Regional Issues  
Prevalence of allergy and asthma in the Southwest

Moving to the Southwest for Health Reasons?  
Asthma / Respiratory allergy / Climate, mold and mites / Pollen /Air pollution 
 

Asthma 

• Asthma in some patients may improve after moving to smaller cities in the arid Southwest 
• Improvement may be from escaping high mold spore counts or high dust mite counts 
• Improvement may follow move from heavy polluted environment 
• Very severe asthma does not usually improve after moving: don’t move for this reason alone, particularly if you have established care from a competent asthma specialist.
• Some asthmatics may do better in Tucson than in Phoenix and Yuma, where mold counts  are higher. 
• Consider a trial period of several weeks in the area. 

Respiratory Allergy 

• Includes allergic rhinitis and asthma 
• Some very allergenic plants such as short ragweed and giant ragweed don’t grow in the Southwest, but their botanical relatives are well established here and cause symptoms in patients allergic to short and giant ragweed because of allergenic cross-reactivity with our local ragweed species such as Triangle-leaf Bursage.
• Many of the pollen-producing plants that grow in the Sonoran Desert are different from those in other regions
• Allergy can develop for the first time because of contact with pollen unique to the area, often after a "honeymoon" period of 12-18 months 
• Allergy testing to southwest allergens: delay for at least 12 months after moving 
• Allergy injection treatment for cold climate pollen: stop unless the move to the desert is temporary 

Climate, Mold and Mites 

• The Southwest is dry: only 10 inches of rain per year, most in the summer “monsoon” (June 15 - September 30).  The actual onset of the season varies from year to year, and depends in part on the dewpoint.
• For local information on climate see http://www.rssweather.com/climate/Arizona/Tucson/ and  http://www.rssweather.com/climate/Arizona/Phoenix/ links. 
• Additional information on the Arizona monsoon is at the Southwest Climate Change Network.
• Less cultivation and irrigation in rural areas keeps mold spore counts down 
• Humidity and airborne mold spores increase after summer rain 
• In homes with refrigerated air conditioning: house dust mites are less of a problem 
• House dust mites and other indoor allergens are more prevalent in evaporatively cooled homes due to higher indoor humidity 

Pollen 

• Maximum pollen counts are lower than in most other regions in the USA 
• Flowering periods are longer: pollen in the air almost year-round 
• Pollen counts are lowest in December, January and July (see Tucson Pollen Calendar) 
• Bermuda grass produces the most important allergenic pollen 
• Allergy to pollen from cool climate grasses does not cause allergy to Bermuda grass.  Many other grasses in the Southwest do crossreact with cool season grasses
• Allergy to unique pollen types in the Southwest usually takes at least a year to develop.  Allergy to the unique pollen can develop much faster if there is allergenic cross reactivity, i.e., similarity, between the unique Arizona pollen and a pollen type at the origin of the person moving (see Allergenic Pollen in the Southwest).                 

Air Pollution 

• Little heavy industry in Tucson: most pollution is from dust and motor vehicles 
• Phoenix has heavy pollution from vehicular traffic and Las Vegas expected to have similar problems soon 
• Tucson and Albuquerque are less polluted than larger cities (see  Air Pollution, Asthma and Allergy) 
   

Disclaimer:   This site is for educational purposes only.  Any information that you have found in this web site is not intended to replace medical care or advice given to you by your own physicians. You should consider consulting your local medical library and other web sites for additional information. 

Comments and suggestions welcome!   Email: schumach@u.arizona.edu
Content Owner:  Michael J. Schumacher, MB, FRACP, The University of Arizona

Updated 2/ 2012