While most people commonly think of car exhaust when naming the big causes of city pollution, the University of Colorado released details from a new study showing household products are now just as bad for smog.

Denver is no stranger to smog, as the city is often covered by a gray haze visible most readily from the northeast of the city. Usually, that is blamed on cars: you'll see warnings on roadways asking people to carpool if it's going to be especially bad.

But air quality is being lowered not just by car exhaust - but by household cleaners, perfumes, paints, pesticides and even lotion, according to a new study from the Cooperative Institute for Research in Environmental Sciences (CIRES) based at CU-Boulder.

"Chemical products that contain compounds refined from petroleum, like household cleaners, pesticides, paints and perfumes, now rival motor vehicle emissions as the top source of urban air pollution," says a spokesperson for the study, in a news release.

CIRES is a partnership between the National Oceanic Atmospheric Administration Chemical Sciences Division - a federal organization - and CU-Boulder.

Even though people use a lot more fuel than they do petroleum-based compounds (15 times as much), lotions and other household products contribute just as much to our low air quality, says the study's lead author Brian McDonald.

The study also claims that emissions from household products are twice as high as vehicle exhaust. The info was published in the journal Science.

“As transportation gets cleaner, those other sources become more and more important,” McDonald was quoted as saying in the news release. “The stuff we use in our everyday lives can impact air pollution.”

The combined fumes from every painting job in Denver, every open container of lotion, every hairspray and perfume spritz - it all adds up.

This study is at odds with the Environmental Protection Agency's current understanding of air pollutants in cities. A spokesperson says the EPA views the car exhaust/household products split as 75/25, it's actually closer to 50/50.

Even though car fuel is burned at a much higher rate and volume, the study's authors claim it's how household products are used that's to blame.

Think about it: you store gasoline in your gas tank, or in a gas can. Both things are usually airtight and only used when needed. However, lotions and perfumes are worn on the sleeve - for all to smell and enjoy.

For Los Angeles, household products have already overtaken car exhaust as the leading contributor to car exhaust, the study claims.

What's most concerning, the study continues, is that household products, while still high in the Denver sky, are ten times higher indoors.

As far as car exhaust is concerned - and the fight to reduce them - the study paints a bright picture:

According to a co-author of the study Joost de Gouw, the new assessment does find that the U.S. regulatory focus on car emissions has been very effective in reducing them.

The study's authors now say the fight against air pollution can no longer be one dimensional - it needs a multi-faceted approach.

According to a scientist with NOAA, the study does not make any claims about whether or not household product pollution is more harmful than car exhaust - only the amount of pollutant.

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The NOAA reached out to 9NEWS about this story to clarify that while pollutants were higher in some instances, the study did not look into the health effects of those pollutants. This story has been updated to reflect that fact.