Minimizing indoor allergen exposure: What works?

Abstract

Purpose of Review:

Allergic rhinitis and asthma morbidity has been linked to indoor allergen exposure. Common indoor allergens include dust mites, cats, dogs, rodents, and cockroaches. These allergens are ubiquitous and often difficult to remove from the home, making long-lasting reduction strategies difficult to achieve. Identifying strategies for reducing the presence of indoor allergens in homes could be utilized to decrease allergic disease burden, improve symptomology, reduce healthcare costs, and improve patients’ quality of life.

Recent Findings:

Studies have yielded mixed results with regard to specific environmental control measures in reducing indoor allergen levels and in improving clinical outcomes of allergic disease.

Summary:

In this review, we assess the available evidence of the effectiveness of environmental control measures in reducing indoor allergens and the potential clinical impact of these measures.

INTRODUCTION:

Allergic diseases, including asthma and allergic rhinitis, are common, with asthma affecting nearly 10% of the United States (US) population (1) and allergic rhinitis (AR) having an estimated global prevalence between 10 and 40% (2). Patients with uncontrolled allergic disease frequently utilize the healthcare system, with approximately one million emergency department visits in the US in 2020 being attributed to asthma exacerbations (1). Additionally, allergic diseases affect patient quality of life, (3) and the healthcare costs associated with allergic disease can be burdensome for families and the healthcare system (3). Families and/or persons living in poverty and patients from minoritized communities are more likely to experience adverse health effects of chronic allergic conditions (4–6) as allergic disease morbidity and decreased quality of life may disproportionately impact disadvantaged populations (4). Moreover, some patients do not respond to standard allergic disease therapies (7). Therefore, additional methods such as allergen reduction through environmental control measures could lead to improvement of symptomology and quality of life. Identifying effective mitigation strategies to reduce allergen exposures could be utilized to decrease allergic disease burden, reduce healthcare costs, and improve quality of life.

At the molecular level, mast cells and basophils bearing immunoglobulin E (IgE) receptors have a threshold at which degranulation and mediator release are triggered (8,9). Individuals who are polysensitized may have more severe symptoms compared with patients with monosensitization (10). However, high levels of exposure to a single allergen may be sufficient to trigger mast cell degranulation. It is possible to decrease allergen exposure through avoidance and allergen reduction methods (9). Reduced allergen exposure may decrease an individual’s total allergen exposure below the threshold necessary for triggering allergic symptoms (9).

Indoor allergen exposure has been extensively linked to allergic rhinitis and asthma morbidity (11–18). Common indoor allergens include dust mites (DM), cats, dogs, rodents, and cockroaches (11), with indoor allergen exposure being a known risk factor for allergic sensitization (17). One strategy to reduce allergic disease burden is through allergen exposure reduction, which can depend on the size of the allergen particles (19). DM and cockroach are most commonly found in settled dust as they are found on large particles and therefore measures for successful allergen reduction are aimed at settled dust (19,20). This is in contrast to cat, dog, and mouse allergens which are most commonly associated with small particles and are, therefore, readily airborne (19,20). Here allergen exposure reduction is aimed at reducing both allergen reservoirs in settled dust and those in the air (19,20).

Strategies for reducing the presence of indoor allergens in homes have been investigated for individual allergens as well as multi-allergen approaches (Table 1). In this review, we will assess the available evidence on the effect of environmental control measures in reducing indoor allergen exposure and the potential clinical impact of these measures. We provide an up-to-date overview of single and multifaceted environmental control interventions from the last decade for the most common indoor allergens. Furthermore, we evaluate the outcomes of these interventions in both asthma and allergic rhinitis. We performed an extensive literature search on PubMed using the key words: allergen avoidance, aeroallergen reduction, indoor allergens, asthma, allergic rhinitis, dust mite allergen reduction, cat allergen, dog allergen, cockroach allergen, mice allergen, mold allergen. We focused primarily on articles published in the last 5 years.

