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Improving indoor environments: Reducing allergen exposures

      Homes cannot be made allergen free, but exposure to the major indoor allergens can be reduced. All reduction recommendations are based on the principle of reducing or isolating the source, and certain recommendations can be made on the basis of published evidence. House dust mite avoidance measures include fitting allergen-proof mattress and pillow encasings, washing bedding regularly, and reducing humidity. Furred pet avoidance requires removal of the pet form the home, followed by thorough and repeated cleaning; room air cleaners, washing the pet, and isolating the pet from a bedroom are ineffective alternatives. Cockroach allergen avoidance begins with effective pest control, followed by thorough and repeated cleaning; 1 to 2 months are required to eliminate roaches, and an additional 4 to 6 months are required to remove residual allergen. Once allergen levels have been reduced, continued efforts are necessary to maintain the home free of allergen sources.

      Key words

      Abbreviation used:

      HEPA (High-efficiency particulate air)
      Although it is impossible to make indoor environments allergen free, we have learned a great deal in the last several decades about effective methods to decrease excessive indoor allergen exposure. We have adapted the principles of exposure assessment and exposure reduction from those developed in occupational settings
      • Corn M.
      Assessment and control of environmental exposure.
      to home environments. As shown in schematic form in Fig 1, one of these principles is that an exposure dose is dependent both on the concentration inhaled into the respiratory tract and the duration of the exposure. The best estimates of exposure dose have proved to be allergen concentration in bedding, although recent technology
      • De Lucca S.D.
      • Taylor D.J.M.
      • O'Meara T.J.
      • Jones A.S.S.
      • Tovey E.R.
      Measurement and characterization of cockroach allergens detected during normal domestic activity.
      might allow us to better estimate the inhaled dose. Another principal is that the most effective method of reducing exposure dose is to remove the source of the contaminant. In practice, some sources (house dust mites and cockroaches) have been easier to remove than others (pets). When the source cannot be removed, pollutant removal should start as close to the source as possible.
      Figure thumbnail gr1
      Fig 1Schematic of allergen emission, transmission, and airway exposure on the basis of the model developed for occupational pollutant exposure. Adapted with permission from Corn.
      • Corn M.
      Assessment and control of environmental exposure.
      A number of excellent and complete reviews have summarized the details of allergen reduction
      • Tovey E.
      • Marks G.
      Methods and effectiveness of environmental control.
      • Institute of Medicine Committee on the Assessment of Asthma and Indoor Air
      Clearing the air: asthma and indoor air exposures.
      • Bush R.K.
      • Eggleston P.A.
      Guidelines for control of indoor allergen exposure.
      and their health effects on sensitized individuals, and therefore this review will concentrate on recent advances in reducing exposures, without summarizing the health effects.

