Some years ago, Diwali meant lighting up rows of simple, eco-friendly, inexpensive diyas filled with oil and fitted with a cotton wick. It has acquired a modern twist — rows of tiny, sparkling electric lights, coupled with tealight candles placed in colourfully painted diyas decorate the exteriors of houses, while candles placed in artfully crafted containers add brightness to the interiors.
Today, a wide range of candles is available. Besides those made from paraffin wax, a petroleum byproduct, you can get candles made of natural products such as beeswax, soya wax, coconut oil wax, palm wax and stearin wax, which is made from animal fat or palm oil. There are also candles infused with aroma, some derived from chemical sources, others have essential oils extracted from plants. Their increasing use — not just for festivals and religious functions, but also for creating a certain ambience, for relaxation, aromatherapy, and even candlelight marches — has led to considerable research on candles as a source of indoor pollution.
Perhaps the most debated study was presented at the 238th national meeting of the American Chemical Society in 2009. Conducted at the South Carolina State University, it stated that burning candles made from paraffin wax released potentially harmful carcinogens, which could build up in closed rooms. Also published in 2017 in the International Journal of Tropical Disease and Health, the study pointed out that paraffin candles produced various hazardous products, including benzene and toluene, known carcinogens, and concluded that paraffin candles are hazardous to human health when burnt in enclosed and limited areas. This was strongly contested by the association of candle-makers in the US.
Another study, published in the Bulletin of Environmental Contamination and Toxicology in 2013, reported considerable increase in benzene, toluene and styrene emissions at public cemeteries during All Saints’ Day at two locations in southern Poland. During the seven-day intense candle-burning, the emissions from candles were similar to transport emissions, it said. Another research published the previous year in Atmospheric Environment recorded emissions of volatile organic compounds and aromatic hydrocarbons from scented candles burnt indoors.
Yet another research work in 2014 concluded that “under normal conditions of use, scented candles do not pose known health risks to the consumer”.
Published in the Journal of Environment International in 2021, another study monitored the typical combustion gases, particulate and ultrafine particles from the burning of soy, paraffin, palm and stearin candles. It said that in most cases, the calculated indoor concentrations were well below the guidance and reference values. The study also said that palm, paraffin, soya, and stearin behaved similarly in terms of emissions. However, candles without fragrances produced lesser emissions of combustion byproducts, it said.
While most researches concentrated on the emission of volatile organic compounds, a study on candle safety by the Danish Environment Protection Agency (DEPA) investigated (report published in 2017) the most hazardous of emissions — heavy metal and particulate. It found that white stearin candles emitted twice as many ultrafine particles as white paraffin, besides higher particle mass. It also found that the particles agglomerated to larger particles, and here again, stearin candles did not fare well. However, one cannot conclude that stearin candles are more harmful without analysing the particles, the study said.
To assess the health risk from these particles, the study used two scenarios — regular and major users. It found that the stearin candle that had the highest discharged particle mass exceeded the WHO’s threshold value for PM 2.5 in case of major users, with steady burning of the candle. However, a candle that burns with a sooty flame causes significantly increased PM2.5 and carbon levels in the air, and under sooty conditions, the threshold values exceeded WHO values in both the user scenarios.
Pointing out that the primary particles from the candles were very small (5-30 nm), the study said, “The deposition and the possible accumulation of these particles in the alveoli (of the lungs) might therefore induce adverse health effects.” However, to come to definite conclusions, there was a need for chemical analysis of the emitted particles.
In the subsequent chemical analysis of the particulate matter released by stearin candles, published by the DEPA in 2018, it was found that almost all particle matter consisted of water soluble salt used for wick protection. The study did not see any health hazard from the soluble salt. Further work is on.
So while we await more conclusive research, we need to play safe and avoid burning candles inside the house. If you are tempted to burn them occasionally and in small numbers, make sure that the wick is cut to a quarter of an inch and the flame is small and steady — a long wick leads to an unsteady and ‘sooting’ flame and higher particle emissions. So also a draught from a window or a fan that leads to flickering or an uneven flame.
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