Hofmann, Dietrich (1998)

On the assessment of the prevalence of keratin allergy

The number of studies on the increase in atopic diseases, especially in childhood, has risen over the last years. We can take as fact, that there has been a considerable rise in the frequency of diseases of the respiratory tract (such as asthma and hay fever) as well as in eczema rates (atopic dermatitis) (1). Whether it is correct, however, that the number of cases has almost doubled, as some scientists claim, may be disputed. We have to nevertheless estimate, that asthma prevalence amounts to almost 10% among children (2). Asthma occurrence in adults comes to more than 5% (4).

It is particularly from immunological research, that it has become increasingly evident over the past years, that allergic exposure is a key factor in the inflammatory reaction of the mucous membrane, which causes the symptoms to become chronic. In this context, beside feathers and down in bedding articles and the house dust mite, animal epithelia and mould fungi are particularly being discussed, especially under the present climatic conditions; animal epithelia and mould fungi having a protraction effect on the mucous membrane, as opposed to, say, pollen antigens. Lately however, some studies have been carried out, which induce us to consider feather allergies and the consequential diseases of the respiratory tract. The present expert opinion is aimed at this (7).

1. Immunological bases of atopic diseases

The clinical pictures of atopic diseases include an allergic disposition, which is marked by an increased IgE antibody production and genetic determination. The most frequent diseases, which will be discussed here, are atopic dermatitis (neurodermatitis, eczema), hay fever, bronchial asthma and allergic gastroenteropathy. The way in which a person is exposed to the allergens is decisive for the manifestation of the symptoms. In this context we can say that foodstuffs, as well as drugs and allergens which get into contact with the human skin, will first of all cause cutaneous diseases and possibly those of the stomach and intestinal mucosa; whereas inhalation allergens, that are being breathed in, are in most cases liable to generate allergic rhinopathy (hay fever) and bronchial asthma. Inquiring into the importance of bedfeathers in connection with allergic diseases, we need only consider the diseases of the respiratory mucosa (hay fever, asthma), as the manifestation of the symptoms of the remaining atopic diseases, which are caused by these allergens, is highly unlikely, and plays no essential role.

This is also true for other types of allergies. The atopic diseases belong to the so-called type I allergies, the most frequent allergic diseases of all. The type II allergic reaction consists of an interaction of different cells, and is generated by proteins, penetrating into the organism; it is of no importance in this context.

The type III allergy can basically be caused by bird feathers (allergic reactions against feathers of budgerigars and pigeons are known). Allergens penetrate into the organism via the respiratory tract, thus leading to disease reactions in the lung or in other organs, and can be controlled only by strictly adhering to exposure prophylaxis. This kind of allergy, however, is not known to be caused by bedfeathers, for, to generate the allergic reaction, prolonged exposure to the allergens and high allergen levels are a prerequisite for this type of reaction (allergic alveolitis). In the case of bedfeathers, this situation would at most be possible, if a person were to work in the filling sector, or something similar, in the bedfeather industry. For the remaining part of the population, this type of allergy is insignificant. To generate a type IV allergy (contact allergy), close and prolonged skin contact is necessary, an unlikely scenario in the case of bedfeathers. The so-called pseudo-allergies are for the most part allergic reactions to drugs and food preservatives; in this case, again, bedfeathers are of no relevance.

The type I allergic reaction is induced by contact with the mucosa of the lower and the upper respiratory tract. If a person is sensitized to the antigen in question, there will be an immediate immune response, which is characterized by swelling of the mucosa, mucus hypersecretion of variable viscosity and by mucosa edema, or rather, a spasm in the underlying muscular system. While this immediate response will subside without treatment after a short period of time, a delayed immediate response will follow about 8 to 16 hours later, which involves again reactions of the mucosa. In the second phase, a migration of inflammatory cells into the mucosa will take place, with the affected part of the respiratory system having become hypersensitive. In this situation of hypersensitivity, other stimuli, such as cold air, mist, exercise or psychological factors are sufficient to trigger a disease reaction. This means, that previously inhaled allergens will lead to a delayed reaction, which is synonymous with the disease becoming chronic. In particular, this is true for allergens, to which the mucosa are constantly exposed, such as house dust mite and mould fungi; bedfeathers (keratin) could basically act as a trigger, too. Hence, allergens act as key factors in the chronic development diseases, such as bronchial asthma or chronic rhinopathy.

2. Inhalative allergens

Beside pollen and animal epithelia, the most important inhalation allergens are house dust mite and mould fungi. It has been known for some years now, that house dust is composed of more than 50 different, in large parts only insignificantly allergen, varying substances, and that the main antigen source in the house dust consists of the different species of house dust mite. Rarer antigens, which should be listed as allergens, are bedfeathers and the decay products of cockroaches, bloodworms and fish moths. The latter need not be considered here. The present expert opinion is firstly concerned with bedfeathers and secondarily with the possibility of house dust mite biotopes, forming in feather and down filled quilts and pillows.

