Indoor Allergen Avoidance

Author: V. Dimov, M.D., Allergist/Immunologist and Assistant Professor at University of Chicago
Reviewer: S. Randhawa, M.D., Allergist/Immunologist and Assistant Professor at NSU

The word cloud of indoor allergens shows the frequency of term use in this article.

What is the strongest risk factor for asthma?

- sensitization to one or more of the major indoor allergens (dust mite, cat, dog, or cockroach, DCDC)
- accumulation of relevant allergens in the house

How the allergens change during the season: mnemonic TGR MI DC/DC ("a Tiger with an MI went to DC twice")

"There's spring time, where you have the tree pollen. Summer time, where you have the grass pollens. And then there's the fall time when you have the weed pollen.”

This sequence is remembered by the mnemonic TGR MI DC/DC ("a Tiger with an MI went to DC").

Pollen calendar: TGR MI DC/DC

Tree pollens
Grass pollens
Ragweed and weed pollen

Mold spores
Indoor allergens - DC/DC - Dog/Cat and Dust mite/Cockroach

Pollen-producing plants (weeds and trees) in Omaha, Nebraska


Characteristics of allergic sensitization among asthmatic adults older than 55 years: results from the National Health Allergy Season Year Round. WTOC-TV Savannah.
Interactive Allergy Map by Greer Labs. Click your state to find region-specific, common airborne allergens there.
‘Botanical sexism’ blamed for making life miserable for allergy sufferers as male trees fill city skies with pollen

Indoor allergens (click to enlarge the image).

The risk of house dust mite-sensitized children having current asthma doubles with every doubling of Der p I level.

Source: House dust mite allergens. A major risk factor for childhood asthma in Australia. Peat JK; Tovey E; Toelle BG; Haby MM; Gray EJ; Mahmic A; Woolcock AJ. Am J Respir Crit Care Med 1996 Jan;153(1):141-6.

Sensitivity to house dust mite and to cat dander are highly significant independent risk factors associated with the development of asthma, whereas grass sensitivity is not a significant independent risk factor for asthma.

Source: The relative risks of sensitivity to grass pollen, house dust mite and cat dander in the development of childhood asthma. Sears MR; Herbison GP; Holdaway MD; Hewitt CJ; Flannery EM; Silva PA. Clin Exp Allergy 1989 Jul;19(4):419-24.

Does a change in environment helps asthma symptoms?


The level of bronchial hyperreactivity and the percentage of eosinophils in sputum samples were evaluated in a group of asthmatic children allergic to house dust mite before and after a 3-month period of antigen avoidance in an Alpine environment. Antigen avoidance significantly reduced the eosinophil phase of airway inflammation, along with bronchial hyperresponsiveness.

Source: Influence of allergen avoidance on the eosinophil phase of airway inflammation in children with allergic asthma. Piacentini GL; Martinati L; Mingoni S; Boner AL. J Allergy Clin Immunol 1996 May;97(5):1079-84.

Allergic patients should reduce allergen exposure in their houses as part of the management of asthma and allergic rhinitis.

Dust mites (Dermatophagoides pteronyssinus and D. farinae) (Der p1, Der f1)

Yellow mite. Image source: Wikipedia, public domain.

Dust mites are arachnids that colonize bedding, sofas, carpets, and any woven material. Dust mites do not have eyes or antennae. They have 8 legs and a mouth-like appendage.

There are 2 different species:

- Dermatophagoides farinae is American HDM
- Dermatophagoides pteronyssinus is European HDM

The term arachnid is from the Greek word arachne, meaning spider, and also referring to the mythological figure Arachne.

Arachne was a great weaver. She boasted that her skill was greater than that of Athena the goddess of crafts, which resulted in a contest between her and the goddess. In the end the weaver won and the angry goddess turned Arachne into a spider.

Gustave Doré. Arachne (illustration to Dante's Purgatorio). Image source: Wikipedia, public domain

Dust mites do not bite and cannot be seen with a naked eye. The size of a HDM is 250-300 microns - 3 of them could fit inside the period at the end of this sentence.

Dust mites were first discovered by the inventor of the microscope, Anton van Leeuwenhoek. In 1694, Leeuwenhoek reported his discovery of microscopic "little animals" that live in dust.

What do mites drink?

They do not drink. Mites never drink but absorb humidity from the atmosphere, therefore they do not live optimally in dry environment. Dust mites are far less common in arid and high-altitude climates, such as the southwestern United States.

What do mites eat?

