The truth about your scented candle habit

There are few sensations more instantly soothing than lighting a scented candle. It doesn’t matter whether you’ve chosen a high-end brand or a £4 supermarket dupe with suspiciously similar packaging: this simple act can soften the edges of the most stressful days (and make you feel like you just about have your life together at the same time).

Simply ignite the wick, watch the flame flicker to life, then let your fragrance of choice waft through the room while feeling equal parts smug and sophisticated. Extra points if the scent is designed to evoke some hyper-niche experience, like flicking through old tomes in a vintage bookshop, walking into a bakery on a sunny morning, or perusing a specific flower market at dusk.

For better or worse, they’ve become a shortcut to self-care and a quick fix for our frazzled nerves (plus, they’re the perfect prop for an artful social media post, which certainly hasn’t harmed their popularity). No wonder, then, that these delicately fragranced status symbols have become big business. Between 2021 and 2022, UK shoppers spent £418m on scented candles, according to data analysts at Kantar, and over the next decade, the global market is predicted to rise from almost $4bn to $6.1bn (£4bn). As far as guilty pleasures go, they might seem pretty harmless, bar the staggering price tag that comes attached to some of the fanciest offerings, of course. But do we need to take a closer, more critical look at what exactly it is that we’re burning?

By now, we’re all well aware of the dangers of air pollution, and how the fumes released when we burn fossil fuels can negatively affect both the environment and our health. Over the past few years, though, scientists have become increasingly concerned about the quality of the air inside our homes too. After all, people living in developed countries tend to spend up to 90 per cent of their time inside, so it makes sense to pay attention to what we’re breathing in. Everyday processes such as cooking (and indeed burning candles) can generate particulates and other pollutants, which are risk factors for heart disease, stroke and lung cancer. According to the World Health Organisation (WHO), household air pollution causes more than 3 million deaths each year.

A handful of studies have specifically focused on the impact of burning candles indoors, with some potentially worrying results. In 2017, experiments on mice by researchers at Copenhagen University found that particles released by burning candles caused more damage than the same dose of diesel exhaust fumes. Another Danish study explored exposure to ultrafine particles, which can penetrate deep into the respiratory system and exacerbate lung disease, and found that candle burning was responsible for around 60 per cent of this exposure. Why does so much candle research originate in Denmark, you ask? The Danes are among Europe’s top candle consumers, getting through an average of 6kg per person annually (blame the “hygge” phenomenon, which is all about staying in and getting cosy).

So how concerned do we actually need to be about our favourite little luxury? A candle is “effectively a small combustion source with an open flame”, explains Professor Christian Pfrang, chair of atmospheric sciences at the University of Birmingham. Much like a fireplace, gas hob or wood burning stove, he says, it will produce nitrogen oxides, carbon dioxide and carbon monoxide, especially if combustion is incomplete. In case it’s been a while since your science GCSE days, incomplete combustion takes place when you burn something without a sufficient oxygen supply; sooty deposits around the top of your candle’s jar are a telltale sign of this. “Nitrogen oxides and carbon monoxide are known to have major health impacts,” Pfrang adds, including lung and heart problems. But, he cautions, experiments tend to show that the levels released by a single candle are unlikely to exceed the amounts set out in the WHO guidelines on indoor pollutants.

Particulate matter, explored in the aforementioned Danish study, is another important piece of the puzzle. Burning a candle will produce “particles of different sizes, with small particles [known as] PM2.5 and ultrafine particles being of most concern”, Pfrang says. Exposure to PM2.5 has been shown to most strongly affect elderly people with chronic heart and lung disease, children and asthmatics, he adds.

And new research is starting to explore the potential impact on the way our brains work, too. Earlier this year, Pfrang’s colleagues at the University of Birmingham, along with scientists at the University of Manchester, found that an hour’s exposure to a burning candle impaired our cognitive function, diminishing the participants’ ability to focus and to interpret the emotions on other people’s faces.

When you start to put fragrances into the mix, things become more complex. Burning any type of candle produces volatile organic compounds (VOC), which evaporate easily and are released as gases. In this context, “the word ‘volatile’ basically means something that is easily going to go into the air”, says Nicola Carslaw, professor of indoor air chemistry at the University of York. Additional artificial smells mean more VOCs.

