Seasonal Allergies

Substances you are exposed to only at certain times of the year, such as plant pollens, cause seasonal allergies.

Pollens Can Trigger Allergies

Of all the substances that can trigger an allergy, pollen is one of the most widespread. These tiny round or egg-shaped male plant cells hitch rides on air currents to fertilize other plant parts. However, not all pollen causes nasal allergies.

Allergy-causing pollens are:

• small and light enough to be carried on the wind



• produced in huge quantities



• found in areas where people live and play

In addition, the chemical makeup of the pollen determines if it will trigger an allergic reaction. For instance, pine trees produce huge amounts of pollen, making it a potentially strong allergen. But the chemical makeup of the pine pollen makes it less of an allergy trigger than other kinds of pollen. Also, because pine pollen is heavy, it tends to fall on the ground rather than drift in the air where it can reach sensitive noses.

In temperate climates such as the US, the most important sources of allergy-producing pollens are:

• trees in the spring



• grasses in late spring and summer



• weeds in late summer and fall

These plants make small, dry, light pollen granules that are perfect for riding on the wind and getting into your nose and causing allergy symptoms. Flowers, such as roses and fruit tree blossoms, rarely cause allergic reactions. Why? Because their pollens are too heavy to be carried by the wind. Instead, they are carried from plant to plant by insects, such as bees. Some people, though, who are repeatedly exposed to roses and other flowers, including florists and gardeners, can develop sensitivity to these pollens.

Tree Pollens and Allergies

Not every kind of tree produces pollen that causes nasal allergies. But enough do to make seasonal allergies from tree pollens a major health issue.

Grass Pollens and Allergies

Grass pollen is a common allergen. Yet of the more than 1,000 types of grass that grow in North America, only a few produce pollens that trigger nasal allergies.

Weed Pollen and Allergies

Weeds are the largest source of allergy-triggering pollens in North America. In late summer and early fall in North America, ragweed pollen is the number one cause of hay fever. A single ragweed plant can produce millions of grains of allergy-producing pollen.

Moving Someplace Pollen-Free To Prevent Allergies

As appealing as it may sound, it's not very likely you'll be able to do this. Airborne pollen is so light that air currents can carry it hundreds of miles from its source. For instance, ragweed pollen has been collected 400 miles out at sea and 2 miles high in the air. It doesn't matter if you live in the city or in the country. Pollen is everywhere. And it doesn't help to pull up your lawn or cut down your trees.

Some people believe they can move to the desert to escape pollen allergies, but it doesn't work. In Arizona, for instance, nonnative plants such as olive, cypress, juniper, and mulberry trees, as well as Bermuda grass, cause allergy symptoms for sensitive people.

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Written by Karen Serrano, MD
Emergency Medicine resident at the University of Wisconsin-Madison.

Reviewed by Lisa V. Suffian, MD
Instructor of Clinical Pediatrics in the Division of Allergy and Pulmonary Medicine at Saint Louis Children's Hospital, Washington University School of Medicine
Assistant Clinical Professor in the Department of Pediatrics at Cardinal Glennon Children's Hospital, Saint Louis University
Board certified in Allergy and Immunology

Last updated June 2008