Have you ever thought about what happens when you light a scented candle? How about when you randomly cook a bacon sandwich at an ungodly hour, and within a minute or two, you’re wading through a thick haze of smoke and trying to crank open a window so you don’t suffocate your flatmates?
Think about the times you’ve suddenly had the urge to do a purge-clean and spray down every single surface in your student house because grime has accumulated over months now and is unbearable. What’s going on…chemically?
Despite spending over 90% of our time indoors in developed countries like the UK, few of us have ever given any thought to the idea of indoor air pollution, and the impact our activities inside are having on our health. Much of the focus is placed on the outside world (i.e. car exhausts, power stations, and conspiracies about aeroplane vapour trails).
“There’s far less awareness. People don’t tend to do anything about it, because they don’t know.” These are the words of Nicola (Nic) Carslaw. Nic is a professor of Indoor Air Chemistry at the University of York’s Department of Environment and Geography. With her team, she has recently received a £2.9 million research grant to study the effects of indoor air pollution.
So, what is indoor air pollution? Well, as you’ve probably guessed, it’s all the air pollution we’re generating inside our homes, offices, and other buildings. From lighting scented candles and frying food in our kitchens, to using disinfectant sprays and perfumes.
“Many of the pollutants we generate in our homes like nitrogen dioxide (NO2) and Particulate Matter (PM) are the same pollutants generated outdoors. There are similar processes going on. For instance, gas cooking involves the process of combustion, which is the same process as a car engine.”
So, frying bacon on the stove could be damaging our health as much as inhaling exhaust fumes from a car?
“It’s interesting, when you cook with gas, you are producing NO2 – that is the same pollutant that a typical car engine produces. It doesn’t matter if you’re exposed to it indoors or outdoors – a unit of concentration of NO2 will do the same damage to you whether you make it indoors or out.”
But, Nic says, it’s not that simple, as NO2 is not the only pollutant produced by cars, or cooking. “It gets more complex when looking at the PM. These are tiny particles scientists worry about because they can get right down into your lungs and into your respiratory system. We know cars generate those, and cooking generates those too. But with cooking, the composition is very different, and scientists don’t really know if diesel-generated particles are more harmful than cooking-generated ones. The research hasn’t been done.”
How about scented candles, what’s going on there?
“Scented candles, cleaning products, shower gels, perfumes, and aftershaves – these all have fragrance chemicals in them.” These include common chemicals you may have heard of such as linalool and limonene. If you haven’t heard of these, check the back of a perfume bottle or disinfectant spray and you’ll likely find them.
“They have a pleasant aroma, that’s why people buy them, they want to smell nice, they want their homes to smell nice. The thing is, those chemicals are very reactive once released into the air.”
When you light your scented candle, fragrance chemicals are released and can react with oxidants in the air, making particles that are bad for your health, as well as other pollutants like formaldehyde. Formaldehyde is a known carcinogen, meaning it can cause serious breathing problems and even cancer when present at high concentrations.
It’s not just frying food, or lighting candles though, Nic says indoor air pollution can also come from sources you wouldn’t expect.
“Quite often furniture is glued together, and some of the chemicals used for painting, varnishing or whatever, will off-gas.”
In other words, your brand new sofa may release chemicals into the air of your home as soon as you unwrap it, and the thing is, not enough research has been done into the short-term or long-term impact this could be having on your health.
So, what can we do to reduce air pollution inside?
“My buzzwords are education, moderation and ventilation. You need to know about it to do something about it.” Reading this article is a good start.
“When I talk about moderation I mean not obsessively cleaning, not having twenty scented candles in a small room. There are lots of sources of pollution, and in themselves, they are probably not that bad for you, but if you use a lot of those things in a small, badly ventilated space, you could be doing yourself some harm.”
Nic recommends getting to know what sources of air pollution are inside your home, and moderating them (i.e. cutting down on scented candles, reducing the amount of food you’re frying, and using things like cream cleaners instead of disinfectant sprays).
The third thing is big: ventilation. “In the vast majority of cases, unless you live on a busy road, just open the window. Even if you do, open the window on a different side of the house, away from the road. Just ten minutes after you cook, or for half an hour every day, and you’re probably going to let out most of the emissions you generate in your home.”
Nic also recommends switching to an electric or induction hob, or making sure you have an extractor fan on while you’re frying. Even cooking food on the back rings of your stove with the fan on can reduce the pollutants spreading in your kitchen.
“A lot of it is about knowing – knowing it’s a thing. I teach students in Environment and Geography, and when I teach them about indoor air quality, none of them have ever heard about it before – it’s just not on the curriculum, it’s not on the radar. When they’re taught at school in Chemistry, it’s all about outdoor air quality.”
So, it turns out, indoor air pollution is a very real thing – and perhaps reading this will make you think twice about lighting your twenty scented candles or doing a deep clean of your home as if it’s a crime scene. Maybe, just, go easy, and crack open a window when you fry your bacon, or go veggie.
Nicola Carslaw is a professor of Indoor Air Chemistry at the University of York.
You can find out more about her research on the York Research Database.
Many thanks to Nic for giving her time for this article.