Anyway, where does a candle go when it burns? Is it healthy to breathe in melted candles? How should I be worried?
– Abigail B., Washington, DC
When candles burn, most of their matter is released into the air.
The light and heat from the candle come from burning the wax. When the wick is lit, a fire makes some of the wax melt, flow onto the wick and evaporate, and then the wax vapor burns. The wick, made of cotton, also burns, although the wax contributes most of the heat. Sometimes you will see puddles of water around the base due to the wax pouring out and dripping without burning.
Wax is created from hydrogen and carbon. When the candle burns, the hydrogen and carbon from the wax combine with the oxygen in the air to become carbon dioxide and water vapor. Most of the matter in the candle ends in the form of these two gases.
Carbon dioxide and water are inaccurate safe – too many can be extremely dangerous, as anyone on a submarine can tell you – but on a low level, they are normal parts of the air. The amount of air each candle produces is small – comparable to the amount of gas that someone else in the room exhales.
If the candle burns completely, all molecules from the wax combine with oxygen to become CO₂ or steam, but the candle does not burn completely. Around the edges of the fire, clumps of carbon molecules – perhaps 0.1% of the mass of the candle – were blown away before they finished burning, like chunks of food spewed out by a kitchen mixer. These particles contribute to smoke and soot.
Aneta Wierzbicka, a scientist at Lund University in Sweden who studies indoor air pollution, has conducted several experiments to measure the amount of particle emissions from a candle flame. She told me: “Candles, in non-smoking homes, are one of the strongest sources of seeds in the home, followed by cooking.
Regular exposure to these tiny particles can lead to cardiovascular and respiratory diseases, she said. For those who light candles from time to time, the risk of fire is probably a bigger concern than air pollution. But she says if people burn a lot of candles daily, then steps should be taken to minimize exposure to airborne particles. She suggests that make sure the room is well ventilated and use white, clean candles that don’t have too many additives or ingredients, as everything in the candle will end up in the air. (She also mentioned that electronic candles have been pretty good lately – at first glance, some of them might even fool a candle expert!)
When a candle burns, CO₂ and the water vapor it creates cools and dissolves into room air, indistinguishable from any other CO or water molecules. Over the next few hours, when the air in your room is exchanged for outdoor air, molecules from your candle will escape from the room and begin to diffuse into the atmosphere. After about a year, the atoms from your candle will spread completely across the globe.
In the next few years, every time someone breathes in air, they will breathe a few carbon atoms from wax and a few oxygen atoms from the air in your room.