Have you ever noticed that the more humid it is outside, the more likely you are to experience itchy eyes, a runny nose, and a scratchy throat? The relationship between humidity and allergens is complicated, but we have learned quite a bit over the years on just how these seemingly unrelated concepts intermingle.
With technology that allows us to control the humidity inside of our homes, we have already taken a crucial step toward alleviating these bothersome symptoms – it’s just a matter of what to do and why.
In this article, we are going to take an evidence-based approach in exploring how humidity affects the number of allergens in your home, as well as how this translates to the severity and frequency of allergy-based symptoms and conditions. Along the way, I will provide some recommendations on how you can make your living space allergen-free.
One of the most pivotal moments in allergy control occurred back in 1967 when Professor Voorhorst and his colleagues discovered dust mites to be the primary source of allergens in ordinary house dust. (R Voorhorst, 1967) Over the next several years, scientists noticed that dust mites had an undeniable preference for damp, muggy air.
Under closer inspection, the miniature bodies of dust mites are actually made up of about 75% water – with their survival highly dependent on maintaining this high-water content. In order to achieve this, dust mites actually absorb water vapor from the air! (Arlian L. , 1992)
A decade after Voorhorst’s study, a number of surveys conducted in temperate climates across the United States showed a direct link between the humidity of the air and the number of dust mites inside local homes. That is, the more humid the air in the house, the more dust mites were found to be lurking. (Lang JD, 1978) (Murray AB, 1979) (Platts-Mills TAE, 1986)
In direct contrast to this, homes located in drier climates had very low numbers of mites. Still not convinced? When moisture was added to the air of homes in these dry regions with an evaporative cooler, the number of mites in the houses spiked dramatically! (Ellingson AR, 1995)
Studies have demonstrated that the average dust mite will actually die from dehydration in as little as five to eleven days, provided the relative humidity within the environment is kept to 50% or less. (Arlian L. G., 1975) (RL Brandt, 1976) You read that correctly, scientists found that removing water from the air around these pests acted as a better exterminator than several actively toxic pesticides.
In fact, maintaining the relative humidity inside your house below 50% for the majority of the day has been proven to effectively prevent the growth of mite population and decrease allergens. (LG, JS, & DL, 1999)
One proven way to achieve a household humidity of less than 50%, regardless of which part of the world you live in, is by using a high-efficiency dehumidifier. These devices are a cost-effective and practical way to lower and maintain the humidity in your home, reducing mite and allergen levels over time. (Arlian, Alexander, Fowler, & et, 2000)
I recommend an average household humidity between 30% and 50% for ideal comfort and allergen control. You should keep in mind that it is not an issue if the relative humidity creeps over the 50% mark for a few hours a day, and you can also target the lower end of the suggested range to counteract this if you feel your average is too high. Relative humidity can be measured easily with a moisture meter, which can be bought for around ten dollars at any hardware store.
Dust mites are not alone in their ability to produce allergens, and far from the only allergens that thrive in humidity. In fact, increased moisture also promotes the growth of other known allergen producers, including many species of mold and fungus. (Singh & Jaiswal, 2013)
This question was brought to the forefront in the 1980s when doctors noted that asthma symptoms worsened when humidity increased in the ambient air of patients’ natural environment. (Korsgaard, 1983) Since then, these allergens have been linked as a major trigger for a number of allergen-induced conditions, including asthma and skin irritation, known as atopic dermatitis. Not only can allergens worsen symptoms of these conditions in the short term, but it has also been shown that full recovery from symptoms often doesn’t occur for several weeks after complete removal of a trigger from the environment. (Platts-Mills TA, 1997)
A majority of the evidence pertains to asthma, but that’s not surprising when you consider the World Health Organization (WHO) estimates that asthma may affect as many as 334 million people worldwide. (WHO, 2014) The chronic condition is characterized by recurring attacks of wheezing and difficulty breathing, a burden that dramatically impacts the quality of life of those affected. During an asthma attack, allergens in the environment cause the airways in the lungs to narrow, making it more difficult for air to move out of the lungs.
In 2009, a group in Scotland set out to determine how using a household dehumidifier over the course of a year may affect asthma and its symptoms. They reported that asthma patients with a dehumidifier in their home had an increased ability to breathe air out of their lungs in the evening compared to asthma patients living without a dehumidifier. (Wright GR, 2009) By reducing the amount of humidity in the air, there were fewer allergens in the environment, allowing the airways of asthmatics to stay open.
Based on the current evidence, long-term use of a household dehumidifier can decrease allergens in the environment known to trigger and acutely worsen the symptoms of asthma, but also other allergic diseases. Research shows that the room in which the dehumidifier is situated will experience the most substantial benefit in allergen reduction, so I recommend you run your dehumidifier in the bedroom during daytime hours to maximize air quality where you sleep. Since all dehumidifiers contain a compressor which will generate mild noise that may be disruptive for lighter sleepers, the best practice would then be to move the unit into another high-activity area of the house during the night. Not only will this dry and reduce allergen count in your bedroom for when you are ready for some symptom-free sleep, it will also lower allergen counts in your primary living areas for when you are awake and active throughout the day.
As mentioned before, several molds and fungi love to grow in humid places. While we’ve already discussed the implications of mold on allergen production, these molds are also a common cause for unpleasant “musty” odors emanating throughout your house. Molds, in the right conditions, can grow nearly anywhere – including carpets, wood, walls, and foods. The United States Environmental Protection Agency (EPA) are quick to note that the only way to regulate mold growth in your home is to tightly control the level of moisture in the air. (EPA, 2016)
The same dehumidifier guidelines apply for musty smells, with a 30-50% range adequate for prevention of mold growth and subsequent odors. Keep a close eye out for condensation, or water vapor on the walls or windows, as this is a worrisome indicator for high humidity. Quickly drying these surfaces and starting your dehumidifier can help to cease mold production.
Dehumidifiers come in a variety of sizes, and the right choice for you will depend on the size of the room and the amount of moisture you need to remove from your air, as measured by pints extracted per day. For smaller (500-1000 sq. feet), occasionally damp and musty rooms, 30 to 40-pint dehumidifiers will likely be sufficient. On the other hand, rooms larger than 2000 sq. feet that always have visible condensation may require 60 and up pint dehumidifiers.
There are many great options available when choosing the dehumidifier that’s the right fit for you and your home, whether you are looking for a dehumidifier for basement, living room, bedroom or a crawl-space dehumidifier.
Below are my recommended best dehumidifier options (easily available online at Walmart, Lowes, The Home Depot or Best Buy):
Best dehumidifier options for medium to large capacity dehumidifiers:
Best dehumidifier options for small to medium capacity dehumidifiers:
Dr. Peter Grossman earned his MD from the Virginia Tech Carilion School of Medicine, trained in Internal Medicine, and is now a full-time medical writer and consultant. He is a strong advocate of evidence-based medicine and its application in improving everyday life for patients.
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