“Giving your house a weekly clean could be enough to give you asthma”, the BBC News website reported. A Spanish study has found that the weekly use of cleaning sprays and air fresheners is enough to increase the risk of asthma in adults. The report continues by saying that although a link has already been made between using such products and occupational asthma, this latest research suggests that “occasional use in the home also poses a threat”.
The news service also quoted Victoria King of Asthma UK, who said: "We know that up to 25% of people exposed to chemicals, including cleaning sprays, at work will go on to develop occupational asthma.”
This study highlights a potential link between cleaning sprays and asthma symptoms. However, limitations in how the data were collected mean that we cannot say for sure that the occasional use of spray cleaning products causes asthma. At present, sensible precautions such as using these products in well-ventilated areas would do no harm.
Where did the story come from?
Dr Jan-Paul Zock and colleagues from universities and research centres in Spain, the UK, other European countries, and Canada, carried out this research. The study was funded by the US National Institutes of Health and the Carlos III Health Institute of the Spanish Ministry for Health and Consumption. The study was published in the peer-reviewed medical journal the American Journal of Respiratory and Critical Care Medicine.
What kind of scientific study was this?
This was an analysis of data collected in the European Community Respiratory Health Survey (ECRHS), a cohort study of adults aged 20 to 44 years old in 10 European countries.
The researchers identified 3,503 people who did not have asthma or wheezing when they enrolled in the ECRHS study. Nine years (on average) after they enrolled, the participants had a face-to-face interview, during which their use of cleaning products and whether they had developed asthma or asthmatic symptoms was assessed.
They were asked how frequently they had used 15 household cleaning and washing products during the preceding nine years and were given options of: never, less than one day a week, one to three days a week, or four to seven days a week. The products assessed included washing powders, liquid cleaning products (including bleach and ammonia), and spray cleaning products (including air fresheners, furniture sprays, and glass cleaning sprays).
They also asked participants if they currently had asthma (defined as having had an asthma attack, or shortness of breath at night, or using asthma medication in the past 12 months), or wheeze (wheezing or whistling of the chest in the past 12 months, that was not associated with a cold).
If participants reported ever having had asthma, they were asked whether this had been confirmed by a doctor, and how old they were when they first had an asthma attack. Participants who reported having asthma had some clinical tests to investigate how well their lungs functioned, and whether they were allergic to common allergens.
The researchers in this study compared people who had never used each product, or had used them less than once a week to the people who used them more frequently, to look at whether the use of any of the cleaning products during the nine-year period was associated with the risk of current asthma. These comparisons took into account possible imbalances between participants in factors that might influence the risk of asthma, such as smoking, age, gender, where they lived, and whether they had a cleaning job.
What were the results of the study?
The researchers found that about six in every 100 participants had asthma symptoms at follow up, but only about two in every 1,000 participants had had a diagnosis of asthma confirmed by a doctor.
The more people used the sprays, the more their risk of having symptoms, being diagnosed with asthma or using asthma medication increased. These risks were associated with products such as furniture, glass cleaning, or air freshener sprays. Cleaning products that were not in spray form did not increase the risk of asthma.
People who used cleaning sprays at least once a week, were about 50% more likely to have had asthma symptoms over the last 12 months, and 40% more likely to have wheezing, than those who used them less frequently.
People who used sprays at least four days a week were about twice as likely to be diagnosed with asthma by a doctor as those who used them less frequently.
What interpretations did the researchers draw from these results?
The researchers concluded that frequent use of household cleaning sprays increases adults’ risk of developing asthma.
What does the NHS Knowledge Service make of this study?
This study is a relatively large study, but it does have its limitations.
- The main limitation is that the use of cleaning products and the onset of asthma were both assessed at the same time (at the nine year follow up). Because of this, it is difficult to be absolutely certain that the use of these products came before a person developed asthma symptoms. We would need to be certain that use of cleaning products preceded the onset of asthma before we could conclude that they might be causing the symptoms.
- The participants were asked how much they had used cleaning products over an average period of nine years, and their actual use of cleaning products was not verified in any way. Therefore, it is likely that there will be some inaccuracy in these reports.
- It is possible that the people who developed asthma may already have had an idea that the use of cleaning products could be related to their symptoms, and this could have influenced how likely they were to report a more frequent use of cleaning products. The authors of the paper feel that this was unlikely, as data were collected before the potential link between aerosol products and asthma was first widely publicised.
- Another important limitation of this study, were the definitions that were used to classify someone as having asthmatic symptoms. The researchers classified participants as having current asthma if they had an ”attack of asthma and/or nocturnal attack of shortness of breath, and/or current asthma medication in the past 12 months”. Such a classification is likely to cause considerable inaccuracy, as we are not sure what they considered to be an “asthma attack” (particularly as those with wheeze – the main feature of an asthma attack - are grouped separately) Many other medical conditions can cause shortness of breath at night and “asthma medications” can also be taken for other medical conditions (such as obstructive airways disease).
- Although the authors reported that some lung function tests were carried out on participants, they did not report whether these were used to confirm diagnoses or exclude the possibility of asthma in people who did not report having asthma symptoms. If the diagnosis of asthma relied solely on participants’ reports, there could have been some misdiagnoses, as well as missed diagnoses.
- Analysis of the results from the interviews found that asthma symptoms and wheezing were associated with one day a week, or more, of using the products However, a physician confirmed diagnosis was only associated with more frequent usage – of four to seven times a week.
This study does highlight a potential link between the use of cleaning sprays and asthma symptoms. Before we can draw any firm conclusions, we need further studies that clearly establish a consecutive pattern between using cleaning sprays and developing asthma symptoms, and that also objectively measure these symptoms.
Sir Muir Gray adds...
We should avoid as many chemicals as possible, particularly if sensitive to one or more. If you can smell something you are smelling a chemical.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The BBC, 12 October 2007
Links to the science
Am J Respir Crit Care Med 2007. [Published ahead of print on June 21, 2007]