Table 1:

Studies that have elucidated indoor allergen removal

Study	Allergen	Methodology	Summary of results
Rabito et al.	Cockroach	Enrolment included 102 children-adolescents from 5–17 years of age with moderate to severe asthma in a 12-month randomized controlled trial. This study tested the use of insecticidal bait on cockroach counts and asthma morbidity.	Asthma morbidity was improved with this single intervention.
Chen et al.	House Dust Mite	Sixty-six dust mite sensitive children 3–12 years of age with asthma and allergic rhinitis were assigned an acaricidal bait intervention or placebo intervention.	Dust mite exposure was reduced and rhinitis symptoms improved in the Acaricidal bait group when compared to the placebo group.
Terreehorst et al.	House Dust Mite	279 allergic rhinitis patients were randomly assigned to receive impermeable or non-impermeable mattress/pillow/blanket covers.	Covers with mite-proof bedding reduced the level of exposure to mite allergens.
Murray et al.	House Dust Mite	434 mite-sensitized children (ages 3–17) with asthma were randomized to receive mite-impermeable or control bed encasings.	Mite-impermeable encasings reduced asthma exacerbations.
Maya-Manzano et al.	House Dust Mite, Cat, and Dog	Sampled indoor air (with and without air filtration) with a cascade impactor in homes.	Dust mite, cat and dog allergens were effectively removed with air filtration.
Green et al.	Dog	The effect of a HEPA air cleaner was investigated in nine homes with a dog.	HEPA air cleaners effectively reduced airborne Can f 1 in homes with dogs.
Francis et al.	Cat and Dog	A randomized, parallel-group study evaluating the air cleaners in living/bedrooms of thirty asthmatic cat and dog sensitized adults sharing a home with cats or dogs.	Asthma outcomes were improved with the placement of air cleaners.
Matsui et al.	Mouse	Randomized clinical trial of mouse-sensitized and exposed children and adolescents (aged 5–17 years) to receive professionally delivered integrated pest management intervention (IPM) plus pest management education versus pest management education alone	There was no significant difference in maximal symptom days at 12 months between the two groups.
Phipatanakul W	Mouse	Eighteen homes of sensitized children and mild persistent asthma were randomized into intervention homes (received an integrated pest management intervention) and control homes (no intervention). Dust was analyzed for major allergens following the interventions and compared with control homes	Mouse allergen levels were significantly reduced during a 5-month period using IPMs.
Phipatanakul W	Pest	Randomized clinical trial of 236 students with asthma who were randomized to IPM by school and HEPA filter purifiers by classroom	The use of a school-wide IPM program or classroom HEPA filter purifiers did not significantly reduce asthma symptom-days.
Morgan WJ	Cockroach and Dust mite	Randomized controlled trial of 937 children with atopic asthma (5 to 11 years) evaluating education and remediation for exposure to both allergens and environmental tobacco smoke.	An individualized, home-based, comprehensive environmental intervention decreased exposure to cockroach and dust-mite allergens and reduced asthma-associated morbidity.

HOUSE DUST MITE:

House dust mite exposure in mite-sensitized individuals has been linked to increased asthma severity and perennial allergic rhinitis (21–23). Numerous studies have tried to determine if reduced DM exposure leads to clinical benefit in patients with AR and asthma (24,25) and several mechanisms for dust mite exposure reduction/avoidance have been elucidated (24–35). The most successful interventions include mattress/pillow covers, humidity/temperature control, and mite removal through vacuuming (26–35).

Mattresses/Pillow covers:

A multicenter randomized, double-blind, placebo-controlled trial evaluating a year of use of impermeable bedding covers in the bedrooms of 232 pediatric and adult patients with rhinitis who were sensitized to house dust mites demonstrated that mite-proof bedding covers reduced allergen levels, but did not lead to clinical improvement (26). Another study evaluated the use of dust mite-impermeable covers in mite-sensitized children, and the risk of developing severe asthma exacerbations (27). This randomized, double-blind, placebo-controlled, parallel-group study demonstrated that mite-impermeable encasings were effective in lowering hospitalizations (due to asthma exacerbations), but not the number of oral steroid courses (27). A more recent study revealed that the use of impermeable covers on mattresses reduced levels of dust mite by greater than 70% and subsequently reduced risk of ED visits and asthma related exacerbations (24). This simple measure may therefore reduce the health care burden of asthma exacerbations in children with dust mite allergies.

