Mites are a large group of arachnids, of great morphological and size diversity, which are present on all continents, except Antarctica. Some, like the tick, can measure several millimeters in length, while others, like the pyroglyphids, measure less than 500 microns.
Several species of this family appear frequently in house dust: Dermatophagoides culinae, d. farinae , D. microceras, d. pteronyssinus, D. Siboney and Euroglyphus maynei . They are the so-called dust mites, which usually cause allergies.
The life of a dust mite
Dust mite eggs hatch at any time. From birth, the mite goes through different larval stages before reaching adulthood. Depending on the environmental temperature, the development process can last from 15 days (at 35 °C) to four months (at 16 °C). The life cycle of the adult female lasts between two weeks and a month, and she lays between 30 and 70 eggs.
Adult mites feed on scales and dead skin debris , which are constantly shed from the human body, especially at night. Hence, mattresses, pillows and blankets are optimal habitats for dust mites.
Where does a mite have allergens?
Each species of dust mite produces several types of allergens, some common to all species and others specific to each species—except D. culinae and D. farinae , which produce the same—. There is not just one dust mite allergy , but several, one for each allergen . The same person may be sensitized to some and not to others. For this reason, some people allergic to dust mites do not always react to the presence of dust; Allergy only manifests when the species to which they are sensitive are present. However, the type of reaction is identical, in all cases.
In addition, there is a curious peculiarity, called cross-reactivity, which consists in the fact that a person who becomes sensitized to the allergens of one species can also become sensitized to other allergens without ever having been in contact with them. Specifically, this type of effect has been observed in people allergic to D. petronyssimus who, without contact with mites of the E. maynei species or, therefore, with their allergens, also had an allergy to them.
In total, 22 allergens have been identified in dust mites , most of them with a protein structure and, in many cases, of the proteolytic enzyme type —proteins that are responsible for breaking the peptide bonds of other proteins, and that are involved in their metabolism and in your digestion.
More than 80% of allergies to dust mites are triggered by two specific allergens: Der p 1 —a cysteine protease, responsible for cell digestion— and Der p 2 —a protein from the NPC2 family, related to the transport of cholesterol in the cell. In other words, most of the allergens from mites are common proteins, present in practically all the cells of these animals.
Some allergens are also present in mite faeces or are exuded through glands, and remain in the environment even after the mite is gone or even after death and decomposition.
How to deal with allergy to dust mites?
Like everything related to health, prevention is the best solution . All allergies arise from a first contact in which sensitization occurs. Also, once a person is sensitized, there are ways to prevent allergic reactions. In either case, preventive measures have three main goals: to reduce the mite population, to reduce allergen levels, and to reduce human exposure to any of them.
Maintaining a relative humidity below 50 % is one of the best recommendations to reduce the population of mites and their levels of allergens. Mites need high humidity to survive.
On the other hand, allergens are soluble in water, and mites cannot withstand high temperatures. Therefore, washing pillows and bedding at high temperatures – above 55°C – kills dust mites and removes all their allergens. Dry cleaning kills dust mites but does not remove allergens.
For possible shelters that cannot be washed, such as carpets or mattresses, it is best to use a vacuum with a high-efficiency particulate filter . Bagged vacuum cleaners are not recommended because dust can come out of the bag and spread allergens into the air.
Another very useful measure to reduce exposure to these mites is to use protective coverings and covers on mattresses and pillows, made with fabrics that allow perspiration, but prevent the passage of mites and their allergens. A study carried out in 1999 showed that feather pillows accumulated fewer allergens than synthetic ones, although this is most likely not due to the material they are made of, but to their lining: feather pillows have a much thicker coverage to prevent the feathers from coming out of the filling.
Of course, complete asepsis is not always possible. Sometimes, when cleaning, large amounts of dust are spread around the environment and end up being inhaled. In these situations, the best asset for the allergy sufferer is the mask , preferably with PM2.5 particles, or with an FFP2 or higher filter.
AAFA. 2015. Dust mite allergy. Asthma and Allergy Foundation of America.
Arlian, L. G. et al. 1990. Development of Dermatophagoides pteronyssinus (Acari: Pyroglyphidae). Journal of Medical Entomology, 27(6), 1035-1040. DOI: 10.1093/jmedent/27.6.1035
Arlian, L. G. et al. 2001. The biology of dust mites and the remediation of mite allergens in allergic disease. Journal of Allergy and Clinical Immunology, 107(3, Supplement), S406-S413. DOI: 10.1067/mai.2001.113670
Colloff, M. J. 1991. A review of biology and allergenicity of the house-dust mite Euroglyphus maynei (Acari: Pyroglyphidae). Experimental & Applied Acarology, 11(2), 177-198. DOI: 10.1007/BF01246090
Mari, A. et al. 2006. Allergome: a unifying platform. Works from the Paul Ehrlich Institute (Federal Office for Sera and Vaccines) in Frankfurt am Main, 95, 29-39; discussions 39-40.