Other scented products – take perfume, for example – will also contain VOCs. But the difference is in how we use them. We don’t tend to, erm, burn perfume, but when we strike up a candle, the VOCs “will interact with combustion products in the flame, so [they] are potentially more harmful”, Pfrang says. Formaldehyde, benzene and toluene are just some of the toxic VOCs released when you light up. “Some of the VOCs released can exceed WHO recommended values,” says Pfrang, who singles out acrolein and benzo[a]pyrene as being “of particular concern, as they are associated with various diseases, including cancer”.

Aroma chemicals crop up in everything from air fresheners to cleaning products to shower gels, Carslaw says, “and the problem is that they are quite reactive once they’re released”. Research has found, she adds, that more particles are made when these chemicals oxidise in the air. Recent studies from Purdue University in the United States, for example, have found that these airborne pollutants are small enough to penetrate deep into the lungs.

If all this has you ready to throw your prized candles in the bin, artisan jars and all, then hold fire. The good news is that by making a few swaps, and by changing the way you use them, you can carry on indulging without worrying too much. The first thing to do is to think carefully about air flow. “Ventilation is key to removing indoor pollutants from your home,” says Pfrang. “This is most quickly achieved through cross-ventilation, when you create a draft for a short time by opening multiple windows.” It might sound like stating the obvious, but how many times have you been guilty of firing up, say, a cinnamon-y Christmas-themed candle in the depths of winter, while keeping your home hermetically sealed to stay as warm as possible? (once again, I blame hygge).

Proper ventilation shouldn’t negate the candle’s smell, either. In fact, it should help the fragrance circulate properly, by maximising the “candle throw” (an insider term for how well the scent moves around a room).

While the odd candle isn’t going to make you “keel over and collapse”, as Carslaw puts it, the quest of “where you burn” is important too. “You quite often see it in big Hollywood movies: there’s something in a room with 20 scented candles around them, in some sort of romantic scene. If you start doing that sort of thing in a very poorly ventilated area, that’s when you’re going to get problems.” So, essentially, don’t try and recreate Monica and Chandler’s proposal scene from Friends. And even though scented candles are often sold to us as a crucial part of any wind-down routine, she cautions against lighting them in smaller spaces such as a bathroom, or burning one for extended periods in your bedroom before you go to sleep.

And as tempting as bargain dupes with similar scents might be (they’re basically the fragrance equivalent of a fast-fashion brand’s rendering of a designer dress), it’s worth getting to grips with candle ingredients too. “You absolutely get what you pay for,” explains Gail Race, an interior designer who has previously worked in product development for home fragrances. Cheaper candles, she says, “tend to be [made from] paraffin wax with an artificial fragrance” (even if that fragrance is something that sounds like it could have been naturally derived – a cut-price brand will tend to use, say, artificial lavender scents rather than sourcing the real deal).

Burning paraffin, which is derived from oil, releases potentially dangerous chemicals. “As you go up the price bracket, people are using much cleaner-burning waxes like beeswax and coconut,” Race says. These also happen to be more eco-friendly options, too. She also recommends taking a closer look at the wick, which sometimes gets overlooked when we’re getting over-excited about niche fragrances and aesthetic packaging. Once, wicks were made with a lead core to keep them standing upright, but these were banned in 2003 due to safety concerns (worth bearing in mind if you end up digging out any ancient candles for nostalgia purposes). Cotton or wooden wicks tend to be a safe, sustainable choice.

It’s worth bearing in mind, too, that “when the candle is extinguished, it can produce a large burst of particles”, Pfrang says. So, the moment that you blow out the flame is actually “the most polluting aspect of candle use indoors”. He recommends using a candle snuffer instead: this might sound Dickensian, but it’s just a simple device that extinguishes a flame safely and cleanly. You can buy aesthetically pleasing ones from posh interior design brands and lean into the object d’art of it all or you can opt for a simple one from, say, Ikea for £1.50.

Essentially, Pfrang says, we don’t need to stress too much about “occasionally using a candle”, but it is important to be aware of the potential pollutant risk, so that you can “minimise exposure while [still] enjoying what you like to do”. You’ll find me lighting up a Diptyque “Baies” in celebration. With the windows open, of course.