      House dust mite

      House dust mite allergens are carried on relatively large particles (10-30 μm) that do not remain airborne for long. The mites infest fabrics (especially bedding), are not particularly mobile, and have fastidious growth requirements, making the source elimination relatively easy. At the top of the list of effective methods to reduce house dust mite is allergen-proof encasings fitted to the mattress and pillow.
      • Tovey E.
      • Marks G.
      Methods and effectiveness of environmental control.
      • Institute of Medicine Committee on the Assessment of Asthma and Indoor Air
      Clearing the air: asthma and indoor air exposures.
      • Bush R.K.
      • Eggleston P.A.
      Guidelines for control of indoor allergen exposure.
      These covers are available by mail or in retail stores and are breathable, comfortable, and nearly 100% exclusive.
      • Vaughan J.W.
      • McLaughlin T.E.
      • Perzanowski M.S.
      • Platts-Mills T.A.E.
      Evaluation of materials used for bedding encasement: effect of pore size in blocking cat and dust mite allergen.
      More than a dozen clinical trials of allergen-proof encasings have been published that were at least 3 months long and reported mite allergen levels in bedding.
      • Cloosterman S.G.M.
      • Schermer T.R.J.
      • Bul-Hofland I.D.B.
      • Vanderheid S.
      • Brunekreef B.
      • van den Elshout F.J.J.
      • et al.
      Effects of house dust mite avoidance measures on Der p 1 concentrations and clinical condition of mite-allergic asthmatic patients using no inhaled steroids.
      • Custovic A.
      • Simpson B.M.
      • Simpson A.
      • Hallam C.
      • Craven M.
      • Brutsche M.
      • et al.
      Manchester Asthma and Allergy Study: low allergen environment can be achieved and maintained during pregnancy and in early life.
      • Ehnert B.
      • Lau-Schadendorf S.
      • Weber A.
      • Beuttner P.
      • Schou C.
      • Wahn U.
      Reducing domestic exposure to dust mite allergen reduces bronchial hyperreactivity in sensitive children with asthma.
      • Frederick J.M.
      • Warner J.O.
      • Jessop W.J.
      • Enander I.
      • Warner J.A.
      Effect of a bed covering system in children with asthma and house dust mite hypersensitivity.
      • Halken S.
      • Host A.
      • Niklassen U.
      • Hansen L.G.
      • Nielsen F.
      • Pedersen S.
      • et al.
      Effect of mattress and pillow encasings on children with asthma and hose dust mite allergy.
      • Luczynska C.
      • Tredwell E.
      • Smeeton N.
      • Burney P.
      A randomized controlled trial of mite allergen-impermeable bedcovers in adult sensitized asthmatics.
      • Marks G.B.
      • Tovey E.R.
      • Green W.
      • Shearer M.
      • Salome C.M.
      • Woolcock A.J.
      House dust mite allergen avoidance: a randomized controlled trial of surface chemical treatment and encasement of bedding.
      • Nishioka K.
      • Yasueda H.
      • Saito H.
      Preventive effect or bedding encasements with microfine fibers on mite sensitization.
      • Owen S.
      • Morganstern M.
      • Hepworth J.
      • Woodcock A.
      Control of house dust mite antigen in bedding.
      • Paul K.
      • Klettke U.
      • Wahn U.
      the combined influence of immunotherapy and mite allergen reduction on bronchial hyperresponsiveness in mite-sensitive asthmatic children.
      • Rijseenbeck-Nouwens L.H.M.
      • Oosting A.J.
      • deBruin-Weller M.S.
      • Bergman I.
      • de Monchy J.G.R.
      • Postma D.S.
      Clinical evaluation of the effect of anti-allergic mattress covers in patients with moderate to severe asthma and house dust mite allergy: a randomized double blind placebo controlled study.
      • Sporik R.
      • Hill D.J.
      • Thompson P.J.
      • Stewart G.A.
      • Carlin J.B.
      • Nolan T.M.
      • et al.
      The Melbourne house dust mite study: long-term efficacy of house dust mite reduction strategies.

      van der Heide S, Kauffman HF, Dubois AEJ, de Monchy JGR. Allergen-avoidance measures in homes of house-dust-mite-allergic asthmatic patients: effects of acaricides and mattress encasing. Allergy 197;52:921-7.

