Toxic Benzene and Parked Cars

Parked car
Zoran Milich/Moment Mobile/Getty Images

This viral message claims car interiors contain toxic levels of cancer-causing benzene emitted by dashboards, car seats, and air fresheners, and recommends opening windows to expel trapped benzene gas before turning on the car air conditioner. True or false?

  • Description: Online rumor
  • Circulating since May 2009
  • Status: Grain of truth / Overblown (see details below)
  • Example: Email text contributed by Glennis A., May 11, 2009:
    Car A/C (Air Conditioning) MUST READ!!!

    Please do NOT turn on A/C as soon as you enter the car.
    Open the windows after you enter your car and turn ON the air-conditioning after a couple of minutes.

    Here's why:

    According to a research, the car dashboard, sofa, air freshener emit Benzene, a Cancer causing toxin (carcinogen - take time to observe the smell of heated plastic in your car).

    In addition to causing cancer, Benzene poisons your bones, causes anemia and reduces white blood cells.

    Prolonged exposure will cause Leukemia, increasing the risk of cancer. May also cause miscarriage.

    Acceptable Benzene level indoors is 50 mg per sq. ft.

    A car parked indoors with windows closed will contain 400-800 mg of Benzene. If parked outdoors under the sun at a temperature above 60 degrees F, the Benzene level goes up to 2000-4000 mg, 40 times the acceptable level...

    People who get into the car, keeping windows closed will inevitably inhale, in quick succession excessive amounts of the toxin.

    Benzene is a toxin that affects your kidney and liver. What's worse, it is extremely difficult for your body to expel this toxic stuff. So friends, please open the windows and door of your car - give time for interior to air out - dispel the deadly stuff - before you enter.

    Our Analysis

    While it isn't one hundred percent false, the above text is a font of misinformation. Don't let it scare you.

    Starting with the basics, it's true that benzene is a toxic chemical known to produce a variety of ill health effects, including anemia and cancer (specifically leukemia) in humans.



    The substance occurs both naturally (mainly as a component of crude oil) and as a byproduct of human activities, e.g. as a component of petroleum-based products (such as gasoline) and products manufactured using benzene as a solvent (such as plastics, synthetic fibers, dyes, glues, detergents, and drugs). It's also a constituent of tobacco smoke.

    Low levels of benzene are typically present in outdoor air due to automobile exhaust and industrial emissions. Thanks to vapors emitted by household products such as glues, paints, and furniture wax, even higher levels of benzene can sometimes be found in indoor air, especially in new buildings.

    Benzene in Cars

    Do automobile dashboards, door panels, seats, and other interior components emit benzene, as claimed in the email? Most likely. In most cars, these items are made from plastics, synthetic fabrics, and glues, some of which are manufactured using benzene. According to scientists, such items may "off-gas" trace amounts of benzene, especially under hot weather conditions.

    As to car air fresheners, there's precious little information available about the ingredients, though one European study found that some household air fresheners emit measurable amounts of benzene.

    It's not inconceivable that some car air fresheners do, too.

    The crucial question is how much. Might all of these potential emitters cumulatively give off enough benzene to harm your health?

    What the Scientists Say

    Most of the published studies wherein benzene levels were measured inside passenger vehicles have been done under driving conditions, in traffic. So, while such studies have indeed found that in-vehicle benzene levels can significantly exceed those outside the vehicle, and could pose a human health hazard, this is mainly attributed to the presence of exhaust fumes.

    Also, the amounts of benzene actually detected by researchers, albeit statistically significant, were much, much smaller than the amounts stated in the email. A 2006 study summarizing all the data collected to date reported in-vehicle benzene levels from exhaust fumes ranging from .013 mg to .56 mg per cubic meter — a far cry from the 400 mg to 4,000 mg per square foot (do they mean cubic foot?) reported in the email.

    Benzene Levels in Parked Cars

    In the one study, we were able to find that measured benzene levels inside parked cars with their engines turned off. The results were more benign. Toxicologists took samples of the air inside both a new and a used vehicle under simulated hot-sunlight conditions, measuring the levels of volatile organic compounds (VOCs) including C3- and C4-alkylbenzenes, and exposing human and animal cells to the samples to determine their toxicity. Despite the detectable presence of VOCs (a total of 10.9 mg per cubic meter in the new car and 1.2 mg per cubic meter in the old car), no toxic effects were observed. Apart from noting the slight possibility that allergy-prone individuals might find their condition exacerbated by exposure to such compounds, the study concluded there is "no apparent health hazard of parked motor vehicle indoor air."

    When in Doubt, Ventilate

    Despite this finding, some drivers may still be concerned about the presence of any benzene vapors inside their car, especially given the World Health Organization's stated position that there is "no safe level of exposure" to the carcinogen. They may also worry, per the email warning above, that turning on the vehicle's air conditioner might exacerbate their exposure to trapped toxins by recirculating contaminated air. If that's the case, there's no harm done — and much peace of mind to be gained — by simply opening the windows and ventilating the car before turning it on.

    Sources and Further Reading

    • Benzene Facts: Centers for Disease Control and Prevention, 22 February 2006