By Ted Gansler, MD, MBA
An e-mail message that may have come into your inbox recently claims that dangerous levels of a cancer-causing chemical (benzene) are released from the plastic surfaces of automobile interiors. The e-mail recommends opening the vehicle's windows to remove the benzene before using the air conditioner.
Although benzene is linked to leukemia, very little research has looked at whether the interior surfaces of cars release dangerous amounts of benzene, and the information that is available does not support the e-mail's claims.
Let's break the message down and compare the claims with the facts.
Here is the e-mail message (this links to snopes.com, which is not affiliated with cancer.org or ACS)
And here's a point-by-point comparison of the claims and the facts:
Claim: My car's manual says to roll down the windows to let out all the hot air before turning on the A/C. WHY?
Fact: On a sunny day, the temperature in a parked car can be more than 40 degrees (Fahrenheit) higher than the outside air. Opening the windows is the fastest way to exchange the hot interior air with the cooler outside air. Once that is done, the air conditioner can make the interior cooler than the outside air. The manual's recommendation is probably focused on passenger comfort rather than toxicology.
Claim: No wonder more folks are dying from cancer than ever before.
Fact: Actually, the age-adjusted cancer death rates in the United States have been decreasing for the past 2 decades.
Claim: Please do NOT turn on A/C as soon as you enter the car. Open the windows after you enter your car, and then turn ON the AC after a couple of minutes. Here's why: According to research, the car's dashboard, seats, a/c ducts in fact ALL of the plastic objects in your vehicle, emit Benzene, a Cancer causing toxin. A BIG CARCINOGEN... Prolonged exposure will cause Leukemia and increases the risk of some cancers.
Fact: Benzene is known to cause cancer, based on evidence from studies in both people and laboratory animals. The link between benzene and cancer has largely focused on leukemia and other cancers of blood cells. Rates of leukemia, particularly acute myeloid leukemia (AML), have been found to be higher in studies of workers exposed to high levels of benzene, such as those in the chemical, shoemaking, and oil refining industries.
Some studies have also suggested links to acute lymphocytic leukemia (ALL) in children and to chronic lymphocytic leukemia (CLL) and other blood-related cancers, such as multiple myeloma and non-Hodgkin lymphoma, in adults. However, the evidence is not as strong for these cancers.
A German study published in 2007 specifically researching the air inside parked cars did not find a hazard to human health. Their analysis detected some cancer-causing chemicals and others that are considered probable or possible carcinogens, but these chemicals were present at levels similar to those found in the air of buildings. Some chemicals that are similar to benzene were found, but benzene was not reported in the results of this study.
Claim: Acceptable Benzene level indoors is: 50mg 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 the windows closed, will inevitably inhale, in quick succession, excessive amounts of the BENZENE toxin.
Fact: The standard way to report levels of chemicals in air is mass per volume (for example, mg per cubic meter or cubic foot), not mass per area (mg per square foot). Although this is a technical detail, it suggests that the authors of this e-mail may have limited knowledge of the basic scientific principles of this topic.
Furthermore, United States regulations do not specify any single acceptable benzene level. The National Institute for Occupational Safety and Health (NIOSH) has a limit for short-term (15 minute) workplace exposure (3.2 mg per cubic meter) and for average workday exposure ( 0.32 mg per cubic meter). So, the benzene level stated in the e-mail (recalculated as mg per cubic meter) as acceptable is between the NIOSH levels for short-term and daily exposure.
Another blow against this claim comes from the German study previously mentioned. It measured the level of a whole group of chemicals in a new car and an older car "parked in sunshine." Levels were higher in the new car than the old one, but still 1/10 of the level claimed in the e-mail for benzene alone (and, benzene was not even among the more than 40 chemicals recognized in the study).
Several other studies -- from Germany, South Korea, and the United States -- have looked at benzene levels in moving cars. These levels have ranged from 0.013 to 0.560 mg per cubic meter. The high range of these reports exceeds the NIOSH chronic exposure limit, though in the US study, the highest level (0.045 mg per cubic meter) was found in a car the researchers described as malfunctioning.
We found no published studies that confirm the claims of this e-mail. Benzene levels that exceed recommendations for chronic workplace exposure have been observed in some moving cars, but these levels seem unlikely in properly maintained cars.
Still, if you're concerned about benzene levels in cars (especially in cars with the engine running), there's no harm in opening the windows periodically or using an air-conditioner setting that circulates air from outside the vehicle.
And there are other steps people can take to reduce the amount of benzene to which they're exposed:
- Stay away from cigarette smoke. If you are a smoker, try to quit. Cigarette smoke is a major source of benzene exposure.
- If you are exposed on the job, talk to your employer about process changes (such as replacing the benzene with another solvent or making sure the benzene source is properly enclosed) or by using personal protective equipment. If needed, the Occupational Safety & Health Administration (OSHA) can provide more information or make an inspection.
- Try to limit gasoline fumes by pumping gas carefully and choosing gas stations with vapor recovery systems that capture the fumes. Avoid skin contact with gasoline, which contains benzene.
- Finally, use common sense around any chemicals that might contain benzene, like solvents, paints, and art supplies. Minimize or avoid exposure to their fumes, especially in unventilated spaces.
Ted Gansler, MD, MBA, is director of medical content for the American Cancer Society's National Home Office.