This short note is heavily based on Are Ions Good for You, a beautiful exposition of the actual science of ionisation and pollution of the air.
There are lots of claims around the internet, mostly by beeswax candle makers, that beeswax candles are “natural ionizers”. The theory goes that beeswax candles emit “negative ionisation” which spreads through the room and causes pollutants and allergens to bind together because, apparently, those things are positively charged. No source or explanation is ever provided, and I very much believe that’s because the claim is bogus.
First of all, one of the most fundamental tenets of the laws of physics is conservation of charge. The creation of every negatively charged ion must be accompanied by the corresponding creation of a positively charged ion. If the candle is producing just negative ions, where are all these positive ions going? They’re either being emitted as well (thus completely defeating the purpose of increasing the ratio of negative charges in the air) or the candle itself is going to end up with an enormous positive charge (which will attract and neutralise any negative ions in the air, again defeating the purpose). It’s just impossible for a candle to simply release negatively charged ions and have that be the end of the story. End of story.
OK, so let’s just assume, for the sake of argument, that candle do somehow add negative ions to the atmosphere. Is this good? According to a series of papers published by Krueger et al. between 1957 and 1963, negative ions help the airways in the lungs to clear. However, in 1971, Andersen’s book Mucociliary Function in Trachea Exposed to Ionized and Non-Ionized Air proved these claims to be false. Not only did he carefully identify the flaws in the earlier studies, he performed a large experimental study under very controlled conditions that demonstrated that there is no relationship between ion concentration/polarity and the performance of the airways of the lungs. Despite the earlier papers being debunked, they are still referenced to this day in a show of stunning confirmation bias.
It gets worse. New ion pairs (that is, one negative and one positive) are created in the air continuously due to radioactive decay and cosmic radiation, at a rate of 5–10 ion pairs per cubic centimeter per second. These ions are continuously recombining, as they are attracted due to the opposite charges. A high level of pollution will turn most of the ions into charged particles, or heavy ions, but with no preference for either polarity. Since the 1930s, it has been known that the attachment coefficients for negative and positive ions attaching with aerosol particles are almost the same, resulting in a population of aerosol particles divided more or less equally between negative, positive, and neutral particles. This is true with moderate pollution levels. With very high aerosol concentrations, there are not enough ions to charge the aerosol particles, and the neutral particles will dominate.
Again, this measured, controlled science completely conflicts with the claims on the beeswax store pages. Where does this claim that all the pollutants are positively charged come from? How does that claim even make sense?
It’s worth noting that hot flames do create ionisation, albeit balanced positive and negative charges (as demanded by basic physics). This only happens to an appreciable extent in flames over 1500°C; candle flames are closer to 1100°. Furthermore, the ions rapidly recombine as they leave the flame, there’s no way the candle in the corner of the room can have a significant effect on the constant generation and recombination of ions happening in the rest of the room.
Also, in defence of candles, they are little miniature incinerators that draw fresh, possibly dusty and polluted air up into the flame. It stands to reason that these pollutants will be turned into harmless CO2 and H2O. But I’ve failed to find any evidence that this effect has any noticeable effect on pollution levels, nor any explanation why beeswax candles would be particularly good at this. Surely if this were true, there would be scientific papers confirming this, and the beeswax candle makers would be the first to proudly reference this research. These claims are much easier to test than the ionisation claims. But instead, they implicitly reference papers from the 1950s that have been well and truly debunked and disproven.
I’ve nothing against beeswax candles themselves. If you buy locally sourced beeswax candles, you’re going to get something that smells nice, (apparently) lasts much longer, doesn’t have a huge ecological cost, and your money is going to a beekeeper instead of an overseas petrochemical conglomerate. Heck, they’re even sustainable probably. All of these plus points make it all the more puzzling that they overreach to these absurd ionisation claims.
Extraordinary claims demands extraordinary evidence. The online stores that expound upon the beeswax candle’s special ionisation properties are all extraordinary claim and zero extraordinary evidence.
Have I missed something? Do you think it might be possible that beeswax candles have special ionisation properties? Have you got evidence? Let me know what you think in the comments below.