      • Vojta P.J.
      • Randels S.P.
      • Stout J.
      • Muilenberg M.
      • Burge H.A.
      • Lynn H.
      • et al.
      Effects of physical intervention on house dust mite allergen levels in carpet, bed and upholstery dust in low-income, urban homes.
      • Woodcock A.
      • Forster L.
      • Matthews E.
      • Martin J.
      • Letley L.
      • Vickers M.
      • et al.
      Control of exposure to mite allergen and allergen impermeable bed covers for adults with asthma.
      All of these trials report reduced allergen concentrations, but the degree of allergen reduction varied widely, from 39% to 99.9% (median, 89%), as did the final allergen concentrations achieved (range, 0.01-8.50 μg/g; median, 0.77 μg/g). It is not clear why such a wide range of effectiveness was seen in these trials, but the variations were not easily explained by the level of mite contamination, and many of the trials included bedding laundry, tannic acid, or acaricides. In addition, bedding allergen levels have been shown to continue to decrease with observations up to a year, suggesting that repopulation of bedding cover fabric is not common.
      Other first-line measures include thorough vacuum cleaning and washing all bedding (sheets, blankets, comforters, and bedspreads). Vacuuming reduces the bulk of household dust and reduces the overall exposure burden but does not change the concentration of allergen (ie, micrograms per gram of settled dust).
      • Munir A.K.
      • Einarsson R.
      • Dreborg S.K.
      Vacuum cleaning decreases the levels of mite allergens in house dust.
      Washing sheets, pillowcases, blankets, and mattress pads at least weekly in warm water with detergent and with 8- to 10-minute cycles removes virtually all mite and animal allergen.
      • McDonald L.G.
      • Tovey E.
      The role of water temperature and laundry procedures in reducing house dust mite populations and allergen content of bedding.
      Dry cleaning
      • Vandehove T.
      • Soler M.
      • Birnbaum J.
      • Charpin D.
      • Vervloet D.
      Effect of dry cleaning on the mite allergen levels in blankets.
      and prolonged tumble drying
      • Miller J.D.
      • Miller A.
      Ten minutes in a clothes dryer kills all mites in blankets.
      effectively kill mites but are less effective at removing allergens.
      Second-line measures include relocating the bedroom, application of acaricides (eg, benzyl benzoate), dehumidification, and removal of wall-to-wall carpeting. Relocating the patient's bedroom out of the basement has been recommended, but the only reported study of basement carpets found that mite allergen concentrations were almost identical to those of carpets elsewhere in the home.
      • Woodfolk J.A.
      • Hayden M.
      • Miller J.
      • Rose G.
      • Chapman M.
      • Platts-Mills T.A.E.
      Chemical treatment of carpets to reduce allergen: a detailed study of the effects of tannic acid on indoor allergens.
      Removing fabrics, such as curtains and furniture, seems logical because they might support mite growth, but this has not been shown to increase the effect of vacuuming and bedding covers alone. Removing wall-to-wall carpeting is difficult but justifiable because house dust mite levels are higher in wall-to-wall carpet compared with those seen in uncarpeted areas, and bedroom floor levels are reduced when carpeting is removed.
      • Sporik R.
      • Hill D.J.
      • Thompson P.J.
      • Stewart G.A.
      • Carlin J.B.
      • Nolan T.M.
      • et al.
      The Melbourne house dust mite study: long-term efficacy of house dust mite reduction strategies.
      Acaricides are effective in the laboratory, but field trials have generally found that carpet dust mite allergen is reduced minimally, probably because it is so difficult to get the material into the deepest areas of the carpet.
      • Hayden M.L.
      • Rose G.
      • Diduch K.B.
      • Chapman M.D.
      • Heymann P.W.
      • Platts-Mills T.A.E.
      Benzylbenzoate moist powder: investigation of acaricidal activity in cultures and reduction of dust mite allergens in carpets.
      The evidence supporting measures to reduce indoor humidity is inconsistent. Trials in England showed that portable dehumidifiers
      • Custovic A.
      • Taggart S.C.O.
      • Kennaugh J.H.
      • Woodcock A.
      Portable dehumidifiers in the control of house dust mites and mite allergens.
      were not able to reduce median humidity significantly, and mite allergen levels did not change. Central heat exchangers
      • Niven R.M.
      • Fletcher A.M.
      • Pickering A.C.
      • Custovic A.
      • Sivour J.M.
      • Preece A.R.
      Attempting to control mite allergens with mechanical ventilation and dehumidification in British homes.
      were able to maintain indoor relative humidity at less than 40% for the 4 months that they were used, but mite allergen levels in carpets and bedding did not decrease. Arlian et al
      • Arlian L.G.
      • Neal J.S.
      • Morgan M.S.
      • Vyszenski-Moher D.L.
      • Rapp C.M.
      • Alexander A.K.
      Lowering humidity in homes is a practical way to control house dust mites and their allergens in homes in temperate climates.
      installed large portable dehumidifiers in Midwestern US homes and showed that approximately half of the homes were able to maintain relative humidity at less than 51% throughout a 2-year period. Mite allergen in bedding was not measured, but mites and mite allergen in the carpets from these homes decreased 78%. Surprisingly, air conditioning alone was not able to reduce indoor humidity enough to affect mite growth significantly.

