The Emission Studies

In which we enter a murky wacky world of mumbo-jumbo, clarity, and soot.

My lifelong experience with paraffin had been so innocuous and what I was reading about it in “The Chemistry and Technology of Waxes” seemed so benign, yet interesting, that I decided it was time to delve into some candle emission studies to try to uncover why there was all this online hullabaloo (among some) about paraffin being poisonous. I searched out and read several studies, but only those that I could find online, for free, and when it seemed to reach the point of enough said, I stopped. So I am sure I did not cover the whole gamut of what is out there. But, that said, if online claims that paraffin candles are toxic are linking to any research, they are not linking to any research I have not read. That said, please recall I am not a chemist and understanding some of the terminology and numbers and particulars in these studies is beyond me. But, that said, some parts of these studies are written in plain—or nearly plain—English. Those are the caveats. Here we go.

“Candles and Incense as Potential Sources of Indoor Air Pollution: Market Analysis and Literature Review” is an EPA report from January 2001. Its conclusion, after dealing with the problem of lead wicks, which were banned in the U.S. many years ago, is this: 
Lead wicks aside, consumers are also exposed to concentrations of organic chemicals in candle emissions. The European Candle Association (1997) and Schwind and Hosseinpour (1994) conclude that there is no health hazard associated with candle burning even when a worst-case scenario of 30 candles burning for 4 hours in a 50 m3 room is assumed. However, burning several candles exceeded the EPA’s 10-6 increased risk for cancer for acetaldehyde and formaldehyde, and exceeded the RfC for acrolein. Once again, the RfC and EPA’s 10-6 increased cancer risk guidelines are not designed specifically for indoor air quality issues, so these conclusions are subject to interpretation.
The report introduces us to soot.
Black soot is the product of the incomplete combustion of carbon-containing fuels. … ¶ Scented candles are the major source of candle soot deposition. Most candle wax paraffins are saturated hydrocarbons that are solid at room temperature. Most fragrance oils are unsaturated hydrocarbons and are liquid at room temperature. The lower the carbon-to-hydrogen ratio, the less soot is produced by the flame. Therefore, waxes that have more fragrances in them produce more soot. In other words, candles labeled “super scented” and those that are soft to the touch are more likely to generate soot.
I found two abstracts of studies conducted in Italy, funded by the Associazione Cerai d’Italia. The first, “Emission of air pollutants from burning candles with different composition in indoor environments,” looked at the emissions from different paraffin waxes in “container” candles, which I took to mean a candle contained in a jar or cup. There isn’t much to the abstract, but there is this: 
It has been found that wax quality strongly influences the air pollutant emissions.
The other study, by the same researchers, is “Emissions of air pollutants from scented candles burning in a test chamber.” 
Burning of scented candles in indoor environment can release a large number of toxic chemicals. … This paper investigates volatile organic compounds emissions, with particular reference to the priority indoor pollutants identified by the European Commission, from the burning of scented candles in a laboratory-scale test chamber. It has been found that BTEX and PAHs emission factors show large differences among different candles, possibly due to the raw paraffinic material used, while aldehydes emission factors seem more related to the presence of additives. …
The Schwind and Hosseinpour study mentioned in the EPA report comes from Germany. It has the unwieldy title “Determining and Evaluating the Emissions of PCDD/PCDF, PAH and Short-Chain Aldehydes in Combustion Gases of Candles.” For what it’s worth, PAH is “polycyclic aromatic hydrocarbons” and PCDD/PCDF is “polychlorinated dibenzo para dioxins/polychlorinated dibenzofurans.” But please don’t quote me on that. The study looked at waxes, wicks, emissions, and toxicity. 
Even with an assumed “worst-case scenario” and allowing for governmental limits and specifications, the toxicological evaluation arrived at the result that the examined candles do not cause any additional health risk.
Beeswax, paraffin, and stearin candles were tested with nine of the same type being burned simultaneously with controlled air turbulence. This study seems to have the most information but, unfortunately, it’s not information I fully understand. For instance: 
Although the beeswax used for the candles showed higher PCDD/PCDF and chlorophenol contaminations than paraffin and stearin waxes, the PCDD/PCDF emissions in the burn tests, with 4 femtogram/g of wax burned, are the lowest (refer to Table 4). The conditions of combustion in the candle flame were apparently suited to reduce PCDD and PCDF. The corresponding emission values for paraffin and stearin candles range slightly higher.
And here is Table 5, a beautiful mass of indecipherability, which is sometimes the best way to see—and leave—things.