2.1 Bedfeathers

During the past years, scientists have succeeded in producing highly purified and standardized allergic test solutions. At the latest since that time it is evident, that the antigen contained in feathers plays an only marginal role in directly triggering allergy symptoms. In 1994, Linna et al. (5) found out, that more than 80% of the subjects which showed a positive reaction to feathers, did so as well to house dust mite dermatophagoides pteronyssinus. This induced the authors to conclude, that the test solutions provided at that time did not contain exclusively feather extracts but a considerable degree of house dust mite antigen as well. Immunologists in general did not obtain any stronger allergic reactions to feather antigen, i.e., a positive reaction to the skin-rubbing test or to inhalative provocation.

However, skin test reactions do not prove actual exposure to bedfeather allergen on the level of the mucosa. On the basis of the current literature and our experience, we can therefore conclude beyond doubt, that the bedfeather (keratin) antigen is generally not responsible for triggering respiratory conditions including hay fever, chronic allergic rhinopathy or bronchial asthma, as its allergen potential, which is usually tested as a combination of goose, duck and chicken feathers, is supposed to be minimal, or rather, infinitesimal. This finding, as well as reasons of cost cutting, has induced many immunologists to not testing for keratin antigen anymore. It has furthermore led to numerous recent publications, be it teaching materials or handbooks, in which the keratin antigen is rarely considered as an isolated source of allergies and, thus, a trigger of allergic diseases; this is, by the way, a worldwide phenomenon. Summarizing the above, we can say, that there is a worldwide consensus on the insignificance of keratin antigens, as far as their allergological aspect is concerned.

2.2 House dust mite as a contaminant of feather and down filled bedding

The different species of house dust mite account for the main antigen contained in house dust, the most common types being dermatophagoides pteronyssinus (the original house dust mite) as well as dermatophagoides farinae (flour mite). Elevated populations of other mite antigens might exist under singular and theoretical conditions, especially in rural areas, but from an general epidemiological point of view they are of minor relevance. House dust mite as such is made up of mite faeces and, even if much less meaningful in this context, dust particles developing after the decay of mite, which we will find in elevated numbers in the dust of bedding. This is due to the fact, that mite mainly feed on scales of human and animal skin and that they proliferate particularly well in a climate with temperatures above 30 ºC and a relative humidity above 55 %, conditions under which population numbers become a significant factor. In this context the existence of reservoirs, where mites reside undisturbed by vacuum cleaners or similar interferences, should be mentioned (material structure). All these factors combine in the best possible way in the bedroom climate. It is an interesting fact, that many materials, such as upholstery or other fabrics, are infested with house dust mite after a short period of time, so that even new houses and beds are severely infested almost immediately.

Mite should be discussed especially in the context of bedfeathers, as in important literature on treatment for house dust mite allergies, in teaching materials as well as in handbooks, you will find the stereotyped statement, that bedding articles containing feathers and down make up an excellent breeding ground for mite antigens, and that mite will find a particularly favorable climate for proliferation in older bedding materials.

Although from time to time some researchers have vehemently tried to overcome this stereotype (Jürgens, 6), it was only recently that some articles have been published in renowned medical journals, which must not go unnoticed and find their way into further medical education (7, 8, 9).

It is mainly Jürgens (6), who found out, that children's rooms are one of the most important mite habitats, for their room climate is conducive to mite growth, as they are generally not sufficiently aired and, above all, fitted with inadequate mattresses, which supply microclimatic conditions beneficial to mite infestation. According to Jürgens, in the bed, which is the most important factor in exposure prophylaxis, it is not the pillows or the quilts which are so much infested, if they are provided with particular additional encasings (10). In this regard, the studies by Wahn et al. (11) need to be taken into account, which show that consistent encasing of mattresses alone will already lead to a dramatic reduction in mite infestation of the homes and that, approximately 1 year after protecting the mattresses by polyurethane encasings, the measurable sensitivity of the patient's respiratory tract (hyperreactivity) diminished significantly.

Jürgens already demonstrated, that pillows and quilts containing feathers and down, are at any rate not particularly mite-infested. Out of a total of 192 dust samples from pillows, 78 % of the specimen proved to be mite-free, and the remaining 22 % showed infestation levels that low, they were categorized as permissible from an allergological point of view (less than 10 mites per 0.1 g of dust).

The test outcomes were similar for 41 quilts containing feathers and down. Thus, an additional encasing of older bedding reduces the risk of exposure until it is nearly inexistent. Kemp's conclusion (9), which was published in the respected British Medical Journal, that polyester-filled pillows display a significantly higher content of Der pI - the main substance contained in mite allergen - than pillows with feather fillings (the quotient was 3.5 to 8.5 feather-filled to polyester-filled pillows), is an important one. Kemp's study contradicts past research, according to which allergen particles in feather and down filled bedding articles become more easily airborne than those in synthetic pillows and that they are therefore more prone to be inhaled. Obviously, this statement appears to be of no meaning. Kemp's affirmations are supported by Strachan (7), who claims that asthma prevalence in children from households using feather bedding is lower than that in children sleeping on synthetic pillows. The authors clearly determine that eliminating feather and down bedding does not reduce asthma prevalence. According to the survey, this is particularly true for synthetic pillows, which bear a 2.7 times higher risk of causing severe asthma-related symptoms.

