Seasonal Molds - The Facts

Last Editorial Review: 8/5/2002

Along with pollens from trees, grasses, and weeds, molds are an important cause of seasonal allergic rhinitis. Allergic rhinitis is the medical term for hay fever, a condition due to allergies that mimics a chronic cold. People allergic to molds may have symptoms from spring to late fall. Did you know that:

  • Unlike pollens, molds may persist after the first killing frost.
  • Some molds can grow at subfreezing temperatures, but most become dormant.
  • Snow cover lowers the outdoor mold count dramatically but does not kill molds.
  • After the spring thaw, molds thrive on the vegetation that has been killed by the winter cold.

In the warmest areas of the United States, however, molds thrive all year and can cause year-round (perennial) allergic problems. In addition, molds growing indoors can cause perennial allergic rhinitis even in the coldest climates.

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Portions of the above information was provided with the kind permission of the National Institute of Allergy and Infectious Disease. (

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