      Pet allergen avoidance

      Animal allergens are carried on small particles that remain airborne and are remarkably adherent to surfaces and clothing.
      • Custovic A.
      • Green R.
      • Fletcher A.
      • Smith A.
      • Pickering C.A.C.
      • Chapman M.D.
      • et al.
      Aerodynamic properties of the major dog allergen, Can f 1: distribution in homes, concentration, and particle size of allergen in air.
      Because the source is so mobile in a home, inclined to heavily contaminate a favorite chair or bed, and because families are reluctant to get rid of the pet, source elimination is almost impossible. An atopic patient who is sensitized to cat or dog allergen should not live with a pet in their home. Air filters should be helpful in reducing exposure to airborne pet allergen particles. Their stickiness leads to widespread distribution, so that animal allergen can be found in public buildings, such as schools,
      • Almqvist C.
      • Larrson P.H.
      • Egmar A.-C.
      • Hedren M.
      • Malmberg P.
      • Wickman M.
      School as a risk environment for children allergic to cats and a site for transfer of cat allergen to homes.
      • Custovic A.
      • Fletcher A.
      • Pickering C.A.C.
      • Francis H.C.
      • Green R.
      • Smith A.
      • et al.
      Domestic allergens in public places III: house dust mite, cat, dog and cockroach allergens in British hospitals.
      and in homes without a pet, although concentrations are 10 to 1000 times higher in homes with a pet.
      • Wood R.A.
      • Eggleston P.A.
      • Ingemann L.
      • Schwartz B.
      • Graveson S.
      • Terry D.
      • et al.
      Antigenic analysis of household dust samples.
      Once a pet has been removed from the home, allergen levels in settled dust decrease to those seen in homes without cats over 4 to 6 months.
      • Wood R.A.
      • Chapman M.D.
      • Adkinson Jr., N.F.
      • Eggleston P.A.
      The effect of cat removal on Fel d I content in household dust samples.
      Levels decrease much more quickly if extensive environmental control measures are undertaken, such as removal of carpets, upholstered furniture, and other reservoirs from the home. Cat allergen might persist in mattresses for years after a cat has been removed from a home,
      • Van der Brempt X.
      • Charpin D.
      • Haddi E.
      • da Mata P.
      • Vervloet D.
      Cat removal and Fel d 1 levels in mattresses.
      and therefore the purchase of new bedding or impermeable encasements should also be recommended.
      Because so many patients are unwilling to remove their pet, even if they themselves are sensitized, many compromise measures have been suggested. De Blay et al
      • De Blay F.
      • Chapman M.D.
      • Platts-Mills T.A.E.
      Airborne cat allergen (Fel d 1): Environmental control with the cat in situ.
      demonstrated significant reductions in airborne Fel d 1 with a combination of air filtration and washing the cat, but later studies showed that the decrease lasted only a few days.
      • Avner D.B.
      • Perzanowski M.S.
      • Platts-Mills T.A.E.
      • Woodfolk J.A.
      Evaluation of different techniques for washing cats: Quantitation of allergen removed from the cat and effect on airborne Fel d 1.
      The use of room high-efficiency particulate air (HEPA) filters might reduce airborne levels somewhat. When these units are placed in living rooms, airborne levels of cat and dog allergen have been shown to decrease by almost 90%
      • Green R.
      • Simpson A.
      • Custovic A.
      • Faragher B.
      • Chapman M.
      • Woodcock A.
      The effect of air filtration on airborne dog allergen.
      • Gore R.B.
      • Bishop S.
      • Durrell L.
      • Curbishley L.
      • Woodcock A.
      • Custovic A.
      Air filtration units in homes with cats: can they reduce personal exposure to cat allergen?.
      over a period of hours, but similar reductions were seen in control experiments when the units were not running, so that there was no net effect attributable to HEPA air filtration. A later report extended treatment for a year,
      • Francis H.
      • Fletcher G.
      • Anthony C.
      • Pickering C.
      • Oldham L.
      • Hadley E.
      • et al.
      Effects of air filters in homes of asthmatic adults sensitized and exposed to pet allergens.
      demonstrating persistent 90% reductions in allergen levels in both the treatment and control groups. Asthma improved to a statistically greater extent in the treatment group. Both groups also used a HEPA-filtered vacuum cleaner, but settled dust animal allergen levels did not decrease. Another report described a safe room from which the cat was excluded, and vigorous environmental control measures, such as vacuuming, mattress and pillow covers, carpet removal, and room air filters, were tested.
      • Wood R.A.
      • Flanagan E.
      • Van Natta M.
      • Chen P.H.
      • Eggleston P.A.
      A placebo-controlled trial of a HEPA air cleaner in the treatment of cat allergy.
      In this case airborne levels decreased 43% over 3 months, and settled dust allergen levels did not change.

      Rodent allergen avoidance

      Mouse allergen is carried on particles that are small and remain airborne
      • Matsui E.C.
      • Simons E.
      • Rand C.
      • Butz A.
      • Buckley T.J.
      • Breysse P.
      • et al.
      Airborne mouse allergen in the homes of inner-city children with asthma.
      ; like other animal allergens, they are widely distributed and commonly found in homes that are not infested with mice.
      • Cohn R.D.
      • Arbes Jr., S.T.
      • Yin M.
      • Jamarillo R.
      • Zeldin
      National prevalence and exposure risk for mouse allergen in US households.
      On the other hand, families are much more willing to help eliminate the source, making exposure control that much easier. Although the pesticides might be applied in almost any form, the method preferred by pest control companies in inhabited buildings is termed integrated pest management; this includes targeted application of pesticides, together with plugging access cracks and crevices and protection of food sources to reduce the risk of reinfestation. Like other animal allergens, elimination of the source must be followed by vigorous and sustained cleaning to remove allergen. A controlled clinical trial of this approach was reported that included dusting a tracking powder with inandione, a low-toxicity pesticide, in wall voids and pipe chases, as well as placing snap traps.
      • Phipatanukul W.
      • Cronic B.
      • Wood R.A.
      • Eggleston P.A.
      • Shih M.
      • Song L.
      • et al.
      Environmental intervention reduces mouse allergen levels in homes of Boston inner city children with asthma.
      Access holes were filled with copper mesh and caulk sealant, and the family was educated to vacuum aggressively with HEPA-filtered vacuum cleaners, to clean surfaces carefully with mild detergents, and to continue pest control measures. Mus m 1 concentrations in combined dust samples from the floor and bed decreased by 42% (from 5.2 to 2.2 ng/g), whereas levels from control homes actually rose.