The conclusion that Schwind and Hosseinpour arrived at, though, is clear:
The measuring program has shown that the burning emissions of the examined candles do not represent a potential health hazard to the candle user. The burn emissions of the examined paraffin, stearin and beeswax candles show no significant differences with respect to the pollutant classes examined. Candles made from paraffin are toxicologically just as innocuous as beeswax or stearin candles. These conclusions apply also to the three wick types used.¶ It should be noted, though, that exclusively noncolored candles without decorative additives were used …
So in 1994 a candle emissions study cited by an EPA report in 2001 finds that “Candles made from paraffin are toxicologically just as innocuous as beeswax or stearin candles.” I emphasize this finding because the next study ignores it.

“Soybean Candles for Healthy Life and Well Being” begins with a definitive statement, which I copy and paste:
Several studies of candles indicated that paraffin wax candle burning could cause serve health problems from the harmful burning emissions.
The “several studies” are not named and I could not find them. Sponsored by the National Institute of Food and Agriculture (part of the USDA) and directed by Ruhullah Massoudi, a chemistry professor at South Carolina State University, this study, or, should I say, the document I found related to the study, is basically a series of progress reports spanning 2006 to 2010. Within it I never found a citation or evidence for the project’s contradictory premise that there are “health problems associated with the use of petroleum based candles.” I did find a lot of funny stuff.

Under a section labelled “Goals / Objectives”:
The second objective is to address the economical feasibility of replacing a renewable source like soybean for petroleum source, which is not renewable and depletes and depends on foreign import. Beyond that, using soybean would bring a healthy economy to our farmers by producing more and better products.
Under “Project Methods”:
Apparently, this research is necessitated because of the health problems related to the use of petroleum based products. By replacing paraffin wax with soy wax in candles, an estimated 60 million pounds of soybeans would be required for annual candle production. This requirement will have a direct economic impact on soybean farmers as well as a health and environmental impact in this country. The burning of soy candles in homes and cars address the real issue at hand, which is the health of American and global consumers. The burning of paraffin candle gives off more toxic fumes than soy candles which may be harmful to individuals.
I am so curious: Who burns candles in cars?

Under “Impact”:
Economically, paraffin candles produce carbon which is ruining the furniture, walls, cloths, which is expensive to clean or remove the effect. Therefore, the overall impact of this project is beneficial for the entire population of the world, nations and governments to have healthy and productive generations. Considerable adverse health effects including cancer, asthma, and dermatitis as a result of burning paraffin wax candles in enclosed limited areas have been reported. The composition of emission products are identified by using a GC/MS system equipped with a NIST Library of compounds. The chromatogram of emission products of paraffin based candles were tested for hazardous emissions. In support of published reports the petroleum based candles produced various alkanes, alkenes, toluene, benzene (a carcinogen) and some other chemicals whereas the soybean candle was completely clean. Apparently, petroleum based candled produce chemicals that are health hazards and producing chemicals that should be avoided. Our presentation of results had a great impact in scientific community, general public and candle making industry all over the globe. This resulted reflections of world media causing enormous publicity for the university, and public awareness. The American agricultural economy would greatly benefit by the production and burning of soy wax candles instead of paraffin candles. …
Indeed, this soy candle project garnered “enormous publicity.” Any article about how your romantic paraffin-candlelit dinner is toxic stemmed from this study and the number of times I have seen sentences or parts of sentences taken from this study and plopped into “wellness” blogs and in the promotional material of beeswax and soy candlemakers, without citation or clarification, is legion and mind-boggling. It seems from this one haphazard project everyone swallowed whole a notion that paraffin is toxic.

Well, not everyone, not whole. Although NPR did lead off their reporting with an alarm about paraffin candles polluting your home, they then walked it back a bit. Massoudi, they reported, along with his undergraduate assistant “ … caution their work so far has been only qualitative and hasn’t put numbers on the stuff spewed out by candle combustion. … (they) can’t say much about the potential health effects at this point … ”. You mean they can’t say anything about health effects after everything they’ve already said about health effects? NPR also suggested that the USDA “wouldn't mind if soybean-based candles became the rage.”

