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How do you know in advance when a day at the park or a brisk morning run is going to leave you with allergy symptoms that will stick with you for the rest of the day (if not longer)? Many people with allergies rely on reported pollen and mold spore counts to help plan their days, especially their outdoor activities, although pollen can affect your indoor air quality as well. However, you may have noticed that different sources do not always agree about the level of pollen and mold spores in the air. Once you understand how to interpret the different types of seasonal allergen data and forecasts available, pollen and mold spore counts can be an invaluable tool for managing daily allergy symptoms.

What are pollen and mold counts?

You have probably heard your local weather station talking about pollen and mold counts, especially during the spring and summer, but do you know where the data comes from? The concentration of pollen and mold spores in the air can influence the severity of allergy symptoms experienced by people with seasonal rhinitis, also known as seasonal allergies or hay fever. Pollen and mold counts establish the concentration of grains of plant pollen or mold spores in the air during a set time period, making it possible to plan to limit exposure to the airborne allergens.

To measure pollen and mold counts, researchers use air sampling equipment to collect airborne pollen and mold spores over a 24-hour period, according to the National Allergy Bureau. Then, they use a microscope to examine the sample and determine the type and concentration of pollen and mold spores present in the air. The results are extrapolated to establish the pollen count for that day.

Different organizations display pollen counts in different ways, but most use a set of classifications to interpret how much a person can expect airborne pollen and mold to affect their allergy symptoms on a given day. Additionally, some websites will break down the types of pollen and mold currently present in the air, which can be extremely helpful if you know which types of grass, trees and weeds you are most sensitive to.

How should you interpret conflicting pollen and mold counts?

Not all websites are the same, and not all pollen counting methods are the same. Pollen and mold counts may differ according to the type of sampling method used, the length of time during which the sample was collected and the analytical process, which is why some sources may report different pollen and mold counts for the same area.

The first step in interpreting pollen and mold counts across different allergen-reporting websites is to understand the different classification systems used by various organizations. For example:

  • The National Allergy Bureau (NAB) publishes a daily regional pollen and mold report that rates the level of pollen and mold spores in the air based on data collected over a 24-hour period. The report breaks down the pollen and mold counts into five different categories: absent, low, moderate, high and very high. The classifications are based on different measured concentrations of pollen and mold in the air. The NAB reports also break down pollen levels into types of trees, weeds, grass and mold.
  • provides allergy forecasts based on factors such as historical and current pollen counts, as well as weather conditions. They rate pollen levels on a scale of 0–12 and split the different ratings into five categories: low, low-medium, medium, medium-high and high, indicating the level of pollen exposure that you can expect in a given period. lists top allergens in your area along with daily forecasts.
  • The Weather Channel offers an Allergy Tracker that provides levels and forecasts for allergens based on social media reports in your area. The website classifies levels of tree pollen, grass pollen, ragweed pollen and mold spores as none, low, moderate, high, and very high. Note that the Weather Channel doesn’t explicitly disclose their source of pollen data and they merely state that pollen counts are from “local pollen reporting stations” – so to be safe, you may want to double check with other sources in determining pollen counts.

When comparing mold and pollen information from different sources, it is helpful to compare the reporting methods used by each organization. Pollen forecasts are often based on historical pollen counts for the region, as well as weather trends, and may not be the same as real-time pollen data gathered by researchers. Although real-time pollen data may be more accurate, it is often based on a 24-hour period that includes part of the previous day, so it may not reflect the most current concentrations of pollen and mold on a given day. Both types of pollen and mold reporting can be helpful to someone trying to manage seasonal allergy symptoms.

What causes high pollen and mold counts?

The reason that so many organizations are concerned with monitoring pollen and mold levels is that they can fluctuate significantly over time. Though seasonal allergens do tend to follow a cyclical pattern, there are a variety of factors that influence the amount of pollen and mold present in the air that we breathe. These can include:

  • Region and climate—As the climate varies across different regions, so too does pollen and mold growth. For example according to the American Academy of Allergy, Asthma & Immunology, colder climates may see a drop in pollen and mold production during the winter, while warmer climates can see evidence of these airborne allergens year-round. The effects of different climates on mold growth is why some regions may be better or worse places to live for people with mold allergies.
  • Season—Different types of pollen tend to be more severe during the same seasons each year. For example, tree pollen is usually more severe in the early spring, while grass pollen typically causes allergy symptoms during the late spring and early summer, and weed pollen can contribute to allergy symptoms during the late summer and early fall.
  • Weather—Pollen travels best when temperatures are high and humidity is low, meaning that pollen-related allergy symptoms tend to be less severe on cloudy and rainy days. Additionally, the windier it is outside, the easier it is for airborne pollen and mold to spread.
  • Time of day—Different plants release their pollen during different times of the day, but pollen counts typically tend to be highest in the early mornings. The NIH recommends staying indoors between 5 am and 10 am in the morning. Though lower pollen counts are generally associated with nighttime, it may depend on the type of pollen. One study (Grewling, Bogawski & Smith, 2016) found that about equal concentrations of birch pollen were found in the morning and at night. Surprisingly, concentrations of a type of ragweed pollen was found to be greater at night.

Managing your pollen and mold allergy symptoms

Pollen and mold in the air can cause allergy symptoms such as sneezing, runny nose or nasal congestion, itchy or watery eyes, throat irritation and wheezing. The symptoms that you experience will depend on the severity of your seasonal allergies and the concentration of allergens that you are exposed to on a given day. Allergies cannot be cured, but there are steps that you can take to reduce your symptoms by reducing your exposure to airborne pollen and mold.

  • Try planning outdoor activities on days when pollen and mold counts are lower. If possible, schedule time outdoors later in the day or after a heavy rain, when pollen counts tend to be lower.
  • On high pollen days, keep the windows in your home closed and use central air conditioning that can clean and dry your indoor air. If you cannot avoid going out, keep your windows closed when traveling by car.
  • Try to plan vacations and travel around high-pollen and mold seasons in certain areas, especially if you are sensitive to seasonal allergens. Research pollen and mold trends in the areas that you plan to visit and determine the best time of year to travel.
  • Avoid mowing the lawn, gardening or drying clothes outside on high pollen days.

Depending on your sensitivity to airborne pollen and mold, you may need to take precautions to reduce your exposure at different reported allergen levels than the people around you. Fortunately, many organizations simplify the process of monitoring the pollen and mold spore counts in your area, making it possible for you to plan ahead and avoid exacerbating your allergy symptoms.

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