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Making “Scents” of Indoor Air Quality and Candles

red candle burning

As the cooler temperature of autumn rolls in, many people can not wait to get the windows open and light up their favorite pumpkin pie scented candle. Candles can add a relaxing fragrance to your home, and are a huge business in the US. Estimates show that annual candle sales in the US approach $2 billion1. However, burning candles also have an effect on indoor air quality and can cause extreme respiratory problems in some people.

How Candles Work

When it boils down, candles are very simple. They consist of a blend of volatile and semi-volatile chemicals which are suspended in a wax matrix.  The chemicals determine the makeup of the scent and add fuel for burning. The wax can be made from a number of different materials such as petroleum-based paraffin wax or natural-based beeswax or soy wax. A wick, which commonly is made from cotton, is placed inside the wax. When the wick is lit, capillary action will draw the melted wax mixture up to the tip. From there it ignites and releases the compounds inside the wax into the air.

Common “Scents”

Like nearly all artificial scents inside of a home, candles can cause air quality problems. The chemicals in the wax, scents, and dyes that are released into the air can trigger asthma or affect people who have chemical sensitivities. Low levels of organic chemicals, including acetaldehyde, formaldehyde, acrolein, and naphthalene have been documented in laboratory research 2 Levels of selected organic compounds in materials for candle production and human exposure to candle emissions. Chemosphere, 34(5-7):1623-1630.). The burning of the wick can produce particulate matter, especially in candles inside jars, which limit combustion. When air is limited, the candles can often give off much more soot and smoke than a candle that is open to the air. This soot can deposit on surfaces in the area and more than once we have been out to a property for a “mold issue” only to discover the discoloration is “ghosting” from burning candles. 

Prior to 1974, lead was commonly used in candle wicks. Now, the US candle industry has voluntarily removed lead wicks from production, however, lead wicks can be found in imported candles still to this day. Candles can also pose an increased fire risk. While not a direct effect on indoor air quality, even a limited fire can be catastrophic to property and life inside the home and an increased risk should not be ignored. Another consideration is that some people use candles and air fresheners to cover up unpleasant odors. Masking these odors does not make the issues go away, and adding new sources of chemicals into the air is actually making the issues worse.

Indoor Science can assess any of your indoor air quality concerns. You can contact us to learn more about our services and what we can do to help.


  1. https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P1009BZL.txt
  2. Lau C, Fiedler H, Hutzinger O, Schwind KH, Hosseinpour J. 1997.
Ian Cull

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”