As to be expected, the European Candle Association refuted the study outright, and the National Candle Association in 2017 issued a press release that begins:
The National Candle Association (NCA) is calling upon the leadership of South Carolina State University to remove information from its website about research that the trade association says is erroneous, unsubstantiated and misleading.

In letter to South Carolina State University president James E. Clark, Dr. John Heinze, science consultant to NCA, explained that the research, conducted by university faculty member Dr. Ruhullah Massoudi and an undergraduate student, was flawed from the start and that statements about the study included in a university press release are without merit. The press release remains on the SCSU website despite the fact that the study has not been published, or subject to scientific peer review in the years since a summary of the study was presented at a scientific conference (August 2009). Further research on this topic has not been reported by the authors, nor has Professor Massoudi responded to a previous NCA letter in 2015 pointing out the scientific errors in the study.
Industry is not without its drama.

So it begins to look as if the whole “paraffin is toxic” thing was just something cooked up by a few soybean hopefuls looking to expand their market by dissing, dousing, and slandering the competition. They used a scare tactic, and that such an unfounded claim could spread like a fueled flame should, I suppose, come as no surprise. After all, the idea plays extremely well; it’s almost too easy. Imagine: In your home you are burning a product related to gasoline and kerosene and crude oil and diesel fuel. Now imagine: In your home you are burning a product related to a leafy green plant, or, better yet (if you are not a vegan), a product of the honeybee—a creature we must save—a creature who sipped nectar from a flower and aren’t both our honeybees and soybean plants bumbling about in a delightful breeze on a lazy, sun-drenched, summer’s day? Which picture spells dirt and doom? Which picture plays clean and light?

At the time of the soybean-candle-for-healthy-life project, candles made from soy wax, which is manufactured from soybean oil and the candles usually scented in various ways, had been on the market ten years or so. Candles made with paraffin had been in use for more than a hundred years. Why is it so easy to forget that? Why is it so easy to forget that millions of people over several decades had been using paraffin candles and suffering no harm? Unless, of course, the candle somehow caused a fire. Perhaps that is the “real issue at hand.”

There is another study that people tend to lift from as proof of the toxicity of paraffin that takes us right into another real issue: soot and scent. “Characterization of Scented Candle Emissions and Associated Public Health Risks” is a 1999 Master’s thesis by David Krause. The best I could find was an extract of the paper, but it has the key elements that many have cited, including a bit about diesel soot. After analyzing emissions from 91 paraffin candles, some scented and some not, Krause states: 
The possible impacts on public health from consumer use of scented candles may include increased risk of cancer, neurological and behavioral deficits and acute aggravation of existing respiratory diseases such as asthma.
Most of the risk, he says, comes from the soot that scented candles emit to a much higher degree than non-scented candles. He draws a similarity between diesel soot and candle soot as they “share the same physical and many of the same chemical properties which are believed to contribute to both toxicity and carcinogenicity.” There are existing reference points for diesel soot; there are no such reference points for candle soot. So Krause draws a similarity between the two in order to apply one’s reference points to the other.
Due to the current absence of information on scented candle emission toxicity, and its numerous similarities with diesel exhaust, it would be prudent to tentatively adopt the recognized toxicity values for diesel emissions until specific testing can be accomplished.
He goes on to say: 
When the unit cancer risk for diesel exhaust is applied to exposures to candle soot, the estimated increased cancer risk for a lifetime exposure, would range from 9.7 x 10-5 to 3.0 x 10-4 for the lowest emitting candle to 1.5 x 10-2 to 4.7 x 10-2 for the highest emitting candle, using the range of unit cancer risk of 2.9 x 10-5 to 9.0 x 10-5 per m g/m3.
If you can tell me what those numbers mean, well, give it a try.

