Hand sanitizer can be especially convenient for killing germs when you’re on the go or traveling. But while many hand sanitizers claim to kill 99.9% of germs, they’re not effective against everything — including some common bugs that can make you sick.
“The claim for 99.9% effectiveness is based on laboratory tests … under ideal conditions” and against specific germs, said Dr. Anthony K. Leung, a staff physician at Cleveland Clinic specializing in infectious diseases. “Many factors can affect the effectiveness, [such as] visibly dirty or greasy hands, [an] … insufficient amount of hand sanitizer and low alcohol concentration.”
Plus, there are certain kinds of bacteria, viruses and parasites that are actually resistant to hand sanitizer.
We talked to experts about when hand sanitizer isn’t effective and why, tips on how to properly use it, and when to opt for hand-washing instead.
First of all, how does hand sanitizer work exactly?
The main active ingredient in alcohol-based handrubs is either isopropanol or ethanol, explained Jason Tetro, a microbiologist and author of “The Germ Code.” When either of these “comes into contact with the proteins of a bacterium or a virus … [it] causes a significant amount of harm that can lead them to no longer function.”
In other words, the alcohol changes or breaks down the germs and doesn’t let them infect.
What kind of germs are resistant to hand sanitizer — and why?
Hand sanitizer is ineffective against certain types of pathogens because of how they are structured.
This includes some common viruses, such as norovirus (the highly contagious stomach bug) and adenovirus and rhinovirus (both cause cold symptoms), Leung said. But why?
They don’t have an “envelope” (an outer layer of lipids/fats that many viruses have). This outer layer can be disrupted by alcohol, which causes them not to work, Tetro explained. But when viruses are non-enveloped, the alcohol has a harder time getting into the virus, and “it gets repelled.”
For bacteria, certain types “can form spores, which protect [them] in harsh environments,” Leung added.
Think of spores like a tank, Tetro said. The inside of the bacterium is protected by this strong material on the outside.
“Alcohol may do some damage, but simply will not break through all the layers,” he explained.
Clostridium difficile (which causes the colon to be infected and severe diarrhea) is an example of this kind of bacterium that can survive against hand sanitizer, according to Mayo Clinic.
Lastly, some parasites that have a “tough outer shell” are also resistant to alcohol, Leung said.
For instance, cryptosporidium, which is the leading cause of waterborne illness in the U.S., has a cell wall-like a “bomb shelter” that “fully protects the inside structure,” Tetro explained. Using alcohol “would be like throwing a ping pong ball at it.”
So when should you opt for hand-washing instead of using hand sanitizer?
Hand-washing is always preferred when possible, according to Dr. Soniya Gandhi, associate chief medical officer at Cedars-Sinai Medical Center. But it’s important to use “proper technique” for it to actually work.
“Lather [and] scrub [your] hands to create friction … [Scrub] for at least 20 seconds,” Gandhi advised. “Dry [your] hands thoroughly after washing well because wet hands can more easily transmit germs.”
If you don’t have access to soap and water, using hand sanitizer is the next best option, she said. Here’s how to use it properly to maximize effectiveness:
- Make sure it contains at least 60% alcohol. “These higher concentration sanitizers are more effective at killing germs than those with lower alcohol concentrations,” Gandhi explained.
- Squeeze the appropriate amount of sanitizer on your hands. “Use enough … to keep the hands wet for 15-20 seconds while you’re rubbing,” Tetro said.
- Thoroughly rub it into both of your hands. “Not just [on] the palms but [also] in-between the fingers,” Leung added.
- Do not wipe off the sanitizer. Let it dry on your hands, Gandhi said.
Just remember that hand sanitizer doesn’t work against all germs. Leung especially recommends washing your hands with soap and water after using the bathroom, before eating and preparing food, after handling garbage, and after coughing or sneezing into your hands. Also, handrubs aren’t effective at removing harmful chemicals or when your hands are visibly dirty or greasy.
Don’t forget about these other simple ways to avoid sickness.
These tips can provide an added layer of protection from getting infected by germs, including those that are alcohol-resistant:
- When your hands aren’t clean, avoid touching your face. “Surfaces such as [your] eyes and mouth have mucous membranes and easily serve as port[s] of entry” for germs, Leung said.
- Regularly clean and disinfect high-touch surfaces, like door handles and light switches, according to the Centers for Disease Control and Prevention. When someone is sick, use a bleach solution or EPA-registered disinfectant product.
- “If there are clothes [or] laundry that are soiled with vomit [or] feces, wash items with detergent and hot water at the maximum available cycle length and dry at the highest heat setting,” Gandhi recommended.
- Avoid preparing or handling food for others if you’re sick, she said. Wait at least 48 hours after your symptoms are gone.
Lastly, don’t underestimate the power of washing your hands. It’s the “gold standard of eliminating germs” and “the most powerful tool we have to … prevent … getting sick,” Gandhi said.