Jürgens, Hans W. (1992)

Prof. Dr. Dr. Hans W. Jürgens, Forschungsgruppe Industrieanthropologie, Neue Universität, Kiel

“The House Dust Mite Allergy and Down Blankets”

The current public discussion regarding allergies due to mites has acquired nothing short of neurotic characteristics. The impartial consumer gets the impression that a new epidemic, almost comparable to AIDS, has arrived to terrorize mankind and that everything possible must be done to control this new development.

The peculiar thing about this hysterical discussion is that allergies themselves are not held responsible for the public nightmare. Allergic diseases have existed for a long time. Even our ancestors suffered from common allergies such as hay fever, asthma, and others. The present public anxiety as represented in the media however, is not so much a reaction to the phenomenon of allergies in general, but rather focuses on one particular allergen, the house dust mite. With the help of the electron microscope, magnified horror visions of the house dust mite are produced. As these photographs are propagated through the media, a common public goal is generated; to pay attention and take action.

  1. Epidemiological studies have shown that among allergy causing agents mildew and fungus are the most common representing 30% of all allergens. Mildew and fungus are followed by flour, baking ingredients, additives, food products, pollen, and dust, with dust responsible for approximately 8% of all allergies. Due to the fact that approximately 20% of the general population can clearly be defined as allergic, and approximately 15% described as questionably allergic, the values quoted above should each be divided by 5 to accurately represent their distribution within the general population.

    Allergic diseases appear to be on the increase. Several reasons are offered for this development. Improved diagnostic techniques in association with more frequent visits to the doctor and the general tendency not to tolerate minor physical discomfort, to label such discomfort as ,,abnormal", and to view and treat it as an illness, could provide one explanation for more reported allergies. Further, increases in the levels of air contaminants and pollutants could also be associated with objective increases in allergic diseases.
  2. One is left with the impression that it is absolutely necessary to create a mite-free environment. The mite must be eradicated. For someone who knows something about the topic, it is obviously clearly impossible to create a mite-free environment for human beings living under normal conditions. Mites are even found in the clothing of hospital personnel. The only possibility is to decrease or to temporarily greatly reduce mite concentrations which would also considerably lessen the general quality of the living environment. It should also be recognized that a temporary elimination of mites would have little or no effect on the frequency of mite related allergies due to the fact that it is not the mites themselves which act as the allergen, but rather mite excreta which can remain active for an extended period of time even in an environment temporarily free of mites.

    The question "eradicate mites yes, no, or how?" is an inappropriate starting point for our discussion. Depending on the particular study quoted, only 1 to 5% of the general population reacts allergically to mite excreta. Although allergies related to pollen are much more common, no one would consider eliminating the birch-tree, destroying all grass, or uprooting other ,,dangerous" plants.Therefore, it can be concluded that the goal of mite eradication is an illusion. The only possibility is to reduce mite densities and to search for alternative ways to prevent allergic reactions in general.
  3. Previous studies aimed at determining areas of mite concentration have focused an the investigation of households. These studies, however, were seldom conducted under scientifically impartial conditions. More often they were carried out under commission of a partial party and far this reason, without intentional falsification, a particular emphasis was placed an the results. A summary of previous research provides the fallowing information regarding the environmental conditions most conducive to mite habitation. Mites live where:

    - they can be efficiently nourished with human or animal skin scales;

    - the thermal environment is between 17° and 32° C;

    - the humidity conditions are favorable above 55%;

    - they are provided with an area of protection, for example an rough surfaces with dust accumulation.
  4. Although house dust mites are found wide, regional differences exist in terms of their frequency. In this connection it is important to recognize the significant role played by seasonal Variation and the associated fluctuating values for temperature and humidity. Equally important are factors related to personal living habits such as manner and intensity of heating, ventilation efficiency etc. For these reasons regional differences found far the relative density of mite colonization as, for example, the frequently mentioned north-south gradient, are best interpreted as reflecting differences in personal lifestyle rather than global climatic or geographic phenomenon. In association with geographic differentiation, our studies, which have been carried out on areas from the North and Baltic Sea coastal regions to Austria, have shown that despite geographic differences in environmental humidity related to climate and elevation, external humidity can be easily compensated for within the household through proper heating and ventilation. For this reason regional differences in house mite density can be viewed as a controllable phenomenon.

    In this connection it is important to mention that unlike ants, which actively migrate and seek out appropriate environments for habitation, mites are passively transported to living environments, most commonly on clothing.
  5. Based upon the results of previous studies as well as on our own preliminary investigations we did not expect to find substantial amounts of house mites in blankets filled with feathers and down. The results of our investigations, were surprising, even in this light. A total of 602 feather, down, and textile samples taken from blankets and pillows were examined. The samples were taken from blankets and pillows which, after normal periods of use, were due to be professionally cleaned and provided to us with the cooperation of public health and government authorities in Schleswig-Holstein, Rheinland-Pfalz, Ingolstadt, and the extended areas of Berlin, Stuttgart, and Vienna, Austria. For a sample group of this size, a combination procedure including both ACAREX testing and microscope observation proved to be the most appropriate method for testing house dust allergen content and mite contamination. The combined procedure provided essential data concerning allergen concentrations as well as information related to the extent of house mite contamination and species identification.

    Analysis Results for Blankets:
    Of the 410 samples analyzed 98% showed negative results for mite allergin content and mite contamination. In the remaining 2% of the cases slight contamination was found although in all of these cases, the allergen content measured was clearly under allergy relevant levels.

