Exposure to cleaning products and childhood asthma: more than just a link?

KEYWORDS:

• Cleaning products
• volatile organic compounds
• childhood asthma
• precautionary principle
• regulation

1. Introduction

Sustained exposure to cleaning products can cause airway irritation and chronic inflammation, triggering asthma symptoms and worsening asthma control [1]. The link between cleaning product use and worsened respiratory health is largely based on occupational exposure in adults. Recent cohort studies show that these risks are not exclusive to workers, and that household exposures carry risk for the development of airways disease in young children as well. Young children spend at least 80–90% of their time indoors, have an increased respiration rate, hand-to-mouth behaviors, breath closer to the ground where airborne concentrations of the ingredients are higher, and are still developing their immune and respiratory systems [8,9]. This makes them especially vulnerable and reinforces the need to identify modifiable risk factors of asthma in early life.

In the UK, the ALSPAC study found the frequent use of chemical cleaning products during pregnancy was associated with persistent wheeze in children [5], and that a maternal composite household chemical exposure score was positively associated with early and intermediate persistent, and late-onset wheezing in children who were not atopic [6,10]. A recent study from a Canadian birth cohort found an increased frequency of household cleaning product use measured at 3-months of age to be associated with an increased risk of developing asthma and recurrent wheeze in early childhood [7]. A Dutch study of adolescents found living in a home with higher cleaning product use was not associated with asthma, rhinitis, or eczema risk, differing from the previous studies by focussing on an age group with a more developed and therefore less sensitive respiratory and immune system when compared to children and infants [11].

2. Common contents of cleaning products

The products ingredients and their delivery mechanism appear to be important determinants of risk from cleaning products, particularly liquid or solid air fresheners, spray air fresheners, plug-in deodorizers, dusting spray, glass cleaners, anti-microbial hand sanitizers, and oven cleaners [7]. Many of these products have been previously identified in occupational studies be associated with increased risk for asthma [1,2,12]. Sprays, scents, and disinfectants are three product groupings that we will examine here.

2.1. Sprays

It’s not just what chemicals are in a product, but how it’s applied that creates the hazard. Spray and aerosolized cleaners have been noted for their potential for risk by many studies. Their spray mechanism, pump or trigger, is convenient for users but facilitates aerosolized exposure. The frequency of use or number of cleaning sprays has a dose-response relationship with airways disease [1,3]. Plug-in air fresheners may be particularly hazardous because they emit terpenoids, phthalates and other irritants at a continuous rate, creating chronic exposure [13].

2.2. Scents and volatile organic compounds

Many fragranced cleaning products contain volatile organic compounds (VOCs) [14,15]. One study of 25 common fragranced consumer products identified 133 VOCs, and an average of 17 VOCs per fragranced product, only one of which was listed on ingredient labels [14]. VOCs are highly reactive and when mixed with ozone or other common chemical cleaning products can create secondary pollutants [16]. With more than 100 different VOCs identified in field studies of household cleaning products [14,17], the extent that secondary exposures are created when common cleaning products mix is not fully understood and remains a challenge for researchers [18]. Common fragrance ingredients include terpenes such as limonene or linalool, and phthalates.

Current disclosure regulations allow ingredient labeling that lacks transparency, and the moral right for consumers to know what they purchase. ‘Fragrance’, or its other vague connotations (i.e. parfum, organic fragrance, pure fragrance), can refer to a single chemical or combination of hundreds of compounds, and as proprietary ingredients or trade secrets do not need to be disclosed on an ingredient label [14]. Furthermore, products that claim to be unscented may include fragrances and/or masking agents [14].

While fragrance exposure alone have not been linked to asthma development, likely due to the ambiguity and ubiquity of their presence in everyday consumer products, some have been linked to asthma exacerbation, atopic dermatitis, and contact allergy [14,19]. Air fresheners, deodorizers, hand sanitizers, floor cleaners, and scented laundry detergents are all products that often contain fragrance and volatile organic compounds [13,14], and that were found to have an association with the development of a childhood recurrent wheeze, allergy, or asthma [7]. Detergents, disinfectants, polishes and all-purpose glass and surface cleaners also contain many compounds that irritate and inflame the airways [15].

2.3. Disinfectants

Chlorine bleach is the most commonly used disinfecting and cleaning agent in the developed world, as it is easy to use, low cost, can deodorize, and kills a wide range of microorganisms. The common active ingredients in disinfectants, quaternary ammonium compounds (QAC’s) and sodium hypochlorite (bleach), have been linked to reduced airways function, irritation and sensitization in young adults [1,2,7]. Similarly, frequent use of antimicrobial hand sanitizer as a disinfectant is associated with an increased odds of recurrent wheeze, recurrent wheeze with atopy, and asthma diagnosis [7]. Flu season or a viral pandemic such as COVID-19 exemplify times when the benefit of disinfectant use outweigh its risks. However, the frequent application of disinfectants may not be warranted in business-as-usual settings.

