Ah, the 0.1%. Are they monster germs that are immune to everything and are now out for revenge because you just killed their friends? Or are they weak and struggling after just barely surviving a hand sanitizer attack? To understand how and what germs survive hand sanitizer, let’s first look at how hand sanitizers work.
How do hand sanitizers kill germs?
Most hand sanitizers contain alcohol as the active ingredient, whether it be ethanol, isopropyl alcohol (isopropanol), n-propanol, or a combination. These alcohols kill or, in the case of viruses, inactivate germs by making proteins lose their structure, a process called denaturation.1Guideline for Disinfection and Sterilization in Healthcare Facilites, C.f.D.C.a. Prevention, Editor. 2008, Centers for Disease Control and Prevention. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html. Proteins are necessary tools for life. They can fit together like bricks to give bacteria and viruses a protective shell, much like the walls of a house. Germs also use proteins as tools in processes like metabolism (enzymes, for example), getting inside your cells to start an infection, and making more copies of themselves. However, when proteins lose their structure, they become useless. This is why alcohol, at a 60-95% concentration, can work broadly against many types of germs from E. coli to SARS-CoV-2.1Guideline for Disinfection and Sterilization in Healthcare Facilites, C.f.D.C.a. Prevention, Editor. 2008, Centers for Disease Control and Prevention. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html.2Morton, H.E., The relationship of concentration and germicidal efficiency of ethyl alcohol. Ann N Y Acad Sci, 1950. 53(1): p. 191-6. https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-6632.1950.tb31944.x?sid=nlm%3Apubmed3Kratzel, A., et al., Inactivation of Severe Acute Respiratory Syndrome Coronavirus 2 by WHO-Recommended Hand Rub Formulations and Alcohols. Emerging infectious diseases, 2020. 26(7): p. 1592-1595. https://pubmed.ncbi.nlm.nih.gov/32284092
Alcohol sounds really effective. How do any germs survive if they all use proteins? And what germs are they??
There are multiple reasons why alcohol-based hand sanitizers don’t eliminate 100% of germs.
First, alcohols have a difficult time getting through protein-rich materials. For example, viruses that are covered in a protein shell, such as poliovirus and norovirus, are particularly difficult for alcohols to inactivate because the proteins are packed tightly together, which likely helps shield them from the effects of alcohol.4Liu, P., et al., Effectiveness of liquid soap and hand sanitizer against Norwalk virus on contaminated hands. Applied and environmental microbiology, 2010. 76(2): p. 394-399. https://pubmed.ncbi.nlm.nih.gov/199333375Tyler, R., G.A. Ayliffe, and C. Bradley, Virucidal activity of disinfectants: studies with the poliovirus. J Hosp Infect, 1990. 15(4): p. 339-45. https://pubmed.ncbi.nlm.nih.gov/1972949/ Also, when conditions get rough, some bacteria can form endospores, which is similar to a person entering a nuclear fall-out shelter. In this situation, both are extremely well-protected from most threats, including alcohol for bacteria. Clostridium difficile endospores are well known for being essentially immune to the effects of alcohol.6Gold, N.A., T.M. Mirza, and U. Avva, Alcohol Sanitizer, in StatPearls. 2020, Treasure Island (FL): StatPearls: StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK513254/.7Jabbar, U., et al., Effectiveness of alcohol-based hand rubs for removal of Clostridium difficile spores from hands. Infect Control Hosp Epidemiol, 2010. 31(6): p. 565-70. https://pubmed.ncbi.nlm.nih.gov/20429659/
Second, not all alcohols are the same. Each type of alcohol has a different chemical make-up and therefore has slightly different properties that translate to real-world effects. For example, though both ethanol and isopropanol are generally effective against many bacteria and viruses, it is widely recognized that ethanol is more effective against some viruses, while isopropanol is more effective against some bacteria.1Guideline for Disinfection and Sterilization in Healthcare Facilites, C.f.D.C.a. Prevention, Editor. 2008, Centers for Disease Control and Prevention. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html.8McDonnell, G. and A.D. Russell, Antiseptics and disinfectants: activity, action, and resistance. Clinical microbiology reviews, 1999. 12(1): p. 147-179. https://pubmed.ncbi.nlm.nih.gov/9880479
