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Candles: What do they emit when lit?

Originally designed as a tool for light, heat and timekeeping, candles are more modernly used for birthdays, religious celebrations, or as decoration. But how do they actually work?

Catherine Wang is a biomedical science student at McGill University, specializing in anatomy and cell biology.


The use of candles dates back as far as 3,000 B.C., when ancient Egyptians used papyrus reeds dipped in animal fat that they then lit to use as torches. Similarly, ancient Romans dipped wicks into tallow, a rendered form of animal fat, to create another early form of the candle. Other components of candles include plants, insects, seeds and nuts which have been identified in Chinese, Japanese and Indian civilizations.

Thanks to its accessibility and affordability, tallow continued to be a popular ingredient for candle-making through the Middle Ages, particularly in England and France, where, like today, candles were a popular gift. Beeswax was also ideal since it gave off a bright flame and minimal smoke; however, it was much more expensive than tallow.

By the 18th century, the American whaling industry brought about the discovery of spermaceti, an oil sourced from the head of the sperm whale. This marked a large advancement in the development of candles since spermaceti wax was found to be both stiffer and less odorous than tallow. However, the production process for spermaceti candles was rigorous and lengthy, making it much more expensive and therefore accessible only to the wealthiest portion of the population.

The 1820s brought us stearin candles made of stearic acid that a French chemist discovered could be extracted from animal fat. Around the same time, chemists also figured out how to separate naturally occurring paraffin wax from petroleum, creating paraffin candles. We use both these types of candles today. These discoveries, coupled with the invention of a machine that streamlined the production of molded candles, revolutionized the production process.

These advances carried into the 20th century, where growth in oil and meat industries increased the availability of paraffin and stearin as byproducts, respectively. Today, they remain two of the most common materials used in candles, along with beeswax, palm wax and soy wax.

All the above mentioned building blocks for candles can be grouped as waxes. More specifically, they are all hydrocarbons.

When you light a candle, the heat of the flame melts the wax surrounding the wick. The melted wax vaporizes through a combustion reaction, where hydrocarbons interact with oxygen to break into its two components: hydrogen and carbon. This releases light, heat, carbon dioxide and water vapor, and fuels the flame. Some of this heat is reabsorbed by the wax, causing it to melt and replenish the liquid wax at the base of the wick, thus maintaining a stable burn.

As the candle burns, you’ll notice the melted wax pool beneath the flame. This wax acts as a fuel and if it encounters any water, it will react similarly to a grease fire and needs to be put out in the same way — by removing the oxygen.

There is some controversy regarding the safety of paraffin candles because of their emissions when burned. Many people have even swapped them out for what some say is a safer alternative: stearin candles. But is paraffin really all that bad?

A study conducted at South Carolina State University found that with paraffin candles, this combustion process also releases toxic chemicals such as toluene, which is a benzene derivative, a known carcinogen for humans. Since paraffin wax is derived from petroleum oil, the researchers suggest that using these candles frequently will cause “dangerous pollutants drifting in the air,” which can be harmful when inhaled. They advised consumers to use soy or vegetable-based candles instead, including stearin candles which are made of the oils and fats derived from animals and/or plants.

The National Candle Association (NCA) contested this claim, stating: “No scientific study has ever shown any candle wax, including paraffin, to be harmful to human health.” They added that the U.S. Food and Drug Administration has approved the use of paraffin in the production, packaging and process of food, and even medical applications.

The safety of paraffin wax was supported by a study in the Journal of Regulatory Toxicology and Pharmacology that found that scented paraffin candles do not pose any health risks when used under normal conditions. In this experiment, researchers used environmentally controlled emission chambers to evaluate the concentrations of possible harmful emissions. The researchers aimed to replicate candle use in normal households. They found that the highest estimated emission levels for fragrances, formaldehyde and benzene were well below the air quality exposure limits defined by the World Health Organization.

To summarize, while there have been concerns regarding the safety of paraffin candles, they have been deemed safe for consumer use by multiple studies and remains a popular option for candle production because of its ability to hold scents and colours, as well as its affordability.

Since stearin candles are made of animal and plant materials, they are generally found to be a safe and environmentally friendly option. A study found that stearin candles released 50% lower concentrations of soot and combustion products when compared to paraffin candles. With a high melting point, stearin also has a longer burning time than other waxes, allowing your candles to last longer.

The same study also found that during festive periods in cemeteries in Poland, there were large increases in benzene and toluene emissions because of the increased use of candles, many of which are often made of non-refined paraffin. The researchers reported that the level of emissions was comparable to emissions from transportation.

The truth is, inhalation of smoke in larger amounts will be harmful no matter the kind of wax. It can be difficult to decide what type of candle is right for you since most waxes are found to be safe in normal conditions. That being said, “normal” conditions may vary from person to person. As such, the safest option is to do your own research and to practice safe candle-use.

A few things to keep in mind to burn candles safely:

  • Avoid direct inhalation of the smoke
  • Only use candles in ventilated spaces
  • Always keep burning candles in view
  • Do not use water to put out candles
  • Extinguish candles before going to bed or leaving the area

@CatherineeWang

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