Here’s Why Your Toilet May Actually Be Cleaner Than Your Car’s Interior

Not quite two years ago, those writing about automobiles—ourselves included—took to the task of priming motorists on the best ways to ensure their cars were COVID-free through cautious use of disinfectants and wipes. Turns out it was more difficult to catch the then-novel Coronavirus just by holding onto a steering wheel or gear shifter that had been in someone else’s hands a day or two earlier than we feared

For better or worse, many (if not most) of us have abandoned the notion of keeping our vehicles as germ-free as possible. But a recent report conducted for the U.K. website Scrap Car Comparison by Aston University in Birmingham, England concluded that we might be better off returning to our old obsessive-compulsive selves when it comes to maintaining a healthier ride.

The study, which took place last December, found that bacterial contamination levels found in five models of varying ages were significant higher than that found on the average domestic toilet. Worse, the area that tends to suffer the worst germ infestation is where most of us bring provisions home from the grocery store. 

That would be the trunk, where researchers found, “significantly high levels of bacteria that includes E.coli” Also known as faecal bacteria, E.coli has the potential to wreak havoc with one’s digestive system. They also found a high concentration of bacteria on the cars’ drivers’ seats, which you should think about next time you grab a quick bite from the drive-thru window and consume it while en route.

Other parts of a car tested included the gearstick, dashboard and backseat, where testing discovered higher levels of bacterial contamination than would otherwise be found on, or inside, a typical home’s toilets. The bacteria identified included Pseudomonas, a bacterium with strains that can’t easily be treated with antibiotics and Staph Aureus, a germ associated with coughs and sneezes that in some cases is linked to MRSA. 

Interestingly, the report determined that older cars sampled tended to collect higher levels of bacterial loads, aggregated over time, than newer models. “The results of this study are fascinating, as they help to show that despite cleaning our cars, the older they are, the dirtier they generally are,” says Dr. Jonathan Cox, Senior Lecturer in Microbiology at Aston University. “These results highlight that we should instead change how we think about our cars and cleanliness. Often, we will clean our cars based on whether they ‘look’ clean versus whether they actually are clean, but you would never even think about eating off of your toilet seat.”

Indeed.

If there is a bright spot to be found in Scrap Car Comparison’s cleanliness report, it’s that researchers determined the steering wheel, which one might think would be a haven for bacteria, is actually among the least germy touch points on the average automobile. That can likely be attributed, it’s believed, to the sudden and frequent use of hand sanitizer as the pandemic began to take hold. 

Aside from wiping down the dashboard, steering wheel, interior trim, switches, and knobs with antibiotic surface cleaners, it’s suggested motorists shampoo the car’s upholstery periodically, which is too often subjected to spilled drinks, dropped chips, and—to put it delicately—gassy passengers. 

“The bottom line is that people generally do not typically get ill from the bacteria in their cars, because we naturally do things in our everyday lives (such as hand washing) to reduce the impact, says Dr. Cox. “However, knowing the bacteria that can build up in our cars can be really useful in cleaning our cars properly and regularly, and reducing any risks.”

Here are the areas within a typical automobile the study found most prone to bacterial growth:

1. Trunk – 1,425 bacteria identified 
2. Driver’s seat – 649 bacteria identified 
3. Gearstick – 407 bacteria identified 
4. Back seat – 323 bacteria identified 
5. Dashboard – 317 bacteria identified 
6. Steering wheel – 146 bacteria identified

You can read the full report here.

The Fine Print

Samples were taken by swabbing location within five used cars using a sterile cotton bud swab, hydrated with phosphate-buffered saline. Each swab was spread onto a Nutrient Agar (NA) and a Violet Red Bile Glucose (VRBG) culture medium. NA supports all bacterial growth, whereas VRBG only supports the growth of Enterobacteriaceae (faeces). Inoculated agar plates were incubated at 37 degrees Celsius for 24 hours to enable bacterial growth. All colonies were enumerated and subject to the Gram staining method to enable presumptive identification, from which all results were gained. Two domestic toilets were chosen that had not been knowingly cleaned, but had been used in the preceding 24 hours.