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.

Humidity levels In Phoenix, AZ  July 2016

Humidity levels Houston, Tx  August, 2016

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. 

For many years, residents of the shinny new master-planned communities of Mountain Park Ranch, The Foothills, and Club West in Ahwatukee had only one way in or out of their neighborhood, giving it the distinction of being called (not so fondly) the largest cul-de-sac in America. To get to work you had your choice of using either Chandler Blvd or Ray Road, two giant arms of a horse shoe-shaped loop, both with a million cars stopped at a million red lights, all trying to get to the interstate at the same time every morning and back to home and supper at the same time every evening.   This tedious, wearisome daily exercise in commuter angst was the one thing that made many homeowners seriously question the wisdom of moving to Ahwatukee.

Then Pecos Road opened up: Ten miles of four-lane heaven connecting the outer frontier of Ahwatukee to Interstate 10 with only three lights.   Like most residents of The Foothills or Clubwest, Pecos Road was my daily commute. I was greeted with hopeful sunrises over the East Valley each morning and contemplative sunsets over the Estrella Mountains and Gila River Indian Reservation in the evening.

I took up cycling 5 years ago (mid-life crisis or early onset dementia?) and like most of the local lycra-ed community trying their best to out-pedal old age, Pecos Road became my second home; the place for serious training when long intervals were needed or to join friends for group rides and the occasional kamikaze sprint at the roads end. On Pecos you could spread you wings and fly for miles.

In less than a year from now, all that will change and Pecos Road will be no more, replaced by a freeway that will provide a bypass route for an endless line of trucks plodding West or East on Interstate 10.

The passing of Pecos Road and the coming of the trucks was on my mind today when I read two articles in the Journal of Allergy, Asthma, and Immunology about the harmful effects of living close to a busy freeway.

The first: Inhalation of diesel exhaust and allergen alters human bronchial epithelium DNA methylation, presents evidence that exposure to diesel particles and common environmental allergens, such as pollen and mold, can alter the DNA of the lung.   This change can produce lasting effects on gene expression, cell function, and health. In other words, exposure to diesel particles can alter your DNA in such a way that you develop allergies or asthma, even if you, or your relatives, never had allergies before.

The number of people with allergies and asthma has increased significantly over the past several decades – a rise that has occurred almost exclusively in industrialized countries.   Since exposure to air pollution is one of the factors that characterizes life in the developed countries, the alteration of our DNA by diesel particles may be one of the mechanisms responsible for the world-wide asthma and allergy epidemic.

The second article, Traffic-related air pollution exposure is associated with allergic sensitization, asthma, and poor lung function in middle age, reports more bad news for communities planted close to major freeways.   Numerous studies have shown exposure to traffic-related air pollution to be associated with respiratory problems in children. This study, however, focused on the effect of air pollution on middle aged adults. The researchers concluded that even relatively low levels of air pollution during middle age is associated with increased risk of allergic sensitization, asthma, and diminished lung function.

The growing body of information documenting the harmful effects of traffic-related air pollution is certainly concerning to residents of any community located close to a major freeway. It doesn’t help that in Ahwatukee, these harmful health effects compound the growing sense of loss that many feel as they watch progress take away an old friend.

Brian Millhollon, MD

Phoenix is a wonderful place to live if you enjoy spending time out of doors.  However, there is a catch. The conditions that make for our predictable-practically-perfect weather (at least in the winter and spring) has also led to some serious air quality issues.

Every year the Arizona Department of Environmental Quality releases a number of high pollution advisories warning Arizonans that it may be unhealthy to venture out of doors, particularly if you have a medical condition such as asthma.  July and August show the highest number of “very unhealthy days”.  In fact in July 2013, there were seven “very unhealthy days” reported.

Over the next few posts, I will review some of the unique conditions that make up our Arizona environment and spend some time on the major components that make up the “poor air quality” reported by the Arizona Department of Environmental Quality

To begin, one thing is obvious: Phoenix is a desert.  Like most deserts, our climate is characterized by high pressure conditions that camps out over the region for extended periods of time resulting in warm (and hot!), dry, and generally clear conditions.   Half of the yearly rainfall occurs during the winter when brief pacific storms move through the region.   During the monsoon season, from July to September, moister from the south brings higher humidity and most of the remaining rainfall, often in the form of violent thunderstorms.

During late fall to early summer, high pressure sits over the region like a glass lid, repelling the volatile weather fronts that plaque much of the United States and keeping the interior toasty warm and dry.  What little wind does occur is generated by local temperature and elevation variations.  This, along with the extremely low humidity during this time of year, allows airborne particles -dust, pollutants, pollen-to drift in the atmosphere for a very long time rather than being cleaned away by rain or ocean breezes.

Conditions change somewhat during the second half of the summer when high pressure travels north a bit allowing monsoon moisture to move into the valley.  The increased volatility in the local wind patterns not only produces thunderstorms (and the hope of rain) but also massive dust storms.  These giant walls of dust can transport appreciable quantities of organic as well as inorganic material as they move across the valley.  Exposure to these clouds of organic bits of plants, mold and who-knows-what-else (think Maricopa feed lots) can trigger severe allergy and asthma attacks.  An analysis of material from dust storms in Tempe showed they contain an average of 11% organic material.

Although monsoon storms have the potential to bring rain and some clearing of the air, summer is the time when ozone becomes a problem. That will be the topic of my next post.