Humidity control:

Dust mites thrive in humid environments so humidity control, through dehumidification, is a key factor in managing dust mite populations (28,29,30). This is largely unnecessary in dry, arid regions and less effective in consistently humid tropical climates where dust mites are likely to flourish regardless of humidity control measures (30).

Vacuum cleaners:

Daily vacuum cleaning of mattresses, furniture, and carpets over time reduces house dust mite allergen levels (34). A single-blind, randomized parallel trial in South Korea including forty children between the ages of 6 and 12 years with mild persistent AR and sensitization to only HDM showed that daily vacuuming reduced dust weight and symptoms of allergic rhinitis (35). However, in this study, the concentration of DM allergen did not significantly decrease (35).

Removal of or covering of carpets and furniture coverings:

Carpet and furniture with woven upholstered fabrics are important reservoirs of dust mite allergen (36). Some studies suggest that removing carpets or furniture coverings can reduce exposure to dust mites and allergens (37,38), but the overall evidence for effective allergen reduction and clinical benefit is limited. These strategies require comprehensive cleaning procedures, higher financial costs, and are not feasible for families who do not own their homes or are limited from begin able to remove the carpet. Therefore, these practices are not generally recommended as primary approaches for allergen reduction.

Household Pets (CAT, DOG):

The prevalence of allergic sensitization to furry animals has been rising (39–43) and pet allergen exposure is among the leading causes of allergic asthma symptoms (39).

One study evaluated US homes to better characterize exposures to Can f 1 (dog allergen) and Fel d 1 (cat allergen) (40). Data was obtained from 831 US homes using the National Survey of Lead and Allergens in Housing survey. Concentrations of Can f 1 and Fel d 1 were obtained from vacuumed-collected dust samples from the bedroom and living room furniture and floors (40). A dog or cat lived in only 49.1% of homes, however, Can f 1 and Fel d 1 were detected in 100% and 99.9% of homes, respectively (40). This study demonstrates that even the majority of homes without pets have detectable levels of Can f 1 and Fel d 1, highlighting the transportability of these allergens.

Pet ownership providers health benefits, including positive influences on mental health (41,44). It is often undesired and an unrealistic option to remove pets from the home to reduce allergen exposures (44). Furthermore, many patients have difficulty complying with avoidance recommendations (44). Therefore, it is important to discover effective avoidance measures along with mechanisms for removal of allergens to ensure patients and families have the best options to navigate pet allergies.

CAT:

Cats are the most common contributor to mammalian-based allergies (39). Fel d 1 is the most common cat allergen (39). Fel d 1 is ubiquitous, measured in high quantities (exceed threshold value associated with sensitization) in indoor settings such as homes (even without cats), classrooms, various work settings, vehicles, and public transportation (40–42). Therefore, successfully reducing cat allergen exposure in homes may not lead to clinical improvement without limiting exposures to potentially high levels of cat allergens at work, in homes of cat-owning relatives or friends, or in public places (39–44).

Cat-sensitized children with asthma experience twice as many asthma symptom days (45). Furthermore, cat-sensitized children, who reported the absence of cat exposures, require more frequent dosing of β-agonists and steroids when sharing classrooms with classmates with cat ownership (45). Standard oral and nasal allergy treatments have pharmacological and socioeconomic limitations and allergen immunotherapy (AIT) is time intensive and may not always be effective (46). Therefore, innovative approaches to better manage cat allergy are needed.

Most commonly, cat removal from the household is recommended as the most clinically effective measure (47). Fel d 1 is a “persistent” allergen, and it may take months for the allergen load to be reduced once a cat is removed from the household. One study observed that it may take up to 20 weeks following removal of the cat for Fel d 1 levels to lower to levels in homes without cats (48). It may take even longer for symptoms to improve following removal of the cat from the household, particularly if the household is carpeted (47,48).

