Dr Saleyha Ahsan “Do you choose the fresh scents of citrus or pine for you cleaning products? Do you use air fresheners or scented plug-ins? Well, we’ve all seen the adverts. Maybe you you should think twice about you cleanliness regime.

So here comes the science. And it might make you think twice. Many of these products contain element which can form formaldehyde which can have serious health implications.

Dangers posed by air-freshener products

First of all, we’ve uncovered some new research that suggests using scented products in our homes could be dangerous.

Dr Saleyha Ahsan Cleanliness
Dr Saleyha Ahsan Cleaning

Because they contain chemicals to give them smells we find so appealing. And it seems those chemicals could be doing us no good at all, so… I want to find out.

How big a problem are they for our health? And what can we do about it?

Hence, the first thing we need to know is, what exactly does using scented products do to the air in our homes?

So, over the next week, we’re going to measure just that. With the help of six families from York, Professor Ally Lewis, an atmospheric chemist, and some rather scary-looking kit that will sample the chemicals in the air.

The air from each house will be analysed. When Ally looks at the levels of chemicals in the different houses, he can immediately see differences.

Cleanliness is next to Poorliness

Three houses have moderate levels of chemicals in the air. And their cleaning habits are similar too. But the Kings and Harrisons are much higher, and we think we know why.

Atmospheric Air Cleanliness Samplers
Atmospheric Samplers

Mr Harrison “We do like using scented candles. We have them on, certainly, daily.”

And then came the Bissell family. They were so high that Ally had to adjust the monitor inside their house. And it turns out they use a lot of cleaning products.

Also, Mrs Bissell says “I keep wiping round all the cupboards and polish the table. I take the dog out four times a day. Then this floor gets washed constantly from mucky feet when he comes in from a walk.”

Dr Saleyha Ahsan “So what exactly are the chemicals that these everyday household products are leaving in the air, after these bouts of cleanliness?”

Chemical Air Analysis
Chemical Air Analysis

Professor Ally Lewis “But you can see the stand-out chemicals here are the big orange ones. This is a chemical called limonene. Limonene has got a very distinctive smell. You can tell by the name. it’s a lemony sort of smell. And it’s used very, very widely to perfume things.”

Dr Saleyha Ahsan “Are they dangerous?”

Professor Alistair Lewis

And Professor Ally Lewis “So, in themselves, almost all of these chemicals are perfectly safe. However, a lot of these compounds are actually quite reactive in the atmosphere, so once you release a compound like limonene, it doesn’t stay as limonene for ever.”

Formaldehyde from Limonene

Because Dr Saleyha Ahsan relates “When it gets into the air, limonene reacts to form a chemical called formaldehyde. And formaldehyde is toxic and even be cancer-causing, so not something we want in our houses. A high price for cleanliness”

Professor Alistair Lewis
Professor Ally Lewis

Professor Ally Lewis “For every two molecules of limonene we put into our home, we form roughly one molecule of formaldehyde as a product.”

Dr Saleyha Ahsan “We’ve measured formaldehyde as well in three of our houses and found that the more limonene they use, the higher their formaldehyde levels. So, do we need to abandon cleanliness and throw out all scented products? Well, we found a hint of an alternative solution, and it comes from NASA.

Faced with the problem of keeping the air inside an enclosed space station chemical free, they tested a homely possibility – house plants. It seems they can absorb chemicals through the pores in their leaves and break them down.

So we’re going to put them to the test here on Earth too. We’re giving our six families some house plants to place around their homes.

Maintaining Normal Cleanliness

They don’t yet know our initial results, so they’re still using all maintaining their normal cleanliness routines with their normal household products.

And, over a four-week period, we’re taking more tests of the levels of limonene and formaldehyde in their homes to see if the plants make a difference.

Finally, we welcome all the families to the local pub… to discover the results.

First we share the baseline level of chemicals we found at the start of the experiment. Rather a shock for the Bissells.”

Household Cleaning Products
Household Cleaning Products

Professor Ally Lewis “House four, the Bissells’ house, holds a world record with us. It’s the highest concentration of limonene we have ever recorded.”

Dr Saleyha Ahsan “So, what happened to these very high limonene levels when we put the plants in? Well, compared with the start of the experiment, it turns out they’re actually higher. But Ally can guess why.”

Professor Ally Lewis “There is a small increase in limonene in most homes and that’s potentially reflecting the fact that we’ve gone into winter and people have begun to seal up their homes – they’ve begun to close windows and doors and make their homes more airtight.”

Houseplants Absorb Harmful Chemicals

Dr Saleyha Ahsan “Just closing windows a bit more, and lighting more candles, have made limonene levels rise. And this should, in turn, cause a rise in toxic formaldehyde as well. But our results show quite the opposite.”

Professor Ally Lewis “What we do see is that the formaldehyde is lower in all the homes after the plants were introduced than before.”


Dr Saleyha Ahsan “In each of the three house in which we measured formaldehyde, over the course of our experiment. the levels fell. it suggests that the plants might really have absorbed formaldehyde.”

Professor Ally Lewis “It is unusual that the limonene has gone up in lots of homes but we haven’t seen that increase in formaldehyde, so I think it’s something worth exploring in the future.”

Hence, Dr Saleyha Ahsan “All our volunteers are now much more aware of what they are using in their houses.

This study has really surprised everyone who’s been involved in it. Just how high our levels of chemical pollution in our houses can be.

And, by our own behaviour, a few simple steps can actually bring that down.

On a slightly different health topic, did you know that there is a peanut allergy treatment.

To find out which plants are best at absorbing chemicals, go to our website… bbc.co.uk/trustme


All of the above information came from the BBC series Trust Me, I’m a Doctor

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