Why is 70% alcohol solution a much better disinfectant than a 90% alcohol concentration? Wouldn’t a higher concentration mean better?

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Why is 70% alcohol solution a much better disinfectant than a 90% alcohol concentration? Wouldn’t a higher concentration mean better?

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23 Answers

Anonymous 0 Comments

So many smart explanations. For dummy dums like me…due to water content it hangs around a bit longer so the alcohol can actually work it’s magic

Anonymous 0 Comments

It’s all about fire hazard vs evaporation rate vs protein disintegration.

70% is the most suitable condition. Additionally, if you use about 90% alcohol- proteins will denature real fast and make a protective outer layer which will effectively decrease the efficiency.

Anonymous 0 Comments

Simply put, water is required for the denaturization of proteins, which is how isopropyl alcohol works as a disinfectant.

Back in microbiology we used alcohol in various concentrations to disinfect surfaces, and then cultured
Them in petrie dishes. The 70% had the least growth.

Perhaps someone with a chemistry background could explain how this works.

Anonymous 0 Comments

90 & 99% evaporates far too fast. It’s very well suited for use on cleaning electronics, not disinfecting.

Anonymous 0 Comments

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.

Anonymous 0 Comments

Alcohol is like Hulk who beats up bad guys. And water is the vehicle Hulk uses to reach thebad guys.

With 90% alcohol and 10%water, alcohol can’t reach the bacteria to beat them up. But 70%alcohol and 30% water can reach all the bacteria

Anonymous 0 Comments

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.

Anonymous 0 Comments

90% alcohol evaporates quicker than 70% alcohol, so the 70% alcohol is able to stay on the bacteria longer and attack it more

Anonymous 0 Comments

90% evaporates too quickly to be as effective – it will still disinfect, just not as completely. The 70% stuff takes a bit longer to evaporate, so longer exposure time means more time to do its job and therefore more effective.

Anonymous 0 Comments

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.