Several studies have demonstrated that air cleaners can reduce airborne Fel d 1 in asthmatic patients allergic and exposed to cats, but clinical outcomes vary in these studies. A double-blind, placebo-controlled, cross-over study in young asthmatic patients sensitized and exposed to pets in the home revealed application of air cleaners in homes (bedrooms and living rooms) led to a significant reduction in peak flow amplitude and improvement in airway hyperresponsiveness (49). Conversely, a randomized controlled trial of 36 asthmatic children sensitized to cat with significant exposure to cat allergen (Fel d 1>500 ng/g of carpet dust) evaluated the effect of high-efficiency particulate arresting (HEPA) air cleaners in the home (bedroom and living room) (50). Although airborne cat allergens were retained and effectively lowered from ambient air with the use of HEPA air cleaners, disease activity was not affected and there was negligible change in allergen concentrations in bulk dust samples in this study (50). A double-blind, placebo-controlled trial of 35 cat-allergic patients living with one or more cats evaluated the effect of a HEPA cleaner on cat-induced asthma and rhinitis (51). No differences were detected in settled-dust allergen levels, nasal/chest-symptom scores, sleep disturbance, morning or afternoon peak-flow rates, or rescue medication use (51). Overall, the combination of a HEPA room air cleaner, mattress and pillow covers, and cat exclusion from the bedroom did reduce airborne cat-allergen levels (51). However, there was no effect on disease activity (51). A more recent randomized, cross-over, double-blind placebo-controlled study demonstrated that air cleaners prevented early and late asthmatic responses in asthmatics cat allergenic patients during cat allergen exposure (52).

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standardized efficiency testing methods by measuring and counting particles across the filters (53). Updated ASHRAE guidelines recommend air filters (with a MERV (Minimum Efficiency Reporting Value) rating of 10 or higher are best for removing pet dander) (53,54). One study conducted a modeling analysis assessing the effectiveness of filter-based interventions to reduce airborne triggers for allergies and asthma (55). This analysis concluded that use of air filters with MERV12 or higher, effectively reduced indoor levels of cat allergens (55). An air filtration removal efficiency of >70% for Fel d 1 can reduce allergen concentrations by >50% (55). Very high removal efficiency filters (a 16 on the nationally recognized Minimum Efficiency Removal Value (MERV) rating system), tend to be minimally more effective than MERV12 or 13 rated filters (55).

Thus, there is sufficient evidence that air filtration does reduce indoor cat allergen levels and portable room air cleaners with new generation HEPA filters appear to be beneficial for airborne Fel d 1 air filtration. Clinical benefit of asthmatic patients with cat allergies has been demonstrated.

Additional environmental control measures aimed to decrease the concentration of cat allergens have yielded mixed results (56). Excluding the cat from the bedroom, removal or covering of cloth-upholstered furniture, weekly vacuuming or steam cleaning/wet mopping floors and surfaces, and regular bathing of cats have been shown to effectively lower cat allergen levels (56). However, these measures are effort-intensive, costly, and may be difficult to sustain long term effectiveness (56). Furthermore, these effects may be transient and data is inconclusive in demonstrating clinical improvements in asthma and rhinitis outcomes (56).

In a randomized, parallel-group study of 30 cat-sensitized adults with asthma living in a home with cats revealed clinical improvement in asthma (based on a combined asthma outcome) with the combined use of free-standing HEPA and frequent vacuuming when compared to using vacuum cleaners alone (57). No difference was noted with regards to objective lung function, reservoir pet allergen and airborne pet allergen (57).

Several new strategies to decrease allergen production/exposure in cats have been explored (58–60). There is evidence suggesting that, in cats, dietary alterations may affect allergen production, although clinical efficacy of this modification has not been investigated (60). More recently, the investigation of a specific neutralizing antibody (anti Fel d 1 IgY) in cat’s food, was found to reduce the major cat allergen (Fel d 1), decreasing exposure load and subsequent allergic symptoms (58). However, the effectiveness in cat-allergic patients is still unknown (58).

DOG:

Dogs are another common source of indoor allergens (61). Canis familiaris allergen 1 (Can f 1) and Canis familiaris allergen 2 (Can f 2) are the two major allergens produced by dogs (62).

As with cat ownership, dog avoidance within households can be very difficult and pet removal can be associated with major emotional impacts (44). Standard asthma and allergy treatments have limitations. Therefore, alternative approaches to manage dog allergies may provide clinical benefit.

One small study of 9 participants evaluated the effect of a HEPA filter air cleaner in reducing dog allergen levels (63). The aim of the study was to evaluate the use HEPA filter air cleaner to reduce airborne Can f 1 in homes with a dog (63). Samples were collected from two rooms of each house, one of which contained the dog (63). Airborne Can f 1 levels, at baseline, were roughly 4-fold greater when samples were collected with a dog in the room than when the dog was elsewhere in the house (63). The study concluded that HEPA air cleaners reduce airborne Can f 1 in homes with dogs. The study also revealed that the total allergen load inhaled was lower when dogs were prevented access to the bedroom (63).

