Why Your Car Windows Get That Nasty Haze On Them

We've all been there. You have a car that you want to keep showroom fresh, but you find yourself constantly cleaning the inside of the windshield. You think it's just dust, so you keep your windows closed and your climate control on its recirculate setting, but the glass keeps getting dirty. You look closer and realize that it's not just regular old dust, but some sort of gross film. This nasty haze continues to build up, making headlights and other street lighting blurry at night. It eventually reduces overall visibility. 

So what exactly is this hazy, disgusting, annoying film on the inside of your windshield? It's from your dashboard, and other pieces of your interior, and it is as gross as you might be thinking. It's a chemical residue that forms from a process called off-gassing, and not only is it annoying to keep clean, but like car seat foam, it could contain carcinogenic chemicals that are bad for your health.

Off-gassing — not to be confused with outgassing, which happens in scientific or factory environments — describes the release of chemicals, gases, and volatile organic compounds into the interior of a home or car under normal temperatures. During the manufacturing process, organic chemicals can get trapped in liquid or solid form and then be released as particulate matter and gases into the atmosphere. 

Those gases are actually what you're breathing in when you take a whiff of that new car smell. Inhaling the scent means you're inhaling chemicals like toluene, benzene, and formaldehyde. Plus, there are per- and polyfluoroalkyl substances, often referred to as "forever chemicals" because the components break down slowly over time. They can be found everywhere on the planet, so it's no surprise they're also in your car.

How do these chemicals end up there? Automakers decided that cars catching on fire were a bad thing, and some of these chemicals are used to make interior pieces fire-resistant. They are also used to help repel stains and water. Polybrominated diphenyl ethers, specifically, were the dominant chemicals used as flame retardants, but they were banned by the Stockholm Convention in 2019. However, there are several exemptions for automakers and suppliers, and the United States hasn't ratified the treaty and therefore isn't bound by it. That means you could still find these chemicals in new cars today.

The byproduct of off-gassing might not be the only thing causing your windshield to be hazy. One other significant cause could be coming from a coolant leak in your heater core. When that happens, coolant vapor can enter the cabin through the air vents and then condense on the vehicle's glass. You can tell because the film on the windshield will be sticky and will likely smell quite sweet, like how antifreeze smells. Just don't ingest it after you touch it.

Also, if you're a smoker or use a vape, the residue from that can build up on the glass. Certain interior detailing products might also condense on the windshield. Air fresheners can also be a culprit. Lastly, it could be caused by a dirty cabin air filter that needs to be replaced.

While there's no way to prevent the off-gassing residue from building up on your windshield, you can avoid excessive buildup by regularly cleaning the inside of your car windows. It won't completely protect you from the effects of off-gassing, but you can stay ahead of the buildup game and improve your overall visiblity.