The Consumer Reports magazine calls the home humidifier a "gift of moisture" and recommends it as a "healthy holiday gift." The scientific evidence seems to be against this recommendation however. Please see the articles in the reference section below for details.
A cross-sectional study of children 1 to 17 years of age living in Buffalo, New York examined the prevalence estimates of indoor and outdoor environmental risk factors for asthma. Significant environmental risk factors were presence of smokers in the household, humidifier or vaporizer use, chemical odors indoors, frequent truck traffic, and chemical odors outdoors.
Overall, smoking, pets, humidifier, and cockroaches were all significantly associated with asthma in the home.
The use of ventilation-air-conditioning systems (42%), personal humidifier or nebulizers (43%), dampness inside the houses were risk factors in people with positive fungi skin test reactivity.
In children with no history of wheezing, an increased risk of developing asthma was associated with a humidifier (relative risk [RR] = 1.7).
Multiple conditional logistic regression analysis showed that after personal susceptibility factors were controlled for, the following were independent risk factors for asthma:
- the mother's heavy smoking (odds ratio (OR) = 2.77)
- use of a humidifier in the child's room (OR = 1.89)
- the presence of an electric heating system in the home (OR = 2.27)
Up to 40% of the world's population has been diagnosed with an allergic disease. The most prevalent allergy is to house dust mites (http://buff.ly/1jSF5Y6). Humidifier use may increase the dust mite counts in the bedroom. Dust mites "drink" through their surface. In fact, the best measure for dust mite control is to decrease the air humidity to less than 50% (it works for mold control as well).
Unfortunately, humidifiers have just the opposite effect - they increase the air humidity and may promote dust mite growth. Dust mite exposure is one of the most significant environmental factors for development of asthma in children.
Dust mite allergen avoidance. The main allergen is in the dust mite feces. Use 3 control measures for 3-6 months to see an effect on the allergy symptoms (click to enlarge the image).
It is inadvisable to employ a home humidifier in the home of an asthmatic - AAAAI Ask the Expert.
Self-reported home environmental risk factors for childhood asthma: a cross-sectional study of children in Buffalo, New York. Lin S, Gomez MI, Hwang SA, Munsie JP, Fitzgerald EF. J Asthma. 2008 May;45(4):325-32.
Home environmental factors associated with asthma prevalence in two Buffalo inner-city neighborhoods. Lwebuga-Mukasa JS, Wojcik R, Dunn-Georgiou E, Johnson C. J Health Care Poor Underserved. 2002 May;13(2):214-28.
[Fungal spores in the environment of the asthmatic patient in a semi-desert area of Mexico].
[Article in Spanish]. Rev Alerg Mex. 2002 Jan-Feb;49(1):2-7.
Indoor risk factors for asthma in a prospective study of adolescents. McConnell R, Berhane K, Gilliland F, Islam T, Gauderman WJ, London SJ, Avol E, Rappaport EB, Margolis HG, Peters JM. Epidemiology. 2002 May;13(3):288-95.
Childhood asthma and indoor environmental risk factors. Infante-Rivard C. Am J Epidemiol. 1993 Apr 15;137(8):834-44.
Childhood asthma and the indoor environment. Dekker C, Dales R, Bartlett S, Brunekreef B, Zwanenburg H. Chest. 1991 Oct;100(4):922-6.
Humidifiers and Indoor Allergies | AAAAI http://buff.ly/WQisIe
Dust Mite Respiratory Allergy: current therapies http://buff.ly/1UwMMUJ - ALK PR company helped write the paper with 3 writers, open access.