It's Springtime...What's in the Air?
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
Seasonal allergic rhinitis and asthma are caused by pollen allergens from trees, grasses, and weeds. Springtime brings an abundance of tree and grass pollens, which are typically small and light, enabling them to be windborne for long periods. These characteristics also give them easy access to the upper and lower respiratory tracts. Repeated exposure to pollen in sensitive individuals increases the likelihood of an allergic reaction. The result: itchy, watery eyes, stuffy sneezy itchy drippy nose, and even asthma.
Pollen counts measure the amount of each pollen species and are represented as the number of pollen grains per cubic meter of air (grain/m3). The counts are affected by local weather conditions: lower on rainy days and higher on hot humid days. Pollen counts are also highest in the morning and evening hours. Most pollen sensitive individuals start having symptoms when pollen counts are greater that 50-grain/ m3. Generally, in North America, tree pollens peak in April and May, while grass pollens are highest from May through August. Weed pollens predominate in the fall months. In areas such as Southern California, seasons are longer and less well delineated than in other areas such as in New England or the South Eastern United States.
Pollen from deciduous trees (e.g. Birch, Elm, Oak, Alder, Olive) is more allergenic than that from conifers (e.g. Cedars and Cypress). Although pine pollen is abundant, it is heavier, falls to the ground quicker, and is therefore less likely to enter the respiratory tract or eye membranes. Pollen from fruit trees is usually not allergenic.