Furthermore, a study on 22 households of participants from 18–65 years of age revealed that portable air filtration devices with an adequate clean air delivery rate was effective in reducing exposure to airborne dog allergens and also particulate matter from ambient indoor air (31).

Another study evaluated the effectiveness of washing machines and driers to remove dog and cat hair and their allergens (64). This study evaluated the success of pet allergen removal through the use of a mechanical dryer without mechanical washing (64). Mechanical washing without a detergent lowered both Fel d 1 and Can f 1 (64). Mechanical drying alone was just as effective as mechanical washing for removing Can f 1, but was less effective for reducing Fel d 1 (64). The study concluded that mechanical washing with detergent is a useful mechanism for reducing dog and cat allergens from fabrics (64). Using just a dryer without washing may be an alternative method to remove allergens in cases that mechanical washing may be difficult. The effect of bathing the dog regularly and frequent changing of clothes have not revealed allergen exposure reduction or differences in clinical outcomes (64).

In evaluating different dog breeds, patients with known sensitization will often interrogate about “hypoallergenic” breeds. Studies have demonstrated that Can f 1 have similar airborne presence in homes with supposedly hypoallergenic dog breeds when compared to other breeds. There is currently no evidence to suggest that “hypoallergenic” dog breed offer reduced levels of dog allergens nor do they provide clinical benefit to dog-sensitized individuals (65).

PESTS (mouse and cockroach):

MOUSE:

Mice are ubiquitous and play a major role in allergic respiratory disease (66). Mus m 1, excreted in mouse urine, is the major mouse allergen. Mus m 1 can remain airborne for long periods of time and has been shown to be detectable in settled dust in a high percentage of both urban and suburban homes (66, 67). Mouse exposure in mouse-sensitized children is associated with increased asthma morbidity severity, particularly in low-income, minoritized populations (68). Reduced mouse allergen exposure is associated with improvements in asthma symptoms and increased lung function growth (68,69). Parental reports about the home environment can provide valuable information to guide treatment recommendations for urban children. In one study, parents of 300 children between the ages of 2 and 6 years old in urban Baltimore completed surveys to identify allergen exposures and determine the clinical relevance of exposures (70). This study found that parent report of mouse exposure in the home was predictive of asthma symptoms (70).

One approach to reducing mouse allergen exposure is integrated pest management (IPM), which is a multidisciplinary approach that implements several pest control strategies aimed to reduce allergen levels (71). IPM strategies include rodent trap setting, blocking pest access by fixing compromised housing, careful disposal of waste, and selectively applying low-toxicity pesticides. Additionally, removing reservoirs like carpeting or other areas containing allergen may be helpful in reducing mouse allergen exposure (71). However, IPM may be costly and difficult to implement.

The Mouse Allergen and Asthma Intervention Trial (MAAIT) was a randomized clinical trial of 361 mouse-sensitized and exposed children and adolescents (aged 5–17 years) with asthma that compared IPM and education to pest management education alone (68). There was no significant difference found in maximal symptom days at 12 months between the two groups in this study (68). When the groups were combined for analysis, approximately 45% of participants’ homes had at least a 90% reduction in mouse allergen during the study, which was associated with fewer acute care visits and fewer hospitalizations per person-year (68). This evaluation demonstrated that in low-income children with mouse sensitization and persistent asthma, mouse allergen reduction was associated with clinical improvement (68). However, the concentration of mouse allergen remained in range that would be associated with increased risk of asthma morbidity (68).

A secondary analysis of the MAAIT revealed housing characteristics that were associated with a clinically meaningful reduction of allergens such as higher percentage of a clear floors in the bedroom, and rodent holes in the living room (likely because rodent holes are identifiable and a repairable measure) (72,73). These findings highlight the impact of effective mouse allergen reduction techniques and the critical role that housing disrepair plays in pest allergen exposure.