3. Potential mechanisms

As a complex disease, asthma is caused by a combination of environmental and genetic factors. In irritant-induced asthma, household cleaning products target the respiratory epithelium, causing bronchial hyper-responsiveness and wheeze as a result of chronic exposure [6]. Cleaning agents have been found to directly disrupt the barrier functionality of human bronchial epithelial cells, even in dilute concentrations [20]. Over time, this damage worsens, causing remodeling, reduced lung function, increased airway reactivity, and heightened sensitivity to future exposures. A compromised epithelial barrier increases a child’s vulnerability to viral infections, irritation or inflammation, and acquired immune response to future allergens. Many cleaning products also contain allergenic compounds which can increase sensitivity, particularly when exposed to an already-damaged epithelium.

Early-life exposure to cleaning products appears to cause irritant-induced asthma and chronic inflammation, but not allergy. The chemicals in cleaning products may work primarily through an innate immune response rather than an allergic one, damaging the respiratory epithelium and stimulating inflammation and hypersensitivity to subsequent irritants. This mechanism is consistent with several studies showing no association between atopy and cleaning product exposure [6,7,12].

Another important mechanism to consider involves the child’s microbiome. While the importance of the gut microbiota to human health is becoming clearer, our understanding is limited. A dysbiosis of a child’s microbiome has already been linked to the delivery method, antibiotic use in utero or early life, and whether the subject is breastfed or formula-fed, suggesting sensitivity to environmental exposures [21]. Disinfectants have been found to alter the composition of a child’s developing microbiome by limiting species diversity [22], with reduced diversity in early life linked to an increased risk of developing childhood asthma [23].

4. Challenges, and recommendations

Our efforts to achieve hygienic indoor environments and protect ourselves from pathogens do not come without risk. Cleaning products contain a myriad of irritating and sensitizing chemical compounds, which are often undisclosed making it difficult to protect consumers. While further, focussed research is needed to confirm causality, current findings suggest a cautious approach to the heavy use of cleaning products in the home, particularly where small children are present. A lack of specific exposure information remains a challenge for researchers. When mixed or exposed to ozone, resulting secondary pollutants (e.g. formaldehyde) can cause accidental poisoning and increase the risk of asthma and reactive airway disease [12,13,15,17], adding to concern. With the dizzying array of chemical cleaning products on the market and formulations shifting without consumer knowledge, a precautionary approach for chemical cleaning product use is reasonable.

5. Expert opinion

The link between asthma and cleaning products are highly suggestive, though more studies are needed to confirm a causal link and precisely explain the mechanism(s) of risk. The inconsistency on exposures measures for household cleaning products is further hampered by a lack of transparency in product labeling. A lack of information and weak disclosure regulation results in uninformed and misinformed consumers. Market greenwashing leads people to believe their products are more natural and unharmful, but the products are often found to contain just as many harmful compounds as their non-greenwashed counterparts [14]. As a largely unregulated industry, producers of cleaning products have relatively little incentive to complete pre-market testing, and disclosure of ingredients. When ingredients are disclosed, the hazards are often obscured using vague names such as corrosives, fragrance, or stabilizer.

Intervention trials with more specific clinical and exposure assessments tools (e.g. methacholine challenge and biomarkers) and diverse populations are needed. Future assessments could include evaluation of gut, lung and indoor environment microbiome specific immune response. In the interim, a precautionary approach to cleaning product exposure is reasonable to modify childhood asthma risk. Such an approach forces questions about the necessity of frequent use of these products. Prudent use that balances targeted hygiene with the risks that accompany the use of many cleaners is recommended. To minimize exposure when hazardous products do need to be used, avoid cleaning around children, preventively implement ventilation during and for hours following cleaning activities, avoid mixing products, using dilute concentrations, and remove cleaning supplies from an area promptly following their use [13].

Shifting the responsibility of product safety from consumers to producers is necessary and achievable. Current tools such as the U.S. Healthy Cleaning Product Guide and Canadian Consumer Ingredient Communication Initiative are helpful, but they require informed consumers to seek out information that should be available at the point of purchase. The EU’s REACH program puts the burden of proving chemical safety rightfully on producers before marketing; a better way to manage and communicate environmental health risks to public and a step in the right direction from North America’s current management of household chemicals in consumer products [24].

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Acknowledgments

The views expressed are those of the author(s) and not necessarily those of Simon Fraser University.

Additional information

Funding

This paper was not funded. J Parks has received graduate student research award funding from Asthma-Canada and AllerGen NCE, as well as graduate scholarships from Simon Fraser University in the course of her graduate career.