Most of us are aware of the health effects of combustion by-products from major outdoor sources, such as cars and power plants, and even from obvious indoor sources such as stoves. Few are aware of the potential health effects of regularly burning candles – even though these are usually lit indoors, in small, poorly ventilated spaces.
In research by the US Environmental Protection Agency and the American Lung Association, candles have been shown to emit a frightening range of carcinogenic volatile organic compounds (VOCs), including acetone, acetaldehyde, benzene, carbon disulfide, carbon tetrachloride, chlorobenzene carbon monoxide, creosol, cyclopentene, ethylbenzene, formaldehyde, phenol, styrene tetrachloroethene, toluene, trichloroethene and xylene.
In addition, like anything that burns, candles produce a microscopic soot that can sometimes contain toxic heavy metals released from the candle wick.
The purpose of a candle wick is to draw wax to fuel the candle’s flame. Generally speaking two different types of wick are used: cored and non-cored.
Non-cored wicks are generally made of a braided or twisted fibre (usually cotton), and are considered the safest to burn. Cored wicks also use cotton, but this is wrapped around a paper or metal core to give it support. Wicks with a metal core also burn at a higher temperature, useful when the candle is made of a wax that only melts at high temperatures. Lead and cadmium are the most common metals found in cored wicks, but zinc and tin can also be used.
As the candle burns, it releases dirty soot containing sub-micron-sized particles light enough to remain suspended in the air for considerable time, and small enough easily to be absorbed into the body once inhaled.
Research by the Environmental Protection Agency (EPA) has shown that burning multiple candles, or a candle with multiple wicks, can lead to high levels of indoor pollution. Scented candles give off more of this soot than unscented candles.
The problem of candle soot was illustrated in a 2000 study at the University of Michigan School of Public Health. Researchers there examined a range of candles made in the US, Mexico and China, and measured the amount of lead they emitted while burning, as well as the amounts left in the air in an enclosed space after one hour and five hours.
Results showed that lead emission rates for the candles ranged between 0.5 and 327 micrograms (mcg) per hour. After burning the candle for one hour, the lead levels in the air ranged from 0.04 to 13.1 mcg per cubic meter (‘safe’ levels, as defined by the US Environmental Protection Agency are 1.5 mcg per cubic meter); after five hours they were 0.21 to 65.3 mcg per cubic meter.
More recently, in 2006, atmospheric scientist Stephan Weber of the University of Duisburg-Essen, in Essen, Germany, measured levels of micro-particles in the air of a single church over a 13-day period leading up to Christmas. His equipment measured concentrations of particles up to 10 microns (ìm) in diameter (PM10) and also those 1 ìm in diameter or smaller (PM1). The church used both candles and incense during its services, and Weber found that concentrations of both types of particle almost doubled when just candles were burned. Burning candles and incense together raised the concentration of PM10 to levels seven times those recorded between services, and PM1 to about nine times background levels.
Concentrations of particulate matter quickly dropped after the candles were extinguished, but remained elevated for 24 hours after simultaneous use of candles and incense.
Weber concluded that even brief exposure to contaminated air during a religious service could be harmful to some people.
Two years earlier, researchers in the Netherlands also measured particulate matter in churches that burn candles. Theo de Kok, of Maastricht University, found that when candles had been burning in a Dutch chapel for nine hours, particles in the air there formed 10 times as many free radicals as airborne particulates collected along busy roadways travelled by 45,000 vehicles daily. It also had levels of tiny solid pollutants (PM10s) up to 20 times European limits.
According to De Kok, PM10 from candles might be especially harmful because, in the body, constituents of the smoke readily generate free radicals that damage cells.
Around the same time, the UK consumer magazine Proof! reported on its laboratory analysis of a range of pillar-type candles and tealights purchased from supermarkets, department and home furnishing stores in London. The smoke from the burning candles was analysed for traces of lead and cadmium. Seventeen per cent (or nearly two in 10) had detectable levels of cadmium and a small number also contained lead, though levels detected were also well below those found in other surveys. In this analysis, the candles with the most lead and cadmium were scented candles purchased at Boots. Other cadmium-containing candles came from IKEA. In common with other data, the survey found that metal-containing candles came from China, as well as Poland and Germany.
In April 2003, the Consumer Product Safety Commission banned candles with lead wicks from being imported to or sold in the US. Other countries, including the UK, have yet to follow suit. There is no way to distinguish lead-containing wicks from safe ones, nor do labels state what a wick contains.
Apart from how its wick is made, how ‘cleanly’ a candle burns depends on several other factors, including the type of wax it is made of, whether it is perfumed and coloured, and how long the wick is. A wick that is too large will flare and produce more soot than a properly trimmed one; and a flaring smoky flame will put particulate matter into the air no matter what the wick is made from.
Tallow and other unprocessed animal fat, once widely used in candle-making, are no longer popular. Instead, paraffin, which is made from petroleum waste, is the most common type of candle wax. From the manufacturers’ point of view it is cheap and easy to work, has an appealing translucence and is slow-burning. Stearic acid (a component of tallow and some vegetable fats) is commonly added to paraffin candles to raise their melting point and burning time.
Gel waxes, popular because of their crystal clarity and ability to hold colour and fragrance, are basically petroleum oil turned to jelly, and need to be used in a container (often with a reinforced wick) because the wax is very soft. Both types produce smoke and soot.
It can be hard to make a candle using natural essential oils. Good-quality essential oils are expensive and so are not suitable for production-line candles; they also may not blend well with candle wax. They can be more volatile than synthetics and difficult to use in candles unless they have added stabilisers or fixatives.
So manufacturers generally use more toxic synthetic fragrances. In addition to these, many types of candles contain synthetic colours. The safety of colours used in candles depends largely on the ingredients of the dye, but most synthetic dyes will give off some unsafe particles on burning.
It is almost impossible for most consumers to tell the difference between candles with metal-containing wicks and those that are metal-free. You may wish to avoid candles made in countries such as China – though many candles on the market contain no labelling information to say what they’re made of or where they’re made. Likewise, few candles will provide information on fragrance ingredients or types of wick (indeed, this is not required). A legal requirement for clearer labelling would certainly help consumers make better choices.
What’s in candles?
Candles contain a complex mix of unseen and unlabelled ingredients that add to the atmospheric pollution they create. Emissions include:
Even low levels can adversely affect the central nervous system (brain and spinal cord), the heart, red blood cells and kidneys. Chronic exposure in adults is associated with endocrine and reproductive problems. Lead exposure in children is linked to behavioural problems and depressed intelligence.
Inhaled cadmium is carcinogenic. Overload can cause yellow teeth, dry skin, chronic bronchitis and fatigue. Toxic to liver, kidneys, bones and testes, as well as disruptive to the immune, hormone and cardiovascular systems.
Synthetic perfumes contain toxins and sensitisers capable of causing cancer, birth defects and central nervous system disorders. Other toxic effects include asthma, allergies and skin disorders.
Polycyclic Aromatic Hydrocarbons
When volatile chemicals are burned they release PAHs, which are absorbed through the skin as well as inhaled, causing skin, eye and respiratory irritation, nausea and headache. Long-term PAH exposure can cause cancer, central and peripheral nervous system damage, and hormone disruption.
Microscopic particles (10 microns or less in diameter) are easily and deeply inhaled into the lungs, and can damage the heart, lungs and arteries, as well as cause respiratory problems and trigger allergies. Long-term exposure increases the risk of death from heart disease.
This article first appeared in the Ecologist February 2008