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What is pollen?

Pollen is a fine powdery substance composed of microscopic cells that come from flowering plants, including trees, grasses, and weeds. It’s the most common cause of “hay fever,” also known as seasonal allergic rhinitis.

Plants that produce pollen include:

  • Oak, western red cedar, elm, birch, ash, hickory, poplar, sycamore, maple, cypress, walnut, and other trees
  • Grasses such as Bermuda, timothy, orchard, sweet vernal, red top, and some blue grasses
  • Weeds like ragweed, sagebrush, pigweed, tumbleweed, cockleweed, and Russian thistle.
  • Most flowering plants, such as roses, have heavier, waxy pollens that do not trigger allergies.

When is pollen season?

Every plant has its own pollen season, but in general pollen season lasts from the early spring until October.

Are there ways to prevent or minimize hay fever during pollen season?

  • Keep windows closed at night and use air conditioning, which cleans, cools, and dries the air.
  • Minimize your child’s outdoor activities between 5 and 10 a.m., when pollen is most prevalent.
  • Drive with the car windows closed.
  • When the pollen count is high, minimize the amount of time your child spends outdoors.
  • Do not permit your child to play in piles of raked leaves.
  • Do not hang your child’s bedding or clothing outside to dry.
  • Give your child the medications prescribed by your child’s physician.
  • Vacation in areas like the seaside, where pollen is less prevalent.

Practitioners Who Specialize In This Condition

Brittany Esty, MD, MPH

Brittany Esty, MD, MPH

Director of Quality Improvement and Patient Safety, Division of Immunology; Immunologist, Division of Immunology
Assistant Professor of Pediatrics, Harvard Medical School
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