Isopropyl alcohol and ethyl alcohol are both types of alcohols used for disinfection, but there are important differences between them. The most significant difference is that no form of isopropyl alcohol is safe to drink, but you can drink purified ethyl alcohol.
Chemical Differences Between Isopropyl Alcohol and Ethyl Alcohol
Isopropyl and ethyl alcohol both have multiple names:
- Isopropyl alcohol: IPA, isopropanol, 2-propanol, propan-2-ol, rubbing alcohol
- Ethyl alcohol: ethanol, grain alcohol
The chemical formula of isopropyl alcohol is CH3CHOHCH3, while the chemical formula of ethyl alcohol is C2H5OH. The -OH functional group that makes both organic compounds alcohols is on the second carbon atom in isopropyl alcohol, but on the end of the molecule in ethyl alcohol.
Both compounds are liquids at room temperature, colorless, flammable, soluble in water, and volatile. But, they have different properties. Isopropyl alcohol has a stronger “medicinal” odor than ethyl alcohol. It has a higher melting point and boiling point than ethanol. Isopropyl alcohol is slightly less viscous than ethyl alcohol and evaporates more quickly. Both compounds irritate skin, but because of how quickly rubbing alcohol evaporates, ethanol is more likely to cause irritation. Both compounds are toxic, but humans have enzymes to detoxify ethyl alcohol, making it reasonably safe to consume.
Difference Between Isopropyl Alcohol and Ethyl Alcohol in Disinfection
For the most part, it really does not matter whether you use isopropyl alcohol or ethyl alcohol for disinfection. Both are highly effective at killing bacteria, viruses, and other pathogens. The two kinds of alcohol vary slightly in their efficacy, compared to each other, mainly depending on their concentration and specific conditions. For example, isopropyl alcohol is more effective at killing FCV (feline calicivirus) at 40% to 60% concentration, while ethyl alcohol is more effective at 70% to 90%.
Neither alcohol is very good as a hand sanitizer when concentration drops to 40%. Both are more effective between 60% and 80% in water than when they are pure. This is because the water in the mixture slows evaporation and allows more contact time with the pathogens. Also, the chemical structure of water enhances the interaction between alcohol and germs.
Isopropyl alcohol is better for disinfecting intact skin in that it is less irritating. However, its toxicity makes it less desirable for disinfecting wounds. For disinfecting surfaces, bleach is better than either type of alcohol because it kills spores that aren’t attacked by alcohol.
Difference Between FCC and USP Alcohol
One of the reasons you can’t drink hand sanitizer, even if it contains ethyl alcohol instead of isopropyl alcohol, is because the alcohol is not pure enough for human consumption. Hand sanitizer, cosmetics, supplements, and pharmaceuticals use USP grade alcohol. While purified, USP ethanol isn’t tested for methanol and heavy metals. This is partly why you’ll hear cases of hand sanitizer containing methanol, a highly toxic alcohol that is absorbed through skin. The other reason, of course, is that some manufacturers intentionally used the chemical.
FCC alcohol is the gold standard of alcohol in terms of safety. FCC grade alcohol is USP grade ethanol that meets additional requirements in terms of heavy metal content. FCC stands for Food Chemical Codex.
The other reason people can’t drink alcohol in hand sanitizer is that ethanol, where used, is denatured. This involves the addition of chemicals that make the alcohol unpalatable and sometimes unsafe for ingestion.
- Centers for Disease Control and Prevention (CDC) (2008). “Guideline for Disinfection and Sterilization in Healthcare Facilities“. Chemical Disinfectants.
- IUPAC (1997). “Alcohols”. Compendium of Chemical Terminology (the “Gold Book”) (2nd ed.). Blackwell Scientific Publications. doi:10.1351/goldbook.A00204
- Multhauf, Robert (1966). The Origins of Chemistry. London.
- Reynolds, S. A.; Levy, F.; Walker, E. S. (2006). “Hand Sanitizer Alert”. Emerg. Infect. Dis. 12(3): 527-529. doi:10.3201/eid1203.050955