Health Risks of Dust Mite Allergens
Research has clearly demonstrated that dust mite allergen increases the risk of various health effects . Nearly all of this research has been performed in houses. Where concentrations of mite allergen in house dust are greater than approximately 2 micrograms allergen per gram of dust, susceptible people have a much higher risk of becoming sensitized to (i.e., have an allergic response to) dust mite allergen [1, 2]. Those who are sensitized to dust mite allergen have a several-fold increased risk of asthma . Mite allergens exacerbate allergic rhinitis (allergen-caused inflammation of the nasal tissues causing runny nose or congestion) and atopic dermatitis (allergen-caused inflammation of the skin resulting in rash and itching) . A National Academy of Science committee concluded that the evidence was sufficient to conclude that dust mite allergen caused development of the disease of asthma and caused exacerbation of asthma in those with asthma .
Given the strong evidence of the health risks of dust mite allergens, there have been many studies of the health benefits for various interventions designed to reduce dust mite allergen exposures. Three health studies reviewed included measures designed to reduce indoor humidity [4-6]. Two of three studies 5, 6] reported statistically significant health benefits as summarized in Table 3. In one of these studies the health benefits could have resulted from changes in bedding, removal of carpeting, and improved cleaning which were implemented at the same time as ventilation to reduce humidity . In another of these studies , the subjects moved to new houses which could have resulted in many environmental changes other than a reduction in indoor humidity; thus, the health benefits cannot be clearly attributed to reduced indoor humidity and associated reductions in dust mites. Given the small amount of data and that several other studies were unable to significantly reduce indoor humidity or dust mite levels [7-9], we must conclude that the health benefits of humidity reduction interventions designed to reduce indoor dust mites are not well documented.
In another section of this website, two studies are noted that found higher levels of dust mite allergen in homes with evaporative cooling [22, 29]. Two other studies have investigated the association of evaporative cooling of homes with health outcomes. Aldous et al.  followed lower respiratory illness in the first year of life of 936 infants from Tucson and reported a substantial increase in lower respiratory illness with wheeze in infants who resided in homes with evaporative cooling, after controlling for various potential confounding factors. The odds ratio was 1.8 with a 95% confidence interval of 1.1 to 3.0, so the findings were statistically significant. Prasad et al.  evaluated 190 patients, age 1-42, for sensitization to allergens. Thirty four percent of patients from homes with evaporative cooling were sensitized to dust mite allergen, compared to 18% from homes without evaporative cooling. In addition, 42% of patients from homes with evaporative cooling were sensitized to at least one mold allergen, compared to 19% from homes without evaporative coolers. Both findings were statistically significant.
2. Platts-Mills, T.A., Chapter 43. Allergens derived from arthropods and domestic animals., in Indoor air quality handbook, J.D. Spengler, J.M. Samet, and J.F. McCarthy, Editors. 2000, McGraw-Hill: New York.
3. Arlian, L.G. and T.A. Platts-Mills, The biology of dust mites and the remediation of mite allergens in allergic disease. J Allergy Clin Immunol, 2001. 107(3 Suppl): p. S406-13. https://dx.doi.org/10.1067/mai.2001.113670.
4. Warner, J.A., et al., Mechanical ventilation and high-efficiency vacuum cleaning: A combined strategy of mite and mite allergen reduction in the control of mite-sensitive asthma. J Allergy Clin Immunol, 2000. 105(1 Pt 1): p. 75-82. https://dx.doi.org/10.1016/s0091-6749(00)90181-7.
6. Harving, H., J. Korsgaard, and R. Dahl, Clinical efficacy of reduction in house-dust mite exposure in specially designed, mechanically ventilated "healthy" homes. Allergy, 1994b. 49(10): p. 866-70. https://dx.doi.org/10.1111/j.1398-9995.1994.tb00789.x.
7. Niven, R., et al., Attempting to control mite allergens with mechanical ventilation and dehumidification in British houses. J Allergy Clin Immunol, 1999. 103(5 Pt 1): p. 756-62. https://dx.doi.org/10.1016/s0091-6749(99)70416-1.
8. Crane, J., et al., A pilot study of the effect of mechanical ventilation and heat exchange on house-dust mites and Der p 1 in New Zealand homes. Allergy, 1998. 53(8): p. 755-62. https://dx.doi.org/10.1111/j.1398-9995.1998.tb03971.x.
9. Fletcher, A.M., et al., Reduction in humidity as a method of controlling mites and mite allergens: the use of mechanical ventilation in British domestic dwellings. Clin Exp Allergy, 1996. 26(9): p. 1051-6. https://dx.doi.org/10.1111/j.1365-2222.1996.tb00643.x.
10. Aldous, M.B., et al., Evaporative cooling and other home factors and lower respiratory tract illness during the first year of life. Group Health Medical Associates. Am J Epidemiol, 1996. 143(5): p. 423-30. https://dx.doi.org/10.1093/oxfordjournals.aje.a008762.
11. Prasad, C., et al., Effect of evaporative coolers on skin test reactivity to dust mites and molds in a desert environment. Allergy Asthma Proc, 2009. 30(6): p. 624-7. https://dx.doi.org/0.2500/aap.2009.30.3290.