When you take a stroll down the household cleaning aisle in supermarkets or pharmacies, you are bound to see shelves of indoor or car air refreshers, incense, essential oils, candles and candle burners. In climate-controlled indoor environments where opening a window may not be an option, many people rely on these types of products to eliminate odor or stale air at home and in their cars, or just to set the mood for the environment. But, how much do we know about these products and their potential impact on our health?

According to a Statista report, based on the U.S. Census data and Simmons National Consumer Survey (NHCS), 158.97 million Americans used air freshener spray and room deodorizers in 2011, and the numbers rose to 179.49 million in 2016. Plug-ins/electric air freshener products came in second with 71.29 million, and then candles at 52.43 million. Potpourri, which shows a downward trend in popularity, has the least users at 10.13 million.

While it is not a major issue with occasional usage, UL’s lead scientist Elliott Horner says that long-term exposure to by-products of candles and incense, for example, can potentially bring about lung and heart diseases.

“Burning things generates soot, regardless of how ‘clean’ the burn is. Soot is fine particulate matter (PM), and the numbers are related to the size of the particle, irrespective of composition materials,” he says.

The EPA’s Web page explains that PM contains microscopic solids or liquid droplets that are so small that they can easily be inhaled and cause serious health problems. Dust, pollen and mold would come under a particle pollution of PM10 (less than the width of human hair) which can increase risk of lung disease; and combustion particles, organic compounds, and metals are categorized under PM2.5 which can be one of the causes of coronary heart disease.

Echoing Horner’s observation on the hazards that may jeopardize indoor air quality, Scott Steady, UL’s senior product manager, says that there are also alternative - less reactive, non-combustible - products such as gels and oils that are also being used which may not have the same potential health impacts, but still do emit chemicals.

Some brands may tout their low volatile organic compounds (VOC), but Steady says that “Fragrances are formulated in different ways, and you may be breathing in particles emitted from synthetically made products. Then there are different grades of paraffin or soy waxes which melt at lower temperatures but may contain compounds that can be toxic.”

Steady adds that unlike Europe, where the European Committee for Standardization (CEN) places great emphasis on ensuring manufacturing guidelines are met for producing air deodorizing products, there are no similar significant research or guidelines in the U.S. It is up to consumers to take voluntary steps to reduce risks associated with the products.

Both Horner and Steady say that firstly, the simplest way to keep the air in your house and car fresh is to open the windows.

Reducing the sources of indoor air pollutant is another step to take towards breathing better quality air. While it is nice to have air refreshers and similar products to make homes smell good, controlled usage would help maintain day-to-day indoor air quality.

Thorough housekeeping in a still-air environment is highly recommended if your house is stained with soot and stale remnants of the used air deodorizing products.

As Horner says, everyone will balance risks and benefits differently, but it helps to ask ourselves what the value of warmth, aroma or light that these products bring today is, as compared to the possible negative effects that heavy usage may bring in the future.