Microbiologist: Sometimes 70% Alcohol Kills Germs Better Than 91%. But Why?

We're all concerned about killing anything related to the Corona virus on the surfaces of our home and work. And rightly so. But a microbiologist has explained that sometimes more alcohol content in our sanitizers is LESS helpful for destroying some germs. Seems counterintuitive, right? We want to kill everything with the most firepower, so this doesn't feel true. But it is sometimes.

It's all about dilution... and what you're trying to protect yourself from.

Apartmenttherapy.com talked with microbiologist Dr. Elizabeth Scott, professor of microbiology at Simmons Center for Hygiene and Health in Home and Community at Simmons University in Boston. She explained that alcohol solutions often come in 70% versions and 90 or 91% versions. A 70% alcohol solution has more water mixed with the alcohol than the 91% bottle. For killing some germs, water is a very important part of killing the germ.

For some germs, the 91% alcohol solution is so powerful, it fries the cell membrane before the alcohol can get to the germ inside. But on those same germs, water helps penetrate the membrane, so the alcohol can get inside and complete the mission.

So which percentage is better to kill the flu (or more specifically, the Coronavirus)?


The magic number is anything above 60% alcohol. Any less and it won't help. But anything above 60% will be just fine. That magic number also applies to the common cold, HIV, and the flu. On the other hand, if you're trying to attack a "norovirus" (not Corona), no amount of alcohol works.

If you're spraying your kitchen counters to stop salmonella or E Coli, go with a 70% solution. But for a surface that might have a virus lingering on it, go above 60% or higher, or higher, or higher.

The article goes on to say that washing your hands thoroughly (20 seconds of good ol' scrubbin') rids you physically of every type or virus and bacteria from your hands. Do that and all the other basic hygiene practices to try and stay healthy.