Mites feed on organic matter (shed human and animal skin particles) with the aid of fungal degradation.

"Dermatophagoides" means "skin eater."

Your mattress may contain between 100,000 and 10,000,000 dust mites.

During its 80-day lifespan, the average HDM produces about 1,000 fecal particles. A half teaspoon of dust contains 1,000 dust mites and 250,000 fecal particles.

Mite feces are a complex mixture of allergens:
- endotoxins
- enzymes
- mite and bacterial DNA

Der p 1 is a cysteine proteinase from feces of the HDM Dermatophagoides pteronyssinus.

Der p 1 elicits IgE antibody responses in patients with dust mite allergy. Der p 1 proteolytically cleaves the IL-2 receptor (CD25) on T cells which is involved in the homeostatic control of human IgE synthesis. Proteolytic activity of Der p 1 biases human CD4 and CD8 T cells towards a type 2 cytokine profile.

Source: Human T cell subset commitment determined by the intrinsic property of antigen: the proteolytic activity of the major mite allergen Der p 1 conditions T cells to produce more IL-4 and less IFN-gamma. Ghaemmaghami AM; Robins A; Gough L; Sewell HF; Shakib F. Eur J Immunol. 2001 Apr;31(4):1211-6.

House dust mite (HDM) feces are large and heavy (particles 6-10 micrometer in diameter) and are only transiently airborne.

Mite feces settle rapidly and are not detectable in the air within 15 minutes, therefore air filters have little role in controlling exposure.

Exposure to HDM occurs by close proximity to feces during time spent in bed, on the floor, or on upholstered furniture.

Measures to control HDM exposure

Dust mite allergen avoidance. The main allergen is in the dust mite feces. Use 3 control measures for 3-6 months to see an effect on the allergy symptoms (click to enlarge the image).

Dust Mite Control (click to enlarge the image).

Physical barriers


- pillows
- mattresses
- box springs
- comforters
- furniture cushions

The simplest covers are made of plastic but they may be uncomfortable to use.

Gas permeable fabrics are an alternative to plastic covers.

Woven fabrics with a pore size of 6 microns block the passage of mites. Woven fabrics are preferable to non-woven materials which can retain high levels of allergen on the surface and lose integrity with repeated washing.

Benefit of bedding covers (as only intervention) on asthma control has not been well-documented

Minimizing reservoirs:

- fabric and carpets
- upholstery and drapes

Remove carpets, upholstered furniture and drapes.

Vacuuming floors using a high-efficiency particular air (HEPA) filter.

Remove stuffed toys from bedroom.

Decrease humidity to below 50%

Decreasing humidity to below 50% reduces mite growth.

Best method: air conditioning in a humid climate.

Do not use humidifiers. Use dehumidifiers. Use saline nasal spray for dry nasal passages.

Upper floors are less humid. Patients allergic to HDM have less symptoms on 2nd floor.

Lower floor carpets often remain damp and become a rich source of bacterial, fungal, and dust mite allergens

Upper floor apartments have much less humidity than houses and 10-times less mite allergen.

Heat treatment of bedding

After washing, bedding should be dried in a dryer on a hot setting.

Insecticides are not useful.

Impact on asthma control was not consistent in studies due to confounding variables:

In 50% of the reported trials, dust mite avoidance failed -- the measures did not decrease allergen exposure for a significant period of time.

You need at least 3 methods for 3 months minimum:

Physical measures for 3-6 months:

- pillow covers
- mattress covers
- washing bedding in hot water/dryer
- carpet removal

Bed covers reduce exposure to dust mite and improve adult atopic asthma

Pet Allergens

Best solution: Do not to keep animals in the house.

Animal Dander Avoidance (click to enlarge the image).

What is the source of animal allergens?

Scales shed from the animal's skin (similar to human dander).

Restricting the animal to one part of the house is ineffective. For example, cat allergens are easily carried on clothing. Fewer than 50% of cat-allergic individuals report direct cat exposure (at home or elsewhere) (JACI, 2012).

Both cat (Fel d 1) and dog allergens (Can f 1) are small in size (different from HDM) and remain airborne for extended periods.

Many pet owner refuse to give away their animals. In this all too common scenario, allergen control can be attempted but is not very effective.

Even when a cat is removed from the house, allergens persist for weeks to months.

This explains why when a cat-allergic patient moves into a home in which a cat was previously living, he/she may have more symptoms.

Cat allergen is transferred on clothing and can be detected in schools and houses without a cat.

