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Allergens: Pollen

Pollen Allergies: What You Need to Know

Dandelion blowing in the breeze
  • Pollen is the most common cause of allergic rhinitis.

  • Pollen is microscopic in size.

  • Pollen from trees, grasses and weeds is easily windblown and known to cause allergies.

What is pollen?

Pollen refers to the tiny egg-shaped male cells of flowering plants, including trees, grasses and weeds. Pollen is microscopic in size. It is the most common cause of seasonal allergic rhinitis, sometimes known as hay fever.

Which plants produce pollen that cause allergic reactions?

Plants that have powdery granules of pollen that are easily blown by the wind include:

  • Trees, such as oak, western red cedar, elm, birch, ash, hickory, poplar, sycamore, maple, cypress, walnut, catalpa, olive and pecan

  • Grasses, such as Timothy, Johnson, Bermuda, orchard, sweet vernal, red top and some blue grasses

  • Weeds, such as ragweed, sagebrush, pigweed, tumbleweed, Russian thistle and cockle weed

Most flowering plants, such as roses, have heavier, waxy pollens that are not as easily windblown.

When is pollen season?

Each plant has a pollen season. It usually starts in the spring but may begin as early as January in the southern areas of the United States. The season usually lasts until November.

More Information About Environmental Allergies from Johns Hopkins Medicine

Man sneezing

Allergies: Answers from Allergy Expert Dr. Sandra Lin

About 45 million Americans suffer from environmental allergies. Dr. Sandra Lin, a Johns Hopkins otolaryngologist (ENT) and allergy expert, answers some of the most commonly asked questions about treating environmental allergies.

Learn more.

Can allergic rhinitis in pollen season be prevented?

To lessen the effects of allergic rhinitis during pollen season, the American Academy of Allergy, Asthma & Immunology suggests the following:

  • Keep windows closed at night and use air conditioning, which cleans, cools and dries the air.

  • Minimize outdoor activities early in the morning (between 5 a.m. and 10 a.m.) when pollen is most prevalent.

  • Keep car windows closed when traveling.

  • Take a vacation to an area where pollen is not as prevalent, such as the ocean.

  • Take the medications prescribed by your doctor.

  • Don't spend much time outdoors when the pollen count is high.

  • Don't rake leaves during pollen season.

  • If you are allergic to grass, wear a mask or have someone else mow the lawn.

  • Don't hang bedding or clothing outside to dry.


For information about food allergies please visit the following pages:

More Information About Environmental Allergies in the Health Library

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