Isopropyl Alcohol - 70% or Higher?

Isopropyl Alcohol (IPA) disinfects via a process called denaturation. Denaturation breaks down the protein structures of the cell and kills them, neutralizing the bacteria or virus. IPA does not have sporicidal properties, so it is not suitable for sterilization purposes. IPA is mixed with water because water is helps open up the cell membrane allowing the IPA to enter the cell and kill it. A 70% IPA mixture has 30% water by volume.

Because of the key role of water in the antimicrobial process, higher percentages of IPA are less effective. The CDC recommends between 60% and 90%. 70% is commonly available in pharmacies and studies show that for purposes of skin preparation, 70% IPA is optimal. At higher percentages (read less water), the contact time to achieve the same bactericidal effect is significantly longer, oftentimes longer than the evaporation lifetime of the solution, making it ineffective.

Bleach vs. 70% Isopropyl Alcohol: Which Should I Use?

Use Case: Surface Decontamination
Recommendation: Bleach
Aqueous alcohol solutions are not preferred for surface decontamination because of their evaporative nature.

Use Case: Skin Prep
Recommendation: 70% Isopropyl Alcohol
The evaporative nature of rubbing alcohol makes it convenient for skin prep. Bleach is an eye, skin, and respiratory irritant so its use on skin is not recommended.

Sources

Centers for Disease Control and Prevention - Chemical Disinfectants: Guideline for Disinfection and Sterilization in Healthcare Facilities (2008) - https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html

Stanford University: Environmental Health & Safety - Comparing Different Disinfectants - https://ehs.stanford.edu/reference/comparing-different-disinfectants

University of Nebraska, Lincoln: Safe Operating Procedures, Chemical Disinfectants for Biohazardous Materials (Revised 3/21) - https://ehs.unl.edu/sop/s-bio-disinfectants.pdf

United States Environmental Protection Agency (EPA): Selected EPA-Registered Disinfectants - https://www.epa.gov/pesticide-registration/selected-epa-registered-disinfectants

Wikipedia: Denaturation_(biochemistry) - https://en.wikipedia.org/wiki/Denaturation_(biochemistry)

Wikipedia: Isopropyl_alcohol - https://en.wikipedia.org/wiki/Isopropyl_alcohol

Healthline: What to Know About Using Alcohol to Kill Germs - https://www.healthline.com/health/does-alcohol-kill-germs