22 Things You Shouldn’t Leave Inside Your Vehicle

While there are certain items that you should keep in your car, there are also some things that should not be left inside. Whether it's due to extreme temperatures, theft or chemical reactions, the interior of a vehicle can be a surprisingly hostile environment for a wide range of everyday objects, such as medication, water bottles and valuables. In addition, you should never leave children and pets unattended in a car, especially on a hot day, or they may suffer heat stroke and possibly die.

Keep reading to get a comprehensive list of things you should never leave in your car.

Key Takeaways Children are especially vulnerable to heatstroke in parked cars as their bodies heat up much faster than adults, increasing the risk at high temperatures. Similarly, you should avoid leaving pets like dogs inside the car because they can quickly overheat. Extreme temperatures can alter the chemical composition of medications, necessitating careful storage as per package instructions to ensure their effectiveness. Visible items like wallets or purses in cars attract thieves, risking financial loss, identity theft and the cumbersome process of replacing personal documents. Important documents are prone to damage and theft in cars, with heat and humidity causing deterioration.

1. Children

While summer driving with the family, the temperature inside a car parked in the scorching sun can put your children at an increased risk of heat stroke if you leave them inside. Heatstroke occurs when the body's temperature rises to dangerous levels. Children's bodies heat up three to five times faster than an adult's, making them more susceptible to the effects of high temperatures.^[1] As a result, you should always bring your children with you even if you’re running a quick errand inside a store.

2. Pets

Like children, pets can quickly become overheated in a car, as the temperature inside can increase dramatically within the span of a half hour, even at relatively moderate outside temperatures.^[2] Dogs in particular, are less efficient at cooling themselves than humans since they rely primarily on panting to regulate their body temperature.^[3]

3. Medications

Many medicines are sensitive to temperature fluctuations and exposure to extreme heat or cold can alter their chemical composition.^[4] Always refer to the storage instructions on your medication packaging and keep medicines in a controlled environment to ensure they remain safe and effective.

4. Wallet or Purse

Thieves often target vehicles for visible items of value and a wallet or purse is a high-value target that can contain cash, credit cards, identification and personal information. If stolen, the contents can be used to make unauthorized purchases, withdraw funds or even steal your identity, leading to long-term financial and legal complications.

The process of canceling cards, securing accounts and recovering from identity theft can be lengthy and stressful. Additionally, replacing personal documents such as your driver's license and social security card can be cumbersome and time-consuming.

5. Important Documents

Documents such as passports, birth certificates, legal papers and financial records contain sensitive information that, if stolen, can be used for identity theft and fraud. The interior of a car can also be an unfriendly environment for paper-based materials where direct sunlight exposure and heat can cause fading and deterioration.

With the exception of your proof of insurance card, you should leave important documents at home.

If you are averse to leaving a physical copy of your proof of insurance in your car, many insurance companies allow you to access an electronic version through their mobile app.

6. Perishable Foods

Leaving perishable food in your car in hot weather can lead to spoilage, foodborne illness and waste. Foods like dairy products, meat, fish and prepared meals can quickly become unsafe to eat when exposed to temperatures above 40°F (4°C) for more than two hours, as bacteria growth accelerates in this temperature range.^[5] In warm weather, the temperature inside a car can reach much higher levels in just a few minutes, dramatically increasing the risk of spoilage.^[2]

Consuming spoiled food can lead to food poisoning, with symptoms ranging from mild discomfort to severe health issues. Moreover, the odors from spoiled food can permeate the interior of your car, creating unpleasant smells that are difficult to eliminate. So, get your groceries inside as soon as possible and definitely remember to bring down those leftover nachos. And if you’re on a road trip, consider opting for drive-throughs and sit-down restaurants instead of perishables.

7. Certain Drinks

Leaving certain drinks in your car, especially for prolonged periods, can affect their quality and safety. Beverages like milk, juice or even some carbonated drinks can spoil or ferment when exposed to high temperatures, leading to unpleasant tastes, odors and potential foodborne illnesses if consumed.

Wine can be particularly problematic, as the heat can accelerate the aging process, causing wine to "cook," which flattens its flavors and aroma, making it taste dull and lifeless. Similarly, cold temperatures can cause the liquid to freeze and expand, potentially pushing out the cork or cracking the bottle.

8. Water Bottles

When exposed to high temperatures, potentially harmful chemicals from plastic water bottles, such as bisphenol A (BPA), can leach into the water.^[6] Also, water bottles that have already been opened and left in the heat, can grow bacteria.

9. Batteries

High temperatures can cause the chemicals inside batteries to expand, potentially leading to leakage of corrosive liquids that can damage electronic devices and car interiors. Cold temperatures, on the other hand, can reduce a battery's effectiveness and lifespan by slowing down the chemical reactions necessary for power generation.

Furthermore, the leakage from batteries not only poses a risk to electronic devices but also represents a significant environmental hazard, as the chemicals can be harmful if they come into contact with skin or are ingested. To prevent these risks, it's advisable to store batteries in a temperature-controlled environment and avoid leaving them in your car for extended periods.