Another source for mouse allergen exposure may be in urban schools (74). The School Inner-City Asthma Study (SICAS 1), between 2008 and 2013 revealed that mouse allergen was detected in 99% of classrooms (74). This study demonstrated that children had worsening asthma symptoms when exposed to mouse allergen in schools (74). The Second School Inner-City Asthma (SICAS 2) revealed that IPM programs in schools unfortunately did not significantly decrease asthma symptom days (75).

At the population level, further studies on IPM and education on implementing IPM are needed, especially for urban and suburban, low-income communities. At the patient level, additional resources such as housing mobility programs, housing regulation legislation, pest management services, and local resources from health departments or non-profit organizations may provide patients and families the best approach for reducing mouse exposure.

COCKROACH:

The major cockroach allergens include Bla g 1, Bla g2, and Per a 1 which are found in the saliva, stool, and debris of the two most common cockroaches- German and American cockroach; Blatella germanica and Perplaneta americana, respectively (76,77). Like mice, cockroaches are ubiquitous and more prominent in urban settings and low-income households (77–79). Cockroach allergen exposure has been linked to worsened asthma outcomes, measured by utilization of health care as a result of asthma related events (77,80). Historically, one landmark study found that children who were both sensitized to cockroach allergen (Bla g 1) and exposed to high levels of this allergen had more hospitalizations a year, compared with other children. They also had significantly more days of wheezing, missed school days, and nights with lost sleep (77).

As with mice, cockroach allergen exposure can be reduced using IPM, including the use of pesticides, timey waste disposal, and home repairs (81–84). In children with asthma living in low-income households, the use of IPM use is associated with reduction of cockroach allergens when compared to homes without interventions. (82–85).

One randomized control trial evaluating 937 children aged 5-to-11 years with atopic asthma revealed that the implementation of a personalized environmental intervention measures in single households not only led to lower cockroach allergen levels, but a reduction of asthma associated morbidity (83). A different randomized control trial focusing on nonsmoking adults and children with mild-to-severe persistent asthma revealed no difference in the asthma controller medication use between groups with cockroach exposure reduction. However, in this study, cockroach allergen in settled dust remained comparable in both the control and intervention groups, likely explaining the lack of clinical effect (84).

One of the most effective strategy to reduce cockroach allergen levels may be the use of gel bait insecticides (85–87) One recent randomized control trial (New Orleans Roach Elimination Study) focused on 102 children aged 5-to-17 years with moderate-to-severe asthma evaluated the utilization of insecticidal bait on cockroach counts and asthma morbidity. The use of insecticidal bait was associated with fewer asthma symptom days, decreased hospitalizations, and improved lung function (85). While effective, these allergen reduction measures can be cost prohibitive. More resources are needed to provide those in low-income households with access to education and interventions aimed at cockroach reduction.

INDOOR MOLD:

Indoor molds have been associated with uncontrolled allergic rhinitis and asthma exacerbations and mold sensitization may serve as a risk factor for development of asthma (88,89,90). Some molds can accumulate indoors, tend to proliferate on surfaces, and have a tendency to grow in moist environments (88). One study in children grades one through six demonstrated that increased mold levels in indoor play areas and mattresses (found in vacuumed dust samples) were associated with asthma (89). Several strategies have been studied with variable effectiveness in reducing mold exposure including removal of mold from mold-laden surfaces, installation of ventilation systems, preventing water extravasation and intrusion, applying fungicides, and dehumidification (91). These mitigation strategies are often challenging, expensive, and time consuming for families. A Cochrane systematic review of 12 studies with greater than 8000 patients found moderate to very low-quality evidence that asthma related symptoms decreased with repairing mold-damaged houses (92). Overall, there is limited evidence for consistent and significant clinical benefits particularly due to methodological challenges in accurately measuring mold exposure and isolating its effects on patients with asthma and allergic rhinitis.

