Guest guest Posted December 11, 2007 Report Share Posted December 11, 2007 Sue, The doc quoted in the article said there is " no evidence that he knows of that humidifying air reduces colds " but there are papers that show that comfortable levels of RH can reduce respiratory and other symptoms: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1474709 " Indirect health effects of relative humidity in indoor environments " " A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have shown that the survival or infectivity of these organisms is minimized by exposure to relative humidities between 40 and 70%. Nine epidemiological studies examined the relationship between the number of respiratory infections or absenteeism and the relative humidity of the office, residence, or school. The incidence of absenteeism or respiratory infections was found to be lower among people working or living in environments with mid-range versus low or high relative humidities. The indoor size of allergenic mite and fungal populations is directly dependent upon the relative humidity. Mite populations are minimized when the relative humidity is below 50% and reach a maximum size at 80% relative humidity. Most species of fungi cannot grow unless the relative humidity exceeds 60%. Relative humidity also affects the rate of offgassing of formaldehyde from indoor building materials, the rate of formation of acids and salts from sulfur and nitrogen dioxide, and the rate of formation of ozone. The influence of relative humidity on the abundance of allergens, pathogens, and noxious chemicals suggests that indoor relative humidity levels should be considered as a factor of indoor air quality. The majority of adverse health effects caused by relative humidity would be minimized by maintaining indoor levels between 40 and 60%. This would require humidification during winter in areas with cold winter climates. Humidification should preferably use evaporative or steam humidifiers, as cool mist humidifiers can disseminate aerosols contaminated with allergens. " IMPORTANT NOTE: The authors are INCORRECT about evaporative humidifiers as portable units are generally NOT safe to use. I have investigated many and ALL contained microbiological growth (bacteria and often significant mold colonization). The most imoprtant thing to keep in mind is that you MUST monitor the RH with a hygrometer. If it gets much over 40% in winter, condensation and other problems may occur. Then the RH has to be lowered. Also keep in mind that the maximum safe indoor RH is also affected by the outdoor temperature. When it is extremely cold out, the maximum safe indoor RH may be 30% or less; otherwise there will be excessive condensation. One reason I chose 35% for the article is because most inexpensive hygrometers are off by +/- 5%. But 40% RH is OK so long as there is not excessive condensation. (Measure the RH in a cold, exterior corner at the floor/wall intersection and if the RH is over 75%, you may develop a mold problem.) Warm-mist humidifiers (except for the scalding issue) are the ONLY safe type of humidifier to use. These mix room air with the steam. Also, do not use a portable humidifier unless it has a humidistat (e.g. Honeywell QuickSteam). Do not use old-fashioned steam humidifiers that just boil water without any controls. C. May, M.A., CIAQP Re: Does using humidifers in the winter spread mold, bacteria? > Posted by: " ssr3351@... " ssr3351@... ssr3351 > Date: Mon Dec 10, 2007 9:54 am ((PST)) > > > Wow! I thought 35% was pretty low and always thought RH should be 50 or > below. Right now ours seems to be running between 35 to 38 %. Older people (like > my mother) always said to run a humidifier in the winter so the furniture > doesn't dry out but what did they do years ago without them?! Did the house and > furniture dry out and fall apart? > > Sue > Quote Link to comment Share on other sites More sharing options...
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