7 Common Objects You Should Never Leave in a Hot Car

As summer temperatures soar, the inside of a parked car can turn into a furnace—easily exceeding 130°F—posing serious risks to anything left inside. Beyond the obvious hazards like spoiled food or theft-prone electronics, several everyday items can become dangerous or damaged when exposed to extreme heat. Here’s what you need to know to avoid costly mistakes and potential safety hazards this season.

**Aerosol cans** are a ticking time bomb in hot cars. The Ideal Gas Law explains why: as temperatures rise, the pressure inside sealed cans increases proportionally. A can of hairspray or spray paint left on a dashboard can explode with enough force to shatter a windshield, as evidenced by real incidents—including a 2017 case in Washington State where a hairspray can blasted through a car’s windshield. In the UK, a man suffered serious injuries when a spray paint can exploded in his van, requiring surgery. Most aerosol cans carry warnings to avoid temperatures above 120°F, but car interiors can easily surpass that threshold. Store them in a cool, shaded place instead.

**Medications** are another critical concern. Heat can degrade their effectiveness, turning life-saving drugs into useless—or even harmful—substances. Aspirin breaks down under extreme conditions, while hormone-based medications lose potency. Liquid medications dry out, gel capsules melt, and some antibiotics, like tetracyclines, can cause kidney damage when chemically altered. Even common drugs like insulin are temperature-sensitive, failing to work properly if exposed to heat above 86°F. A study by Poland’s Medical University of Lodz tested EpiPens stored in different car locations: after just half a day, those in the trunk degraded by 3.3%, those in the cabin by 13.3%, and those in the glovebox by 14.3%. Trunks and gloveboxes are among the worst places to store meds.

**Electronics**—smartphones, laptops, tablets, smartwatches, and earbuds—suffer in high heat. Apple and Samsung both warn that their devices operate best between 32°F and 95°F. Exceeding these temperatures can cause overheating, leading to throttled performance, frozen apps, dimmed screens, or even permanent damage. Apple advises storing devices between -4°F and 113°F. If your phone or laptop overheats, power it down and move it to a cooler environment immediately.

**Batteries** of all kinds—from AA cells to lithium-ion power banks—are also at risk. Heat accelerates degradation, causing batteries to lose capacity, leak, or rupture. Energizer explicitly advises travelers to carry batteries in cabin luggage rather than checked bags due to fire risks. Panasonic echoes this warning, recommending against leaving batteries in hot cars where temperatures can spike dangerously.

**Plastic water bottles** might seem harmless, but they’re not. When heated, plastic can leach chemicals like antimony and bisphenol A (BPA) into the water, turning a refreshing drink into a potential health hazard. The FDA warns that prolonged exposure to high heat can degrade the plastic, making it unsafe for consumption.

**Alcohol-based products**—including beer, wine, and hand sanitizer—are another red flag. Heat can cause pressure buildup in sealed containers, risking explosions or leaks. Hand sanitizer, in particular, is highly flammable and can ignite if exposed to high temperatures.

**Pets** should never be left in a hot car, period. Even with windows cracked, temperatures inside a vehicle can become lethal within minutes, leading to heatstroke or death. Many regions have laws against this practice, with severe penalties for offenders.

The bottom line: extreme heat transforms a car into a hazardous environment for a surprising number of everyday items. Whether it’s a can of hairspray, a bottle of insulin, or your smartphone, check your backseat and trunk before locking up. When in doubt, take it with you.