Of course, pets play an essential role, as they contribute to an increase in mite populations, aside from the individual sensitization to the single pet.

To recapitulate this study: the authors ascertain that especially synthetic bedding articles and pets significantly augment the risk of severe asthma. They explain that avoiding feather and down filled bedding has barely any effect on asthma occurrence in children. In 1997 Strachan (8) pointed out once more in the British Medical Journal, that particularly severe shortness of breath in children using feather and down filled bedding is substantially reduced, and that avoiding feather and down filled bedding articles should not be further recommended without any detailed prior research on the use and the potential infestation levels of feather bedding. Marks' (12) survey is an important contribution to this subject. He affirms that mite populations in the homes of Australian schoolchildren suffering from house dust mite allergy were no more elevated than mite populations in the control groups.

3. Conclusive assessment

On the grounds of the previous considerations and having evaluated recent publications in the pertinent field, we can state:

Bedfeather or keratin antigens, if considered as isolated source of antigen, play only a marginal role in triggering allergic diseases.
Bedding articles filled with feather and down do not act as reservoirs for especially elevated populations of house dust mite, synthetic bedding is infested at least to the same degree with dust mite.
Additional encasing of bedding articles will reduce mite concentrations to a point, where pillows and quilts are virtually mite free.
The bed is still to be regarded as the proper source of house dust mite infestation, with the mattresses containing the main habitat for dust mite. In this case, as well, encasing is necessary.
There are indications in the literature on allergology, that children sleeping on synthetic bedding suffer more often at least from severe asthma attacks. Furthermore, in comparison with feather and down-filled bedding, synthetic materials do not offer any palpable advantage in exposure prophylaxis.
Consequently, the recommendations to generally avoid feather and down filled quilts and pillows in bedrooms of patients suffering from a respiratory disorder, should not be published anymore in further medical education literature.

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4. Bibliographical references

Burr, M.L. et al: Changes in asthma prevalence: two surveys 15 years apart (1989). Arch. Dis. Child. 64, 1452-1456
Mutius E. v. et al: Prevalence of asthma and allergic disorders among children in united Germany (1992). BMJ. 305, 1395-1399
Reinhard, D.: Asthma bronchiale im Kindesalter (1996). Springer-Verlag Berlin- Heidelberg
Wettengel, R. et al: Asthma, medizinische und ökonomische Bedeutung einer Volkskrankheit (1994). EurMeCom, Stuttgart
Linna, O. et al: Immunilogic cross-reactivity between hen's feather and housedust-mite-allergen extracts (1994). Allergy 49, 795-796
Jürgens, H. W.: Hausstaubmilben und Bett (1992). Der Kinderarzt 23, 1884-1889
Strachan, D.P. et al: Home environment and severe asthma in adolescence: a population based case-control study (1995).
Strachan, D.P. et al: The risk of wheezing in children using feather pillows (1997)
Kemp, T.J. et al: House dust mite allergen in pillows. BMJ. 313, 916
Owen, S. et al: Control of house dust mite antigen in bedding (1990). The Lancet 335, 396-397
Ehnert, B. et al: Reducing domestic exposure to dust mite allergen reduce bronchial hyperactivity in sensitive children with asthma (1992)
Marks, G.B. et al: Mite allergen (Der pI) concentration in houses and its relation the presence and severity of asthma in a population of Sidney schoolchildren (1995). JACI 96, 441-448

On the assessment of the prevalence of keratin allergy: Summary

On the basis of recent findings in the field of allergic diseases, it has become more and more apparent during the past years, that bedfeathers are only marginal in triggering different types of allergies. Allergic diseases of the respiratory tract, such as asthma and hay fever, are not actually caused by the keratin contained in bedfeathers, but essentially by house dust mite.

From actual research it emerges beyond doubt, that it is not quilts and pillows filled with feather and down which harbor elevated quantities of house dust mite, but that synthetic materials contain at least the same amount of mite populations. Moreover, it became apparent, that additional encasing further lowered infestation levels and that, as a consequence to these measures, hypersensitivity of the respiratory mucosa receded, and the clinical picture improved.

Another important result obtained from research is that children, who use feather and down-free bedding, suffered severe asthma attacks more frequently and that therefore synthetic bedding does not offer any palpable advantages in exposure prophylaxis compared to feather and down bedding.

As a consequence of the above discussion we strongly recommend to reconsider the advice according to which allergy sufferers should eliminate feather and down filled quilts and pillows from their beds - as a first step toward allergy prevention. Allergyrelated modifications to the bedroom must first and foremost be aimed at the mattresses, as they contain elevated quanities of house dust mite antigen (Der pI), with encasing being a minimum requirement. Moreover, recommendations referring to carpeting in these rooms remain unvaried.