What are the aeroallergens in Tucson?


by Kundagal Murthy, M.D.

If you were allergic to pollen before coming to Tucson, the chances are your allergies became worse after your move. The incidence of allergies in Tucson is about twice the average incidence for our country. Even by conservative estimates it appears that one person out of every five has allergic symptoms. The increased incidence of allergies can be attributed to the increased pollen from trees, weeds, and grasses.

Tucson is one of the very few places where records of pollen counts have been kept for many years. The records over the five decades starting in the 1940s indicate that the pollen counts have increased disproportionately to the increase in population. This increase is due to the fact that plants were brought to this desert from other parts of the country, and also to the landscaping preferences of the people. Native ragweed and other weeds have also contributed to the problem. Mild temperatures and sunshine throughout the year encourage the growth of plants, resulting in increased production of pollen.

Tree pollens of significance include junipers arriving as early as January, ash and cottonwood in January to February (the “cotton” flying in the air in spring is not the allergen), mulberry in March, olive in April, and later privet and mesquite. Tamarisk (salt cedar) pollinates in summer, and Rhus lancia (African sumac—which has not been well studied) in the fall.

Bermuda grass and Johnson grass pollens (the latter growing in ditches by roads, and not a heavy pollen producer) are noted in April and May and continue through the summer. Canyon ragweed pollinates in spring and fall. Rabbitbush, another ragweed, pollinates in spring. With fall come more weed pollens: Russian thistle (tumbleweed), pigweed, saltbush, and lamb’s quarters.

Molds are present year round but peak outdoors in late summer and fall. Some mold spores are present after heavy summer rains, others on dry, windy days.

Because of the continued increase in pollen counts of grasses, trees, and weeds over the years, Pima County enacted an ordinance in January 1995, to control and reduce the large amounts of allergenic wind-born pollen that cause human disease. It allows for enforcement of mandatory cutting of Bermuda grass, and prohibits the sale and planting of mulberry and olive trees in Pima County. Since the ordinance was enacted, counts of Bermuda grass, mulberry, and olive tree pollens have fallen.

Spring and fall are the two major seasons for severe allergy problems. However, a person allergic to grass pollen may have symptoms almost throughout the year.

Posted in: Allergens

Allergy and the Environment