      Cockroach allergen avoidance

      Cockroach allergen particles have properties similar to those of mite allergens; 74% to 80% of aeroallergens are associated with particles larger than 10 μm that are detectable mainly after vigorous activity and settle rapidly.
      • Eggleston P.A.
      • Arruda L.K.
      Ecology and elimination of cockroaches and allergens in the home.
      Because the cockroach is highly mobile, allergen is spread widely through a home in bedding, as well as in kitchens; allergen is concentrated in hiding places behind appliances and in cracks and crevices, creating a unique reservoir that is difficult to access.
      Cockroach allergen removal begins with insecticide treatment to reduce the allergen source.
      • Eggleston P.A.
      • Wood R.A.
      • Rand C.
      • Nixon W.J.
      • Chen P.H.
      • Luuk P.
      Removal of cockroach allergen from inner city homes.
      Pesticides incorporated in gels or baits are placed selectively in areas with high insect concentrations and traffic. In addition, bait traps with pesticides, such as abamectin and hydramethylnon, are available to consumers that are just as effective as the gel baits if used properly. Typically, successful treatments provide significant reduction within 2 weeks, with the maximal effect by about 1 month and sustained reductions for 3 to 6 months or even longer if families change cleaning practices to remove food sources that will attract reinfestation. These practices include cleaning grease and other food debris from the kitchen, storing food in plastic containers or in a refrigerator, and eliminating food debris from the television room or bedroom. Even with household cleaning after extermination, cockroach allergen persists for months after successful pest control.
      Field trials of allergen reduction methods have shown that cockroach populations can be reduced by more than 90% in most cases,
      • Eggleston P.A.
      • Wood R.A.
      • Rand C.
      • Nixon W.J.
      • Chen P.H.
      • Luuk P.
      Removal of cockroach allergen from inner city homes.
      whereas allergen levels in settled dust and bedding decrease slowly over about 6 months. Although allergen might be completely eliminated from settled dust in less infested homes, in heavily contaminated areas, with Bla g 1 or Bla g 2 concentrations of greater than 100 U/g settled dust, treated rooms still contain allergen at levels that have been associated with disease. The first large field trial that included cockroach allergen control
      • Gergen P.J.
      • Mortimer K.M.
      • Eggleston P.A.
      • Rosenstreich D.
      • Mitchell H.
      • Ownby D.
      • et al.
      Results of the National Cooperative Inner City Asthma Study (NCICAS) environmental intervention to reduce cockroach allergen exposure in inner-city homes.
      found trivial reductions in cockroach allergen concentrations in treated homes. In a recently reported intervention that included integrated pest management, mattress and pillow encasings, HEPA room air filters, and HEPA-fitted vacuum cleaners in inner-city homes in 7 US cities, cockroach allergen Bla g 1 decreased by 44%, but initial concentrations only averaged 0.2 U/g; similar changes were seen in the control group, and therefore the net change was not significant.
      • Morgan W.J.
      • Crain E.F.
      • Gruchalla R.S.
      • O'Connor G.T.
      • Kattan M.
      • Evans II, R.
      • et al.
      Results of a home-based environmental intervention among urban children with asthma.
      Arbes et al
      • Arbes Jr., S.J.
      • Sever M.
      • Mehta J.
      • Gore J.C.
      • Schal C.
      • Vaughan B.
      • et al.
      Abatement of cockroach allergens (Bla g 1 and Bla g 2) in low-income urban housing: month 12 results.
      combined education, bait trap placement, and hydramethylnon gel bait placement with integrated pest management principles. They reported a 67% reduction of cockroach allergen in bedding and an even larger decrease in bedding; they commented that the careful placement of gel baits guided by inspection was essential to their success.

      Summary

      Effective methods of reducing most indoor allergens have been developed and tested. Each allergen source, house dust mites, pets, rodents, and cockroaches, requires a somewhat different approach, but currently recommended methods and readily available materials can reduce home exposures substantially.

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