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70% vs 99%: Which Alcohol Is More Effective in Killing Germs and Viruses
# 70% vs 99%: Which Alcohol Is More Effective Against Germs and Viruses?
**Date Posted:** August 2, 2021
While many people believe that higher alcohol percentages equate to better germ-killing power, this isn't necessarily accurate. In reality, both 70% and 99% alcohol have their own unique properties when it comes to disinfection. Let's explore what makes each one effective—or not so effective—in different scenarios.
## Understanding the Difference Between 70% and 99%
When we talk about 99% isopropyl alcohol, we're referring to a nearly pure form of isopropanol. On the other hand, 70% isopropyl alcohol consists of isopropanol diluted with 30% purified water by volume.
Surprisingly, 70% isopropyl alcohol is typically considered sufficient for killing most germs and bacteria. Even the SARS-CoV-2 virus can be effectively neutralized by 70% isopropyl alcohol or 99% isopropyl alcohol diluted to 70%. This suggests that the presence of water plays a critical role in the effectiveness of alcohol-based sanitizers.
## How Does Alcohol Kill Germs and Viruses?
Alcohol works as a disinfectant through a chemical process called denaturation. It targets organisms by breaking down their protein structures and dissolving their lipid membranes. Denaturation disrupts the integrity of the organism's proteins, causing them to lose functionality. Without proper structural support, the organism's cell membrane collapses, leading to dehydration and eventual death.
This mechanism is similar to how soap works when washing your hands. Both alcohol and soap remove pathogens by breaking down their physical barriers. The most commonly used alcohol-based sanitizers are either ethanol (ethyl alcohol) or isopropanol (isopropyl alcohol), with isopropanol often referred to as "rubbing alcohol."
## Why Is 70% Alcohol More Effective Than 99%?
Interestingly, higher alcohol concentrations aren't always better when it comes to disinfection. Alcohols with 99% concentration tend to evaporate too quickly to be fully effective. This rapid evaporation prevents the alcohol from penetrating deep into the cell walls, where it needs to act to kill bacteria. As a result, 99% alcohol isn't ideal for sanitizing hands or surfaces.
Conversely, 70% alcohol strikes the perfect balance between alcohol and water. The addition of water slows down evaporation, giving the alcohol enough time to penetrate cell membranes and destroy the entire organism. This makes 70% alcohol highly effective against many enveloped viruses and bacteria, such as the common cold virus and coronavirus.
However, there are exceptions to this rule. Certain non-enveloped viruses, like norovirus, cannot be eradicated by alcohol at any concentration. In these cases, traditional handwashing remains the most reliable method for eliminating all types of pathogens.
## Real-Life Implications
In practical terms, 70% alcohol-based sanitizers are widely recommended for daily use because they strike a balance between efficacy and usability. They are effective against a broad range of pathogens without being overly harsh on skin. Meanwhile, 99% alcohol might be useful in specific industrial or laboratory settings where quick drying is essential, but it's rarely necessary for everyday cleaning tasks.
It's important to note that no single disinfectant is universally effective against all microbes. A combination of methods—such as regular handwashing, surface cleaning with appropriate agents, and maintaining hygiene practices—provides the best defense against infections.
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**Comments (1):**
*Posted by J Aijqyr on July 22, 2023:*
Great article! I appreciate the detailed explanation about how alcohol works and why 70% is preferred over 99%. Keep up the good work!
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This piece aims to clarify misconceptions surrounding alcohol concentrations and their effectiveness against germs. By understanding the science behind how alcohol works, we can make informed decisions about which products to use in various situations.