naked flame used to sterilize needles and scalpels, so 70% was considered to be the best compromise. Also it doesn’t evaporate too quickly so when it’s sprayed onto a surface it has sufficient contact time to kill pathogens.
I use 70% alcohol for my mcology hobby. I’ve also used 90% alcohol. The rule of thumb is that things need to soak for three minutes and if you spray it on, 90% evaporates much too quickly. Other than that some are commenting on the mechanism of action where 90% causes cells to coagulate and protect themselves but I don’t know about that. IMHO 90% would work just as well if you reapplied it and waited the three minutes.
Cells are hydrophilic. This means the molecules they are made of attract water. So when the cells come into contact with alcohol mixed with water, the cells will act like a sponge and absorb the water, and also brings with it the alcohol.
If it’s just alcohol, the sponge effect won’t work so well on the cells.
Latest Answers