RECOMMENDATIONS FROM GUIDELINES:

According to the updated 2024 Global Strategy for Asthma Management and Prevention from the Global Initiative for Asthma, allergen avoidance is not generally recommended as a strategy in asthma control due to the limited evidence that avoidance of indoor allergens provides clinical benefit for sensitized asthma patients (93). The 2024 update reports that single allergen avoidance strategies demonstrate little evidence for clinical benefit while multi-component avoidance strategies have limited evidence for clinical benefit and that the avoidance of allergens can be complicated, burdensome, and expensive (93). Furthermore, the absence of validated methods for determining which patients may have clinical benefit does not lead to consensus support for allergen avoidance in asthma patients (93). Conversely, The National Asthma Education and Prevention Program (NAEPP) expert panel conditionally recommends a multicomponent allergen-specific mitigation intervention in asthma patients with symptoms related to specific indoor allergen exposures (confirmed by history taking or allergy testing) (94). For asthma patients with sensitization to dust mites, the panel recommends “impermeable pillow/mattress covers only as part of a multicomponent allergen mitigation intervention, not as a single-component intervention (94).” For asthma patients with sensitization to pests (cockroaches and rodents), the panel “recommends the use of integrated pest management alone, or as part of a multicomponent allergen-specific mitigation intervention (94).”

CONCLUSION:

Allergen exposure intervention studies have yielded mixed results with regard to specific environmental control measures in reducing indoor allergen levels and in improving clinical outcomes of allergic disease. This becomes even more challenging in polysensitized individual where substantial multifaceted reduction approaches may be needed to reduce the total “allergen load” and to have a clinical impact. Furthermore, many indoor allergens are ubiquitous, found in public locations, and difficult to remove from the home, making long-lasting reduction strategies difficult to achieve.

To date, the most successful intervention for reducing house dust mite exposure is multifaceted avoidance and reduction strategies through the implementation of mattress/pillow encasings, humidity/temperature control, and frequent vacuuming (at least weekly) which may effectively reduce mite allergen levels. However, these measures have not led to improved clinical outcomes in many studies.

With regard to cat and dog allergens, HEPA filters have been shown to be successful in reducing furry animal allergen exposure. For cat allergen exposure, the combined use of free standing HEPA filters and frequent vacuuming showed improvement in asthma control compared to using vacuum cleaners alone. To date, the most effective control factor, with regard to furry pets, is pet removal. However, pet removal can have a major social and emotional impact and is often recommended only in severe circumstances. The removal or covering of upholstered furniture, weekly vacuuming or steam cleaning/wet mopping floors and surfaces, and regular bathing of cats/dogs have been shown to effectively lower the levels of allergens but these measures are effort intensive, costly, and may be difficult to sustain long term effectiveness particularly given the ubiquitous and long-lasting nature of these allergens.

Pest allergen reduction presents a challenge due to the widespread distribution and abundance, particularly in low-income, urban communities. Integrated pest management (IPM), which are multidisciplinary approaches that implements several pest control strategies aimed to reduce allergen levels, has been shown to be successful and specific strategies such as housing repairs, careful and timely waste disposal, and applying low-toxicity pesticides have been successful in reducing pest allergens and achieving clinical improvements. One of the most effective methods for removing is the use of insecticides bait which can be purchased online, or used by pest management services.

While decades of studies have been devoted to environmental interventions, a clear answer has not emerged. Further large and well-designed trial studies will be needed to elucidate the effectiveness of single versus multicomponent environmental control interventions.

In summary, the management of patients with allergic rhinitis and/or asthma requires careful attention to potential environmental triggers (Table 2). This begins with a careful environmental history followed by allergy testing to determine the individual patient’s allergic sensitizations, as well as the degree of sensitization. With this information patients should be provided individualized recommendations based on the best science presented here.

Table 2:

Recommended interventions for reducing indoor allergens.

Allergen	Recommended Interventions
House Dust Mite	Frequent vacuuming (at least weekly) Allergen-proof mattress/pillow covers Temperature control (humidity)
Cat	HEPA filter with maximized avoidance with the animal* Removal or covering of cloth-upholstered furniture Weekly vacuuming Steam cleaning/wet mopping floors Regular bathing of animals Pet removal from home (in severe circumstances)
Dog	HEPA filter with maximized avoidance with the animal* Pet removal from home (in severe circumstances) * Removal or covering of cloth-upholstered furniture Weekly vacuuming Steam cleaning/wet mopping floors Regular bathing of animals
Mouse/Cockroach	IPM strategies such as Low-toxicity pesticides Timely waste disposal Home repairs Additional support: Housing mobility programs Housing regulation committees Pest management services Local resources from health departments or non-profit organizations

^*Denotes first line intervention