In his summary, Krause states:
Use of scented candles may contribute significant quantities of pollutants to the indoor environment, especially soot, benzene and lead. Dozens of other compounds were identified in individual candles, but their contribution to occupant risks were not characterized in this limited scope risk characterization. Due to the variability in candles and their respective emission rates, great uncertainty would exist in a generalized risk assessment.
Krause’s “Black Soot Deposition: How It Impacts IAQ” (Indoor Air Quality) was published in 2001 by The Refrigeration Service Engineers Society Journal. It is readable and clear, addressing an increase in the number of complaints about soot build-up in homes received by the Florida Department of Health in the 1990s. Krause explains what soot is (“a product of incomplete combustion of carbon-containing fuels”) and explains that a blue flame indicates complete combustion, a yellow flame incomplete combustion. As it turned out, the soot that people were complaining about could be traced back to candle usage, and, in particular, the use of certain types of candles and, as well, the manner in which the candles were burned. 
In effect, burning one of these candles can be equivalent to burning 100 candles at once. It also was determined that a candle placed in an air draft can increase its soot production by a factor of 50.
Krause does not differentiate by wax type—all his test candles appear to be paraffinic. But here is his list of what to avoid in a candle: 
Candles poured into glass jars or ceramic containers.
Soft wax containing unsaturated hydrocarbons.
Aromatic (scented) wax containing volatile aromatic hydrocarbons.
Thick, long wick or one with a wire core.
Soot deposits on the mouth of the jar.
High, erratic flame when burned.
Visible soot emitted from an erratic flame.
Located in an air draft created by a fan or a/c vent.
Pillar candle with signs of uneven burning or thick, erect wicks.
Multiple wick candles with thick, erect wicks.
And here is his list of what to look for in a candle if you wish to avoid excessive soot:
Hard wax containing mostly saturated hydrocarbons.
Thin, braided wick that curls over when burned.
Low aromatic properties.
Tapered and votive candles with thin wicks.
Those that have a low, even flame when burned.
How airborne candle soot circulates captured my imagination. Initially particles float around on air currents, potentially inhaled, but eventually soot particles succumb to gravity and attraction, landing here and there in the home. Soot build-up is described as black streaks on walls, curtains, blinds, and carpets. Krause explains that soot is attracted to cooler surfaces due to thermophoresis, and that soot is also “attracted to electrically charged surfaces … ” And I ask you, how could this not bring to mind negative ions being attracted to positive ions? Have you not heard the story about beeswax candles emitting negative ions that clean the air by latching on to positive ions free-floating in your home’s air and how these positive and negative ions conjoined then drop out of the air, thus cleansing the air, and … go where? Could this explanation of what soot does—attaching itself to electrically charged surfaces—be at all related to this malarkey I’ve heard about beeswax, negative ions, and clean air?

Alleged malarkey.

In conclusion, I did not find any evidence that an unscented, well-made, high quality paraffin candle burned responsibly should for any reason detract from your romantic candlelit dinner nor potentially kill off your lover nor dirty your tablecloth with sooty black streaks unless, of course, someone at this romantic candlelit dinner gets too excited, knocks over the candle, sets the tablecloth aflame, and, blooey, that’s it. I do think there is enough evidence to be suspicious of candles that are not well-made, that are made of low-quality wax, that are wrapped up in jars, that are scented. But, if whatever is spewing from any particular candle you are burning isn’t bothering you, why worry? And if it is bothering you, stop burning it. Try an unscented candle, try something not in a jar, or try beeswax. It comes by its scent naturally—no added oil—and it stands on its own—no walls necessary.

But of course, I am no a chemist.

It should not have been omitted that previous to completely stripping the body of the leviathan, he was beheaded.
Herman Melville, Moby Dick

The Chemistry and Technology of Waxes
Candles and Incense as Potential Sources of Indoor Air Pollution: Market Analysis and Literature Review” U.S. Environmental Protection Agency, 2001
Emission of air pollutants from burning candles with different composition in indoor environments” Derudi, M., Gelosa, S., Sliepcevich, A. et al. Environ Sci Pollut Res (2014) 21: 4320.
Emissions of air pollutants from scented candles burning in a test chamber” Science Direct, 2012.
Determining and Evaluating the Emissions of PCDD/PCDF, PAH and Short-Chain Aldehydes in Combustion Gases of Candles” Schwind, K., Hosseinpour, J., Fiedler, H., Lau, C., Hutzinger, O., 1994.
Soybean Candles for Healthy Life and Well Being” USDA, 2006-2010.
Candlelight: A Dash Of Toxin With Your Romance? Hensley, S. National Public Radio, August 20, 2009.
US Trade Association Calls on South Carolina State University to Stop Promoting Bad Science, National Candle Association Press Release, 2017
Characterization of Scented Candle Emissions and Associated Public Health Risks” Krause, D. 1999.
Black Soot Deposition: How It Impacts IAQ” Krause, D., The Refrigeration Service Engineers Society Journal, 2001.

This page added 1/29/19.