It is monsoon season in Phoenix and the weather is hot and sticky. As uncomfortable as it may feel, the outdoor humidity level in Phoenix this time of year rarely exceeds 50% and the indoor humidity levels in the typical Phoenix home, with air conditioning running day and night, may average no more than 30-40%. These levels are still fairly low when compared with the dripping misery the residents of Houston, Mobile, or Chicago have to endure every summer, but significantly higher than the desiccating 21% average humidity in our winter and spring.
Why is this important for people with allergies? Many migrants to Phoenix from more humid lands do say that they feel better living in the dry, desert climate but most important from an allergy perspective, low humidity means no dust mites.
The House Dust Mite is the poster child for indoor allergies in many parts of the world. Innumerable numbers of these microscopic insects eat, grow, raise families, and poop in the part of the home were we spend most of our time, the bedroom. They like our beds because it provides a rich source of their favorite food: people dander. House Dust Mites feed on the dead skin scales (dander) than we leave behind while tossing and turning trying to get our 8-10 hours. After a zillion generations of living, eating, pooping, and dying in our beds, the accumulation of house dust mite related “material” in our mattresses, pillows, and comfy down comforters can be disgustingly rich. And all of this is allergenic.
House dust mite allergy is a major cause of allergic rhinitis and asthma and significant recourses have been directed at limiting our exposure to dust mite allergens in the home, including pillow and mattress covers, removing stuffed animals from the bedroom, pulling up carpeting and rugs, removing upholstered furniture, taking out venetian blinds, and (Say it ain’t so!) removing ceiling fans, to name a few. However in spite of all these disruptive and potentially expensive undertakings in the fight to control the lowly mite, the most effective deterrent by far has been to reduce indoor humidity.
Like most living things, House Dust Mites are mostly water and since they cannot go downstairs to get a drink of water when they get thirsty, they need to absorb moisture from the atmosphere. Many studies have shown that indoor humidity levels of around 75% are needed for dust mites to thrive.
Which brings me back to why humidity in Phoenix is an important allergy topic. I recently started monitoring the humidity level in my home with a hydrometer. This device keeps track of the current, low, and maximum humidity levels in the home year round.
This is a picture of the hydrometer’s current reading. The indoor humidity has stayed around 30-40% during our most humid time of year with a rare spike to just above 50% during a recent storm. These humidity levels are too low to support House Dust Mite growth.
Unseen monsters, particularly those as ugly as the House Dust Mite, are frequently blamed for our problems when the real cause is unknown, but when we are experiencing mystery allergy symptoms in the home, unless there is an indoor source of moisture, such as an evaporative cooler or a 500 gallon indoor aquarium or hot tub, a home may contain a lot of dust but not dust mites.