Third, you need to use hand sanitizer properly in order to get the maximal effect. Dirt, grease, and other contaminants on your hands can shield germs from the alcohol, so your hands should be visibly clean before you use hand sanitizer.6Gold, N.A., T.M. Mirza, and U. Avva, Alcohol Sanitizer, in StatPearls. 2020, Treasure Island (FL): StatPearls: StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK513254/. Also, long nails can get in the way. A lot of germs live under fingernails and hand sanitizers usually don’t get under your nails when you rub your hands, especially if your nails are long.9Lin, C.M., et al., A comparison of hand washing techniques to remove Escherichia coli and caliciviruses under natural or artificial fingernails. J Food Prot, 2003. 66(12): p. 2296-301. https://pubmed.ncbi.nlm.nih.gov/14672227/ Lastly, you must use enough hand sanitizer. The FDA recommends using 2.4 mL, which is about half a teaspoon.6Gold, N.A., T.M. Mirza, and U. Avva, Alcohol Sanitizer, in StatPearls. 2020, Treasure Island (FL): StatPearls: StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK513254/. However, one study on healthcare workers found that how much you need to use really depends on the size of your hands. While 2.4 mL is likely enough for someone with small hands, someone with large hands might need to use twice as much to get the same effect!10Bellissimo-Rodrigues, F., et al., Should Alcohol-Based Handrub Use Be Customized to Healthcare Workers’ Hand Size? Infect Control Hosp Epidemiol, 2016. 37(2): p. 219-21. https://pubmed.ncbi.nlm.nih.gov/26598073/ Once you have the proper amount of hand sanitizer in your palm, you need to rub it all over your hands until they are dry, which should take 15-30 seconds.6Gold, N.A., T.M. Mirza, and U. Avva, Alcohol Sanitizer, in StatPearls. 2020, Treasure Island (FL): StatPearls: StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK513254/. At this point, the alcohol is evaporated and most of the germs should be eliminated!
Is the claim about killing 99.9% of germs true then? It sounds like it depends…
The claim is both correct and misleading. Hand sanitizers are regulated and verified by the Food and Drug Administration (FDA), who set the requirement that hand sanitizers kill 99.9% of germs.11Administration, F.a.D., Safety and Effectiveness of Consumer Antiseptics; Topical Antimicrobial Drug Producs for Over-the-Counter Human Use; Proposed Amendment of the Tentative Final Monograph; Reopening of Administrative Record. 2016, Food and Drug Administration. p. 42911-42937. https://www.federalregister.gov/documents/2016/06/30/2016-15410/safety-and-effectiveness-of-consumer-antiseptics-topical-antimicrobial-drug-products-for. So in this sense, the claim is true! However, the FDA only requires companies to show that their hand sanitizers are at least 99.9% effective, in terms of killing, against 18 specific and common types of bacteria known to cause disease.11Administration, F.a.D., Safety and Effectiveness of Consumer Antiseptics; Topical Antimicrobial Drug Producs for Over-the-Counter Human Use; Proposed Amendment of the Tentative Final Monograph; Reopening of Administrative Record. 2016, Food and Drug Administration. p. 42911-42937. https://www.federalregister.gov/documents/2016/06/30/2016-15410/safety-and-effectiveness-of-consumer-antiseptics-topical-antimicrobial-drug-products-for.12Administration, F.a.D., Safety and Effectiveness of Consumer Antiseptic Rubs; Topical Antimicrobial Drug Products for Over-the-Counter Human Use. 2019, Food and Drug Administration. p. 14847-14864. https://www.federalregister.gov/documents/2019/04/12/2019-06791/safety-and-effectiveness-of-consumer-antiseptic-rubs-topical-antimicrobial-drug-products-for. In other words, after using hand sanitizer you should have 1,000x less of these types of bacteria on your hands. However, hand sanitizer is not necessarily this effective on all germs that you are likely to encounter in a day. With 30,000+ bacteria species and thousands of virus species in the world, it is definitely not true that hand sanitizer will kill 99.9% of all of these!