    Analysis Results for Pillows:
    In 78% of the samples taken from pillows negative results were found for house dust allergen content and mite contamination. In the remaining 22% of the cases slight contamination was found although these results proved to be insignificant for both allergens and mite density.

    The differences found between the blanket and pillow samples and the tendency towards slightly higher levels in pillows is considered to be a reflection of the different ways blankets and pillows are used and ventilated which produces microclimatic conditions more or less conducive to mite habitation.

    In response to the clear results obtained from the representative field study it appeared necessary to further differentiate the results by means of an additional test. Supplemental Test: Feather and Down Blankets with Deficiency in Hygiene.

    In this particular subtest samples taken from 41 blankets including feather and down as well as sections of bedtick were analyzed. The requirement for inclusion in the sample was an obviously unusual deficiency in hygiene 1 and/or a total of 15-18 years without cleaning. lt is recommended to have blankets cleaned every 5 to 8 years, therefore, the samples included in the study were taken from blankets which exceeded the usual cleaning interval by 10 years or more. This test was designed to determine whether extreme deficiency in hygiene results in increased allergens and mite density, and which bedding components, feathers/down, or bedtick are most susceptible to mite contamination under these circumstances. Positive results for allergens and mite contamination in feathers or down were found in 6 cases and in 24 cases positive values were found for bedticks. However, as was the case in the previous investigations, these values were well beneath established allergy relevant levels.
  6. Of particular interest is the question concerning the possible causes for mite contamination in down blankets. In general it should be emphasized that mites do not actively seek out living environments but rather are transfered to them passively.

    To investigate this question, we repeated previously conducted studies where new blankets with various down fillings were placed in households defined as extremely mite contaminated. After an 8 week period in 12 mite contaminated households, it was found that although the environments remained strongly mite infested, the new blankets were not inhabited during this time period.

    Once it was determined that mites do not actively migrate to feather blankets, a research design was set up to stimulate mite migration through the manipulation of light and thermal conditions. In this series of investigations we could clearly show that although mites can easily penetrate the cotton material used in mattress 1 coverings, the bedtick samples in direct body contact were not penetrated. As a result, down blankets proved to be practically mite proof.
  7. The results of the studies conducted up to this point have demonstrated that although house mites remain an important problem for sufferers of mite related allergies, it is essential to view the situation within the boundaries of objectivity. Further, it is necessary to recognize that the complete eradication of mites in normal human living environments is not only infeasible, but would reduce the general quality of the living environment and have negative consequences for health. Therefore, the only appropriate approach to mite control is to reduce mite densities to allergy irrelevant levels. In this connection proper climatic control of warmth and humidity play a particularly important role in household mite management.

    The current public outcry and media propagated ,crusade against mites" is in any case inappropriate. Mites are by no means a problem of specific environmental factors and are certainly not a problem of any particular textile or material. The interdependent relationship existing between human physiology, climatic conditions, and the design of the bed situation produces conditions either conducive or deterrent to mite habitation. Here, additional factors such as heating, ventilation, and bed provisions, for example the still popular ,,day blanket", are extremely influential yet in general it can be concluded that within the presently available possibilities, the climatic conditions found under down blankets are particularly favourable for controlling the risk of mite contamination.


Prof. Dr. Dr. Hans W. Jürgens, Grupo de Investigação de Antropologia Industrial, Universidade Nova, Kiel

Resumo alemão do estudo:

„Análises ecológicas acerca da alergia ao ácaro do pó da casa”

Custuma ser apontada uma relação entre o aparecimento de reacções alérgicas ao ácaro do pó da casa e a utilização de roupa de cama com penas ou penugem. De um modo geral, muitos médicos e especialistas da indústria têxtil recomendam aos doentes e aos clientes com propensão para alergias a troca desses artigos por outros com materiais de enchimento diferentes. Devido aos novos resultados de exames científicos, este preconceito sobre as popriedades negativas de roupa de cama à base de penas e penugens tem de ser revisto ou, até mesmo, invertido.

Tendo em conta as investigações representativas levadas a cabo na Europa Central, nas quais foram analisadas centenas de habitações, quartos de cama, camas, edredões e almofadas em relação à infestação de ácaros do pó da casa e à concentração de alergénios, pode constatar-se o seguinte:

Os edredões e as almofadas de penas não são um domicílio preferido para ácaros do pó da casa. No interior destes artigos de cama, não se encontram quase nenhuns ácaros, se forem tidos os cuidados normais, uma vez que o tecido de revestimento com textura apertada representa uma barreira quase intransponível para estes bichos.

As condições térmicas e climatéricas que os edredões de penas proporcionam aos seres humanos (aquecimento rápido durante o sono, desumidificação rápida durante o arejamento) não os tornam num local preferencial para os ácaros que dependem da humidade.

Em cada habitação e em cada quarto de dormir existem quase inevitavelmente ácaros do pó da casa. Eles alimentam-se directamente das escamas minúsculas da pele humana, que cada um perde constante e inevitavelmente. Em contrapartida, as penas e as penugens não fazem parte da alimentação dos ácaros. Resumindo, pode portanto constatar-se o seguinte:

As abrangentes análises ecológicas e científicas acerca do aparecimento e alastramento de ácaros do pó da casa em todas as zonas climáticas da Europa mostram claramente que os edredões de penas e penugens não constituem, nem domicílio, nem fonte de alimentação para os ácaros do pó da casa. Por este motivo, não existem motivos científicos ou práticos para recomendar evitar o uso de edredões de penas ou penugem a um doente alérgico aos ácaros do pó da casa.