Have you seen that sensational viral social media post about how storing plastic bottles of hand sanitizer in your car might be a fire hazard come summer?
The Western Lakes Fire District's Facebook post said, "While infrequent, there have been cases in the recent past where reflecting light placed through a clear bottle was able to focus onto a combustible surface and cause a fire. This has primarily been through water bottles, but since hand sanitizer is often stored in the same vessel we wanted to pass it along for your safety. The principle is identical and obviously an additional issue would occur if it happened in the presence of an alcohol-based product."
They have since clarified that "our message quickly became misconstrued" into something along the lines of what we presume is your hand sanitizer is bound to explode like a mini bomb in your car. (Psst...that's not going to happen.)
The National Fire Prevention Association (NFPA) said that, yes, hand sanitizer is alcohol-based, which means it is flammable near open flames. But in response to this viral post, Guy Colonna, the NFPA's director of technical services, explained that the temperature of your car would have to be 700° F or more to spontaneously ignite. Sounds pretty hellish...and pretty impossible.
Now that hot topic is settled, this whole discussion made us curious. Okay, a bottle of hand sanitizer stored in my car is not going to explode, but will it still be as effective?
According to CDC hand hygiene experts we spoke to, the WHO formula for homemade hand sanitizer, which has been used globally in Kenya and Central America for COVID-19, has been tested and proven to have a shelf life of 19 months. It maintains its alcohol concentrations for that time even in hot conditions. (Although they do also recommend storing in a cool, dry place, when possible.)
"Hand sanitizer has a shelf life. Even in ideal conditions, some of the alcohol will evaporate over time. Heat speeds this up," explains Jill Grimes, MD, a board-certified family physician in Austin, Texas and the author of The Ultimate College Student Health Handbook: Your Guide for Everything from Hangovers to Homesickness. "Think about when you cook something on the stove. The alcohol evaporates and decreases the concentration of alcohol remaining. Similarly, hand sanitizer can lose effectiveness when it gets hot."
As the alcohol begins to evaporate, the concentration of alcohol—the portion of the sanitizer that deactivates germs—decreases.
So how hot does your car really get in the midday sun? Grimes points to a study published in the journal Pediatrics that found, on average, a 40° F increase—most of which happens in the first 30 minutes after you flip off the AC.
It's also important to keep an eye on its best-by date, says Sheena Malik, MD, a family medicine physician in Los Angeles, California.
"Keep an eye on the expiration date, as the alcohol content in the sanitizer gradually drops as it gets closer to that time," she says. For best results, refresh your hand sanitizer if it's past its prime date, and "store in cooler locations or places that will avoid direct sunlight or repeated heat exposure. Your purse, gym bag or a shelf at home," will do the trick, Malik adds. In other words, tuck that bottle in your bag or pocket to use when you're in the car, then bring it back inside rather than storing it in your cup holder or glove compartment.
Beyond storing it correctly, a lot of the effectiveness of sanitizer lies in, well, your hands.
"The biggest issue with hand sanitizer is still what I call the 'splash and dash:' grabbing some and rubbing for 5 seconds doesn't cut it. You need a full 20 seconds rubbing your hands with sanitizer, just like washing in the sink with soap and water," Grimes says. "Be sure to get all the areas of your hands. The tips of the fingers and the thumbs are missed most often."