Outdoor Allergies

Seasonal allergic rhinitis, often referred to as “hay fever,” affects more than 35 million people in the United States. These seasonal allergies are caused by substances called allergens. Airborne pollens and mold spores are outdoor allergens that commonly trigger symptoms during the spring and fall. During these times, seasonal allergic rhinitis sufferers experience increased symptoms-sneezing, congestion, a runny nose, and itchiness in the nose, roof of the mouth, throat, eyes and ears.


Pollens are the tiny, egg-shaped male cells of flowering plants.  The average pollen particle is less than the width of an average human hair.

Pollens from plants with bright flowers, such as roses, usually do not trigger allergies. On the other hand, many trees, grasses and low-growing weeds have small, light, dry pollens that are well-suited for spreading by wind currents. These are the pollens that trigger allergy symptoms.

Seasonal allergic rhinitis in the early spring is often triggered by the pollens of such trees as oak, western red cedar, elm, birch, ash, hickory, poplar, sycamore, maple, cypress and walnut. In the late spring and early summer, pollinating grasses-including timothy, bermuda, orchard, sweet vernal, red top and some blue grasses-often trigger symptoms.  Beginning in mid-August, weeds cause the majority of symptoms with ragweed and mugwort contributing the most.

Each plant has a period of pollination that does not vary greatly from year to year. However, weather conditions can affect the amount of pollen in the air at any given time. See the chart below for typical pollinating seasons.


Molds are microscopic fungi-related to mushrooms-but without stems, roots or leaves. Their spores float in the air like pollen, and are present throughout the year in many states. Unlike pollens, molds do not have a specific season, but are affected by weather conditions such as wind, rain or temperature. Outdoor mold spores begin to appear after a spring thaw and reach their peak in October.

Common airborne molds include alternaria, cladosporium and aspergillus. Molds are present in almost every possible habitat. Outdoors, they can be found in soil, vegetation and rotting wood. Molds can also be found indoors in attics, basements, bathrooms, refrigerators and other food storage areas, garbage containers, carpets and upholstery.  They may reside on Christmas trees as well.

Pollen and mold counts
At the Asthma and Allergy Affiliates, we begin counting pollens in April and continue through September.  We publish our counts on our website at: https://allergynorthshore.com/ and on our Facebook page at:

Effects of weather and location

Weather can influence hay fever symptoms. Allergy symptoms are often minimal on days that are rainy, cloudy or windless, because pollen does not move about during these conditions. Hot, dry and windy weather signals greater pollen and mold distribution and thus, increased allergy symptoms.

Appropriate treatment is the best method for coping with your allergies. Your allergist will help you determine which outdoor allergens are contributing to your symptoms. To lessen your symptoms, your allergist may also prescribe an allergy nose spray, non-sedating antihistamine, decongestant or other medications. If your symptoms continue or if you have them for many months of the year, your allergist may also recommend immunotherapy treatment, also called allergy vaccinations or shots. This treatment involves receiving injections once weekly for 3-4 months and then monthly over a period of three to five years. This treatment helps your immune system to become more and more resistant to the specific allergen, and lessens your symptoms as well as the need for future medications.


  • Keep windows closed at night to prevent pollens or molds from drifting into your home. If needed, use air conditioning, which cleans, cools, and dries the air.
  • Minimize early morning activity when pollen is usually emitted-between 5-10 a.m.
  • Keep your car windows closed when traveling.
  • Try to stay indoors when the pollen count or humidity is reported to be high, and on windy days when dust and pollen are blown about.
  • Take a vacation during the height of the pollen season to a more pollen-free area, such as the beach or sea.
  • Take medications prescribed by your allergist regularly, in the recommended dosage.
  • Don’t mow lawns or be around freshly cut grass; mowing stirs up pollens and molds.
  • Don’t rake leaves, as this also stirs up molds.
  • Don’t grow too many indoor plants if you are allergic to mold. Wet soil encourages mold growth.

This is a handout from the Asthma and Allergy Affiliates reviewing outdoor allergies including tip, tricks and typical pollinating schedules for trees, grasses and weeds in Massachusetts.  These handouts are intended for our patients and are not a substitute for discussing your (or your child’s) unique situation with one of our physicians.