It’s August and the dreaded ragweed season is here. If you suffer from allergies to this pollen you are most likely very aware and probably at least a little miserable because of it. The season generally starts in August and continues until October or the first frost, however a team of environmental scientists have published findings that indicate in recent decades climate change has increased the duration of the ragweed pollen season as much as 13 to 27 days in northern latitudes ~440N. There is a strong correlation to later first frosts. This finding is consistent with the Intergovernmental Panel on Climate Change (IPCC) projections which indicate that there is increased warming as a function of latitude.

Electron micrograph of ragweed pollen. Photo Credit: CDC/ Janice Haney Carr


Ragweed, Ambrosia, is a widespread genus of the aster (Asteraceae) family. There are 21 species of ragweed in North America.  The two most problematic species are A. artemisiifolia and A. trifida. These two species are thought to cause more allergenic rhinitis and pollen asthma than all other plants together. Ragweed grows in disturbed barren soils; they are prolific on the edges of roadways, parking lots, and sidewalks.  They flourish during the heat and drought conditions which often occur in late summer when their growth and pollen formation become rampant. If these conditions continue through late summer then pollen dispersal is very high.

A longer ragweed season means not only increased symptoms for those who are already allergic and but increased sensitization for those who are not currently allergic.

This is a scanning electron micrograph of an Ambrosia trifida plant, or more commonly known as ragweed. Photo Credit: CDC/ Janice Haney Carr

Tips for avoiding as much ragweed pollen as possible from the National Institute of Environmental Health Sciences (NIEHS):

  • Avoid the outdoors between 5-10 AM. Save outside activities for late afternoon or after a heavy rain, when pollen levels are lower.
  • Keep windows in your home and car closed to lower exposure to pollen. To keep cool, use air conditioners and avoid using window and attic fans.
  • Be aware that pollen can also be transported indoors on people and pets.
  • Dry your clothes in an automatic dryer rather than hanging them outside. Otherwise pollen can collect on clothing and be carried indoors.