10. Lighters

If you leave a lighter in a hot car, you could expose yourself and your vehicle to dangerous situations due to the flammable liquids contained within the lighter. When exposed to high temperatures, the fluid inside a lighter can expand, increasing internal pressure. This can cause the lighter to leak flammable liquid or gas, posing a risk of fire or injury.

11. Electronics

Leaving electronics in your car, especially under extreme temperatures, can lead to irreversible damage.^[4] The internal components of electronic devices, such as smartphones, laptops and tablets, are sensitive to temperature changes and exposure to high heat can shorten their lifespans. Battery parts can even melt together or warp. Conversely, cold temperatures can freeze the liquid crystal displays (LCDs) and reduce battery life.

12. Luggage

Luggage often contains valuables such as clothing, personal items, electronics and sometimes travel documents or cash, which are attractive to thieves looking for an easy score. A break-in can result in the loss of not only expensive items but also irreplaceable personal belongings and sensitive information. Furthermore, the absence of these items can significantly disrupt travel plans, leading to additional expenses and complications, especially if travel documents are taken.

13. Jewelry

Cars are not secure storage spaces and visible jewelry can attract thieves, leading to the loss of valuable and often sentimental items. To ensure your jewelry isn’t stolen, it's best to keep it on your person or leave it at home and never in your car.

14. Cosmetics

High temperatures can cause makeup products like lipsticks, foundations and creams to melt, altering their texture and making them difficult or impossible to apply. Even products that don't visibly melt may undergo chemical changes that affect their color, consistency and effectiveness.

Extreme cold can cause the moisture in certain cosmetics to expand. Once the expansion reaches a certain point, it can cause a break in the container and lead to leaks inside your car.

15. Plants

Since the interior of a car can quickly become an oven under the sun, plants are vulnerable to wilting or even burning if left inside your car for long enough.^[2] Conversely, cold temperatures can freeze the plant's cells, causing damage that can be equally fatal. Furthermore, the lack of air circulation inside a parked car can increase humidity levels, encouraging the growth of mold or fungus.

16. Aerosol Cans

Leaving aerosol cans in your hot car can be extremely dangerous due to the pressurized contents inside the cans. As temperatures rise, the pressure inside the aerosol can increase, potentially leading to an explosion.^[7] Even if the can does not explode, the increased pressure can cause the canister to leak, releasing potentially harmful chemicals into the car's interior.

17. Low Gas Tank

Driving or leaving your car with a low gas tank, especially in colder weather, can lead to several issues beyond the risk of running out of fuel. In cold temperatures, condensation can form in an empty or nearly empty gas tank.

This water can then mix with the gasoline and, if it makes its way into the fuel lines, may freeze, potentially blocking the flow of fuel to the engine, causing starting problems or even engine damage.

Furthermore, consistently running on a low fuel tank can cause the fuel pump to overheat and wear out prematurely, as the fuel acts as a coolant for the pump. The debris at the bottom of the tank can also be drawn into the fuel system, leading to clogs and inefficiencies.

18. Sunscreen

It’s bad to leave sunscreen in the car because prolonged exposure to heat can encourage bacteria and fungi growth. The heat breaks down the preservatives which causes the prolific growth of these microbes. The heat can also degrade the active ingredients in chemical sunscreens, making them less effective for sun protection and exposing you to harmful sun rays.^[8]

Also, leaving spray sunscreen in the car can be even worse due to the pressurized container's sensitivity to high temperatures, which may lead to a risk of explosion or leakage.

19. Art Supplies

Storing art supplies in your car can lead to their deterioration and potential safety hazards, depending on the materials involved. Items like oil paints, spray paints and certain solvents are particularly sensitive to temperature changes. High heat can cause these materials to expand, potentially leading to leaks or, in the case of spray paint, even explosions. Cold temperatures, on the other hand, can cause some liquids to freeze, leading to separation and rendering them unusable.

20. Musical Instruments

Musical instruments are often sensitive to temperature and humidity changes and extreme heat can warp wood, melt glue and damage finishes, while cold temperatures can cause cracking and misalignment. For example, the delicate components of string instruments like violins and guitars are particularly susceptible to warping and neck bending.

21. Glasses

Extreme heat can warp or melt the frames of glasses, especially if they are made of plastic and can cause the lenses to become distorted. In the case of sunglasses, prolonged exposure to heat can also damage the UV protective coating, reducing their effectiveness in protecting your eyes from harmful UV rays. Similarly, cold temperatures can make certain materials brittle, leading to cracks or breaks, especially in older or more delicate frames.

22. Firearms

Leaving a firearm in your car can have serious consequences, as over one million firearms were reported stolen from 2017 to 2021. The majority of these thefts (96%) occurred from private citizens, with vehicles being a primary target.^[9] If you must store a firearm in your vehicle, be sure to comply with your state laws and local regulations.