By Aayesha Siddiqui (@aayesha)
Last week I posted about norovius, a common and contagious virus that sends people scurrying for the bathroom. One of the take home lessons was the importance of routinely washing your hands, whether you’re sick or healthy.
But then came the inevitable question: What about hand sanitizers? Won’t they work?
You’ll find wall dispensers full of alcohol-based liquids, gels, and foams outside elevators, in public bathrooms, all around the hospital even. Parents send their kids to school with mini-bottles of the stuff. One of our readers commented, “I keep one in my car to apply after being in public places like stores and supermarkets…thought I was getting rid of the germs.”
Our reader is getting rid of a lot of germs—but not all of them.
The Science Behind the Sanitizer
If you look at the active ingredient on the back label of your hand sanitizer, you’ll most likely find it’s ethyl alcohol (a.k.a. ethanol, the same alcohol that’s in your glass of wine or in your spray of perfume) or isopropyl alcohol (a.k.a. isopropanol, but you probably know it as rubbing alcohol). The bottle should also say that it’s between 60% to 95% alcohol (the concentration that’s most effective in killing off most germs).
So, how does the alcohol actually work? Think of a germ as having a well manicured hair-do. Every strand of hair is styled in a very particular way, and the whole hair-do only works if every strand holds its individual structure. But then the germ steps outside into an especially humid summer day. Its hair-do gets assaulted by the heavy, sticky air; the strands end up going limp, losing their original shape. Goodbye, perfect hair-do.
The germ’s proteins (essential to its life processes) are like its strands of hair, and alcohol is like the humid weather. The alcohol denatures the proteins, causing them to lose their structure, rendering them useless. Goodbye, viable germ.
Why Sanitizer Is Not a Silver Bullet
It sounds like alcohol is pretty powerful, right? Well, there are a few things to consider.
First, consider the pathogen and what kinds of germs are you actually trying to get rid of.
Alcohol-based sanitizers, at the concentrations commercially available, work best against bacteria (like E. coli or salmonella), fungi, and certain types of viruses (enveloped viruses—viruses that have a coat around them, like the influenza virus and HIV). Check, check, and check.
But what about non-enveloped viruses (like norovirus or rotavirus)? Alcohol-based hand sanitizers have been shown to have some effect—with ethanol doing better than isopropanol—but their killing prowess here isn’t as strong as against the other germs. Sanitizers also won’t do much good against protozoa (like what causes malaria) or bacterial spores (like those of C. difficile). (If you want to geek out on the scientific literature, take a look at the World Health Organization Guidelines on Hand Hygiene in Health Care, starting on page 32.)
Take home lesson: It doesn’t hurt to use hand sanitizers, just know that you’re not fully protected.
A key question is: How long will your hands remain free of germs after using the sanitizer?
You rub your hands and the germs start dying off, and the ones that remain even take a bit longer to grow back than usual. Win-win. But that doesn’t mean that the effect persists. You’ll need to re-apply hand sanitizer after you come in contact with a contaminated surface, a sick person, or anything else that might be germ-laden.
Take home lesson: Hand sanitizers are quick-acting, but not long-lasting.
The research that’s been done on the germicidal powers of alcohol has been done both in the lab (in vitro) and in real life with real people (in vivo). These are, of course, two very different settings. Exposing germs to alcohol in the lab is far more uniform than when someone takes a squirt of sanitizer from the hallway dispenser and hurriedly rubs her hands together on her way to wherever she’s going. Or, perhaps her hands are visibly dirty and she doesn’t have time to run to the bathroom—maybe hand sanitizer can act as a stand-in?
The Centers for Disease Control and Prevention caution against this. They emphasize that visibly soiled or dirty hands reduce the efficacy of alcohol-based hand sanitizers. You should therefore wash your hands if there’s anything on them. Using a hand sanitizer can be effective if you have visibly clean hands, but you’ll need to make sure to correctly rub the sanitizer on so it can actually work its magic.
Take home lesson: If you’re going to use sanitizer, make sure your hands are not visibly dirty.
All this talk of sanitizers had me questioning everything I touched. I admit: I too carry a travel-sized bottle in my backpack. I reach for it before I touch public keyboards, after I use public transportation—even sometimes after shaking hands. Am I overreacting? Maybe.
The truth of the matter is alcohol-based sanitizers are useful, convenient, and effective in most circumstances. But they aren’t a cure-all. If you want your bases covered, wash your hands routinely and supplement with alcohol-based sanitizers. And don’t be shy—scrub and rub vigorously. Better safe than sick in the bathroom.