References: Dehumidification

These citations on the effect dehumidifiers and air conditioners on reducing mite allergen exposure are provided for allergists and other medical professionals. A full understanding of the role of dehumidification in allergen avoidance requires a critical reading of the complete text of these and other studies on allergen-avoidance, building science, indoor allergens including dust mites and mold, and allergic conditions including asthma, allergic rhinitis, and atopic dermatitis.

Reducing relative humidity to control the house dust mite Dermatophagoides farinae.

AUTHORS: Arlian LG; Neal JS; Vyszenski-Moher DL

AUTHOR AFFILIATION: Department of Biological Sciences, Wright State University, Dayton, Ohio 45435-0001, USA.

SOURCE: Journal of Allergy and Clinical Immunology 1999 Oct; 104(4 Pt 1): 852-6

CITATION IDS: PMID: 10518832 UI: 99449684



Indoor relative humidity (RH) is the key factor that determines the survival and population development of the house dust mite Dermatophagoides farinae. Maintaining RH below 50% is one recommendation in a comprehensive plan to reduce house dust mites and mite allergen levels in homes. Even when mean daily RH is reduced below 50%, RH may rise above 50% intermittently for brief periods because of activities in the home (eg, cooking, bathing, and ventilation).


The purpose of this study was to determine how brief daily periods of moist air alternating with long spells of low ambient RH (0% or 35%) influence population survival and growth of D farinae.


Population growth was determined for D farinae at daily RH regimens of 2, 4, 6, and 8 hours at 75% or 85% RH alternating with 22, 20, 18, and 16 hours at 0% or 35% RH.


D farinae populations declined at daily regimens of 2 hours at 75% or 85% RH alternating with 22 hours at 0% or 35% RH. Daily regimens of 4, 6, and 8 hours at 75% RH alternating with 20, 18, and 16 hours, respectively, at 35% RH provided sufficient moisture for small growths in population size. These growths after 10 weeks were reduced by 98.2%, 98.0%, and 97.3% for daily regimens of 4, 6, and 8 hours, respectively, at 75% RH (with the remainder of the day at 35% RH) compared with the growth of populations continuously exposed to 75% RH. Continuous exposure to 85% RH inhibited population growth, but alternating daily regimens of 16, 18, and 20 hours at 35% RH allowed small populations to develop, although they were reduced by 99.4%, 98.8%, and 99.1% compared with population growth at a continuous 75%RH. CONCLUSIONS: This study indicates that maintaining mean daily RH below 50%, even when RH rises above 50% for 2 to 8 hours daily, effectively restricts population growth of these mites and thus the production of allergen. To completely prevent population growth of D farinae, RH must be maintained below 35% for at least 22 hours per day when the daily RH is 75% or 85% for the remainder of the day.

The effects of season, climate, and air-conditioning on the prevalence of Dermatophagoides mite allergens in household dust.

AUTHORS: Lintner TJ; Brame KA

AUTHOR AFFILIATION: Vespa Laboratories, Inc., Spring Mills, PA 16785.

SOURCE: Journal of Allergy and Clinical Immunology. 1993 Apr; 91(4): 862-7

CITATION IDS: PMID: 8473674 UI: 93232476



Clinical evidence reveals a strong relationship between dust mite allergen levels and asthma. This study suggests the relative importance and interactions among factors that influence mite allergen levels in human dwellings.


Dermatophagoides pteronyssinus allergen (Der p 1) and D. farinae allergen (Der f 1) were measured in 536 dust samples collected from 424 homes across the United States.


There were distinct seasonal fluctuations of Der p 1 and Der f 1. Der p 1 rapidly increased to peak in July then gradually decreased through October. Der f 1 slowly rose to peak later, around September, before declining. Different climates in regions of the United States had no significant effect on the quantity of Der p 1 or Der f 1. However, regional climate differences seemed to influence the prevalence of either D. pteronyssinus or D. farinae. Air-conditioning significantly reduced (p<0.0001) Der 1 mite allergens detected in the dust samples, and a tendency existed for Der f 1 to be higher than Der p 1 in air-conditioned homes. There was a significant (p<0.01) interaction between air-conditioning and seasons. The most dramatic effect was observed during the summer months, the cooling season, from approximately May to September.


These findings show that distinct seasonal fluctuations exist of D. pteronyssinus and D. farinae mite populations, and suggest that differences in the microclimate within homes may have a dramatic effect on Dermatophagoides mite populations.

Water balance and humidity requirements of house dust mites.


SOURCE: Exp Appl Acarol. 1992 Nov;16(1-2):15-35

Summary: Dust mites die after 6 to 11 days at a relative humidity of 50% or less.  However, even above 50% relative humidity, the lower the humidity the less the reproduction and allergen production of dust mites.

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