Can You Leave Hand Sanitizer in a Hot Car?

Alcohol-based hand sanitizer can help lower the risk of getting Covid-19 and other infectious diseases when handwashing with soap and water is not an option. That’s why many people leave hand sanitizer in their cars—so they always have it on hand for trips to the gas station, grocery store, or just about anywhere.

However, when a Facebook post went viral suggesting that hand sanitizer might explode in a hot car, it seemed like yet another thing to worry about. In fact, this scenario is highly, highly unlikely, experts say.

Hand sanitizer does contain ethyl alcohol, which can evaporate at room temperature into an ignitable vapor, and is considered a flammable liquid. However, there is not enough volume in a small bottle of hand sanitizer to create such a flammable mixture, says Guy Colonna, senior director of engineering standards for the National Fire Protection Association.

“When a liquid like hand sanitizer reaches a ‘flash point’ it can produce vapors which could ignite—but those vapors still need to be met with an ignition source to catch fire,” he explains.

This flash point is 63 degrees F, adds Jack Caravanos, DrPH, clinical professor, NYU’s College of Global Public Health, New York City. “If you put this gel in a shallow cup and the temperature of the alcohol gel and room air was 63 F and above, then lighting a match slightly above the liquid would cause it to flame up,” he says.

The lowest temperature at which alcohol-based hand sanitizer spontaneously ignites is 685 F, he adds. “If the interior of your car got to 685 F, then this liquid would spontaneously ignite. That scenario is impossible, and chances are other parts of the car would auto-ignite first.”

Even this theoretical risk can be lessened even further by storing your sanitizer in a cool, dark place in your car such as the glove compartment, Caravanos says.

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Hot weather and hand sanitizer: Other concerns

While leaving your hand sanitizer in a hot car likely won’t cause it to catch fire or explode, it may lose some of its effectiveness in the heat. This is why the Food and Drug Administration (FDA) cautions against storing hand sanitizer at temperatures above 105 F.

Hand sanitizers that are in a hot car without air-conditioning may rapidly lose potency because the active ingredient, alcohol, begins to evaporate at warm temperatures, says Nwadiuto Esiobu, PhD, professor of microbiology and biotechnology at Florida Atlantic University. “I usually keep mine in the pigeonhole (cubby hole) of the car, which is often cooler and shaded.” (Just a public service announcement: Hand sanitizer doesn’t last as long as you think it does.)

On the flip side, cold weather could cause your hand sanitizer to thicken, Caravanos adds. “The minute it hits your hands it will warm up,” he says.

Temperature aside, alcohol-based hand sanitizers can be toxic if ingested, and hand sanitizers with the wrong ingredient can be deadly. The FDA has been cracking down on hand sanitizer products that are labeled to contain ethanol or ethyl alcohol, but have actually tested positive for methanol or 1-propanol, both of which can be toxic when absorbed through the skin or ingested. The FDA now keeps a running list of hand sanitizers to avoid.

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