Interpretation of pollen and mold counts and their relationship to symptoms is complex. Sampling techniques such as the type of device used and its location within the community affect counts. While many patients develop symptoms when pollen counts are 20-100 grains per cubic meter, symptoms may be affected by recent exposure to other allergens, personal intensity of pollen exposure, and individual clinical sensitivity. Pollen counts reported to the public are generally taken the preceding one to three days, and may vary widely from day to day during a season. Overall, the usefulness of pollen counts in predicting symptom severity in a given individual may be limited.
Weather does have some influence on hay fever symptoms.
Days that are rainy, cloudy or windless serve to alleviate most, if not all allergic symptoms, because pollen does not move about during these conditions. The return of hot, dry and windy weather signals a return of pollen and mold distribution. Moving may help improve symptoms of allergic rhinitis depending on how different the pollens and molds in the new location are from those left behind. However, some pollens and molds, and especially grasses, are common to most plant zones in the United States and others have extensive cross-reactivity. In addition, many patients who move to a new region acquire allergies to the prevalent airborne allergens within one to two years.