Can we just use 100% alcohol? Won’t that work better than what they sell in the store?
While this sounds like a perfectly logical idea, there are two main reasons why no one sells 100% alcohol hand sanitizers. First, a 100% concentration of alcohol is actually less effective than 60-95% alcohol because alcohol needs water in order to quickly and effectively denature proteins.1Guideline for Disinfection and Sterilization in Healthcare Facilites, C.f.D.C.a. Prevention, Editor. 2008, Centers for Disease Control and Prevention. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html.2Morton, H.E., The relationship of concentration and germicidal efficiency of ethyl alcohol. Ann N Y Acad Sci, 1950. 53(1): p. 191-6. https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-6632.1950.tb31944.x?sid=nlm%3Apubmed Second, your hands would get seriously dried out. Hand sanitizers have ingredients like glycerin or aloe vera to minimize moisture loss. If you used a 100% concentration of alcohol to disinfect your hands, you wouldn’t be able to use it very often, which would defeat the purpose of having it out in common areas of buildings and in health care settings.
Ok, I was really excited about my hand sanitizer, but now I feel worried. Should I be worried?
Rather than worry, recognize the strengths and limitations of hand sanitizers and work around them.
Even though hand sanitizers don’t eliminate 100% of germs, they do greatly reduce the numbers on your hands, thereby significantly lowering your chances of being exposed to enough germs to become sick. However, if you are worried about catching or spreading a particular kind of illness, you may want to check if hand sanitizer is effective for it. For example, hand sanitizer is not effective against norovirus, which is known for causing outbreaks of vomiting and diarrhea on cruise ships and in long-term care facilities.4Liu, P., et al., Effectiveness of liquid soap and hand sanitizer against Norwalk virus on contaminated hands. Applied and environmental microbiology, 2010. 76(2): p. 394-399. https://pubmed.ncbi.nlm.nih.gov/19933337 In fact, one investigation found that long-term care facilities that primarily used hand sanitizers for routine hand hygiene were more likely to have norovirus outbreaks than facilities that primarily used hand washing.13Vogel, L., Hand sanitizers may increase norovirus risk. CMAJ : Canadian Medical Association journal = journal de l’Association medicale canadienne, 2011. 183(12): p. E799-E800. https://pubmed.ncbi.nlm.nih.gov/21844107 Though the association is a bit controversial, the Centers for Disease Control and Prevention (CDC) recommends against using only alcohol-based hand sanitizers to prevent spread of norovirus.14Prevention, C.f.D.C.a. Preventing Norovirus. 11/25/2019 [cited 2020; Available from: https://www.cdc.gov/norovirus/about/prevention.html. As another example, hand sanitizer is not effective against Cryptosporidium, a parasite that causes diarrhea outbreaks in childcare settings.6Gold, N.A., T.M. Mirza, and U. Avva, Alcohol Sanitizer, in StatPearls. 2020, Treasure Island (FL): StatPearls: StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK513254/. If you work in or frequent such a setting where this may be a concern, then be aware that the CDC does not recommend using hand sanitizer to kill Cryptosporidium.15Prevention, C.f.D.C.a. Prevention & Control – Camps. 07/02/2019 [cited 2020; Available from: https://www.cdc.gov/parasites/crypto/camps.html.
If you are worried that hand sanitizer will not do its job in your situation, the solution is simple. Wash your hands with soap and water! The main benefit of soap and water is that soap doesn’t need to kill all the germs on your hands. Soap also works by lifting germs off of skin so that water can wash them away (see our article about hand washing to learn more!). Soap and water hand washing acts against all germs, unlike hand sanitizer, so hand sanitizer is supposed to be reserved for times when washing hands is too inconvenient or not possible.
So in conclusion, hand sanitizer does leave behind germs, but is still a good option if you can’t wash your hands. However, hand washing is always a better choice for ridding your hands of germs.
