Cooler temperatures bring relief in Phoenix, but can also trigger fall allergies

As Phoenix residents finally get a reprieve from the summer heat, many will find something else to deal with: Fall allergy season is here and it may be getting stronger.

Even in the desert, Arizonans are not immune to seasonal allergies.

While springtime is the worst allergy season in Phoenix, typically peaking in March through May, some allergy sufferers will relapse in the fall. Fall pollen counts are the highest from August to mid-October.

About 30% of Americans experience seasonal allergies, and 9% of Arizonans suffer from asthma and are at a higher risk during allergy season. Yet experts say pollen has been understudied in Arizona.

Researchers are hoping to learn more about allergy triggers and how pollen-producing plants are adapting to new environmental factors. Climate change, urbanization and weather all play a role in intensifying allergy seasons across the country.

"There are other important factors that may affect pollen, not just precipitation, but humidity, wind, wind direction," said Dr. Matthew Rank, an allergist for the Mayo Clinic in Phoenix. "The amount of pollution in the air is probably influential for how much pollen is in the air. We certainly don't have it all figured out."

Different groups of plants emit pollen to reproduce at various times of the year, causing respiratory and sinus symptoms in some people. In the fall, grasses and weeds, especially ragweed, emit pollen.

Scientists say as the planet warms from climate change, causing hotter temperatures and prolonged heat into the fall, plants have a longer growing season. The first freeze typically ends pollen production, and as freezes come later and later, Americans are experiencing longer fall allergy seasons.

"A lot of vegetation emits pollen and they use the atmosphere to help move it around," said Allison Steiner, a professor of atmospheric science at the University of Michigan. "It's very climate and weather-dependent. One of the things we've been studying is how climate change is influencing when and how much pollen is being emitted."

Arizona may not be on the same trajectory because the desert vegetation depends more on water availability to grow and reproduce. But urbanization and more carbon in the atmosphere could boost pollen-producing fall weeds and grasses.

Here's what to know about allergy season and how a changing climate may affect it:

What causes seasonal allergies?

Allergy sufferers may notice symptoms with the start of a new season. Even in the desert, plants undergo a life cycle tied to changes in weather throughout the year.

"(Pollen) is how plants exchange genetic information," said Theresa Crimmins, the director of the USA National Phenology Network. "The male pollen has to get to the female flowers to fertilize them and the fruits and seeds can be grown."

Most plants rely on animals and bugs to move their genetic material, creating flowers and fruits to attract them. But a smaller number of trees, grasses, shrubs and weeds spread their genetics through the wind, creating pollen ps small enough to blow around.

These small ps can irritate the respiratory system, causing seasonal allergies. In the fall, the primary culprit of allergy symptoms is ragweed.

"A lot of people are allergic to ragweed, and ragweed usually comes out in late summer, early fall when the days start getting shorter," Steiner said.

For most people, the immune system recognizes pollen as harmless. But a smaller, unlucky percentage of people will get allergy symptoms as the body overreacts and triggers an immune response when pollen enters the nose, eyes, lungs or even settles on skin.

Seasonal allergy symptoms include a runny nose, sneezing, difficulty breathing, drowsiness from lack of quality sleep and itchy or irritated eyes. Allergies can swell the airways, putting people with asthma at a higher risk of an attack and subsequent hospitalization.

"The main problem is the body overreacts to something," Rank said. "The overreaction of the body sort of puts in play the immune system which causes some pretty unpleasant symptoms for a lot of people."

When are Arizona's allergy seasons, and how could they change?

There is only one official pollen-counting station in Arizona, run by scientists at the Mayo Clinic in Scottsdale. Dr. Sergei Ochkur, a pollen specialist at Mayo, has been collecting, counting and recording pollen samples for five years.

While researchers at the Mayo Clinic have made some observations based on the data, the counting station still lacks a long record needed to make definitive conclusions about how environmental changes impact plants and allergy seasons in Arizona.

"Arizona is different than a lot of other places as far as the distribution or the timing of pollen events," Rank said. "We found that the pollen can be discovered almost any time of year in Arizona."

Some trees in the region pollinate in January and February, causing higher pollen counts before the strongest quantities in the spring. Pollen declines during the heat of the summer, which is likely when Arizonans will feel the most relief from allergies.

"When it's above 110 degrees, plants are not pollinating," Rank said. "So in that way, it's possible that hotter temperatures and longer, warmer summers in Phoenix could potentially lead to less pollination."

When the monsoon arrives, precipitation triggers the growing season for grasses and weeds, which typically begin releasing pollen by mid-August.

"Many factors can play a role," Ochkur said. "For instance, the levels of pollution. Ozone can modify the pollen and make it more allergenic. CO2 plays a role. CO2 is a food for the plants, therefore they will grow more and produce more pollen."

Urbanization can also make allergies worse. When the land is disturbed to create roadways or housing developments, ragweed can grow back stronger. As temperatures increase, ragweed becomes more abundant.

A 2003 study found that the urban heat island effect — when concrete, buildings and other infrastructure absorb and reemit the sun's heat — can cause ragweed to grow faster and produce more pollen in cities.

Even when grass and weed pollen recedes, allergy sufferers are still at risk. Junipers will sometimes emit bursts of pollen in November and December.

"It depends on which direction the wind's blowing and a lot of other temperature conditions, which influence how much pollen we end up getting into our nose or eyes," Rank said.

As the climate, weather patterns and urbanization change the landscape, plants are likely to produce more pollen for longer, causing stronger allergy symptoms. Ochkur plans to continue collecting pollen samples to learn more about allergens in Phoenix.

How can Arizonans respond?

While seasonal allergies can be frustrating and affect quality of life for a few weeks, there are things people can do to counteract symptoms throughout the year.

Rank says there are three ways people can combat allergies.

There are also large-scale solutions to counteract allergy season. Although allergy seasons are intensifying across the U.S. due to climate change, minimizing atmospheric warming can help keep pollen under control.

"This is a side effect of climate change that could impact people's lives in ways that they might not have thought about before," Steiner said. "But ultimately, in terms of slowing the warming, that really is our best bet at trying to curb a lot of these changes in pollen."

Scientists will continue researching seasonal allergies and the plants that cause them. The Mayo Clinic hopes to observe overall trends that can inform action across the Valley, and general pollen forecasting can help people be more proactive with medication.

"We're hoping a lot of the modeling we can do can help this problem," Steiner said. "If you know that a big pollen season is coming then you can start taking medication earlier and manage your symptoms."

Hayleigh Evans writes about extreme weather and related topics for The Arizona Republic and azcentral.com . Email her with story tips at .