HEPA Air filters to reduce the concentration of airborne animal allergens

Unclear effect. Aggressive cleaning with HEPA filter vacuum may help.

In a 2001 Pediatrics study, HEPA Air Cleaners Were Not Very Effective For Decreasing Visits and Asthma Symptoms in Children Exposed to Tobacco Smoke.

Bathing pets

Washing cats weekly or less often does not improve symptoms. In any case, cat allergen in the air returns to pre-bath levels in 24 hours.

Washing dogs twice weekly may be helpful.

"Hypoallergenic cat"

Majority of people with cat allergy are sensitized to the Fel d 1 protein. A "hypoallergenic cat" ($4000 per cat) was developed (Allerca®) by breeding cats that were deficient in Fel d 1.

Initial studies showed fewer symptoms but allergen measurements were not published.

Rodents (mice and rats) (MUP)

Wood mouse, Apodemus sylvaticus. Image source: Wikipedia, public domain.

Rodents produce urinary proteins that are allergenic - mouse urinary protein (MUP).

Allergy to rodents in the workplace is an occupational health problem affecting research, pharmaceutical and toxicological sectors (Allergy to rodents: an update. Clin Exp Allergy. 2010 Sep. Mouse allergens are detectable in nearly all inner-city homes and in 75% of suburban homes. Allergen levels in inner-city homes are 100-1000-fold higher.

Exposure of infants to mouse allergens has been associated with the development of asthma, independent of other factors.

Control measures: extermination.

Cockroach (Bla g 1-4, Per a 1)

Female Blatella germanica with ootheca. Image source: Wikipedia, public domain.

Control measures: multiple baited traps with poison.

HEPA Air filtration is not helpful because the allergen settles quickly and does not remain airborne (similar to HDM).

Reducing exposure to cockroach allergen alone is unsuccessful because patients living in poor conditions are exposed to high levels of multiple allergens.

A combined strategy which reduces exposure to cockroach, mite and fungi is more successful.

Exposure to cockroach is linked to high shrimp IgE with questionable clinical reactivity - food challenge is needed for diagnosis (JACI, 2011).

Asian ladybugs (Harmonia axyridis)

Asian ladybugs were imported to the U.S. to control plant lice (aphids).

Asian Ladybug. Image source: Wikipedia, Creative Commons Attribution ShareAlike 2.5, Bruce Marlin,

Aphids (plant lice). Image source: Wikipedia, GNU Free Documentation License.

It was anticipated that the insects would not survive the winter but they did by invading houses.

Asian ladybugs may cause seasonal indoor symptoms - chronic cough, rhinitis, and asthma.

Ladybug hemolymph is the primary source of allergens - Har a 1 and Har a 2. 'Reflex bleeding' from tibiofemoral joints (for communication and during alarm) disperses these allergens. Specific IgE immunoassays are not yet available.

Control measures:

- treatment of the outside of a house with pyrethroid before the cold weather
- move to a tightly-built house or into an urban area

Indoor molds

Moldy nectarines that were in a refrigerator. Image source: Wikipedia, GNU Free Documentation License.

Indoor molds affect homes with high humidity.

The 4 common allergenic molds include AAHP (Alternaria, Aspergillus, Hormodendrum, Penicillium).

Indoor mold remediation is beneficial in patients with asthma and visible home mold growth regardless of patient's sensitivity to the 4 common allergenic molds (AAHP) by skin prick testing. Medication use decreased 41% in the intervention group, and increased 17% in the control patients.

Why patients not sensitized to the 4 tested molds (AAHP) benefit?

Because of decrease in mycotoxins and volatile irritants released by growing molds.

Control measures:

- remove of existing mold
- decrease humidity below 50%

Regarding the mold/asthma link, certain findings have been found consistently: 1. the mold has to be visible, 2. the mold has to be in the room where they live, 3. the patient does not have to be allergic to mold to have symptoms because the some molds release irritant volatile compounds in the air.

Outdoor pollens: Prevention

Keep windows closed
Use air conditioning at home and in the car
Minimize early morning activity (5-10 AM) when pollen is usually emitted
Stay indoors when humidity is high or on windy days
Shower and change clothes following outdoor activity to remove pollen from hair, skin, clothing
Avoid locations likely to have high levels of pollens: fields, woods, etc.
Do not mow lawn or rake leaves


Indoor Allergen Avoidance. Thomas A.E. Platts-Mills, MD, PhD. UpToDate, 16.2.
A Closer Look at Dust Mites. Achoo Allergy.

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Published: 11/01/2008
Updated: 04/15/2012

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