Achoo! Sniffle, Sniffle! Scratch, Scratch, Scratch!

What are Seasonal Allergies? Why Do We Get Them?

With the advent of spring comes the welcoming of warmer temperatures, longer daylight hours, and the desire of many, especially outdoor enthusiasts, including gardeners, to breathe in the fresh air and dig in the dirt. Unfortunately for some, these pleasures can be accompanied by the onset of seasonal allergies, an exaggerated response of the body's immune system to an otherwise inert environmental substance, an allergen. Allergic reactions can occur through contact at or below the skin surface, as well as oral or respiratory exposure.

The onset of sneezing, sniffling, and itching share common biological pathways. The first time the immune cells encounter an allergen, a specific type of antibody is produced and released. These antibodies then bind to a different immune cell, the mast cell, setting the stage for its activation. Upon subsequent exposure to the allergen, the mast cell releases inflammatory chemicals, including histamine. Histamine interacts with capillaries, causing fluid from the blood to enter the surrounding tissue, resulting in swelling, redness, and inflammation. Additionally, constriction in the respiratory tract, as well as sensory nerve stimulation and itching, can occur. These responses typically occur a few minutes after exposure.

A sneeze or sniffle begins with an encounter with a foreign particle or allergen inside the nose. This, in turn, stimulates histamine release and mucus production. Sneezing results from local nerve cells signaling the brain to contract muscles in the mouth and respiratory tract and force the expulsion of droplets that can travel up to 24 feet. Sniffles are characterized by mucus production in the nose and eyes, causing congestion, a runny nose, and tearing.

The vicious itch-scratch cycle can be a challenge to break and can lead to the development of a rash. Allergen-skin contact initiates inflammation. Local nerve cells signal the brain to stimulate the urge to scratch. Scratching damages the skin, allowing other foreign substances to enter, exacerbating the cycle of inflammation, itching, and scratching.

While both the common cold and allergies share common symptoms, including a runny and stuffy nose, sneezing, and coughing, a cold may be accompanied by fever and chills. Allergies alone produce watery and itchy eyes. Cold symptoms typically resolve in 1 to 2 weeks, while allergies can resolve quickly or last much longer, depending on exposure to the allergen.

Pollen and Other Allergens

The release of pollen, the male sex cell and plant allergen, corresponds with optimal plant reproduction. It can range in size from the smallest, forget-me-not (Myosotis spp.), at 0.005 mm in diameter, to the largest, aquatic eelgrass (Zostera), measuring 2.5 mm long. The geometric shape optimizes dispersal methods, either by wind, water, insect, or animal. Data from 2022-2024 collected by the National Allergy Bureau and the American Academy of Allergy, Asthma and Immunology indicates an earlier start to pollen season, as well as higher pollen counts both nationally and throughout our region. 2024 was the warmest year on record for Pittsburgh, mirroring global temperature increases. Additionally, fluctuation in the amount and timing of precipitation strongly correlates with pollen counts.

Common allergens peak at different seasons. Tree pollen, typically seen coating cars and other outdoor surfaces, is highest in the spring. Summer sees a rise in grass pollen, followed by weeds in the fall. While falling winter temperatures may limit outdoor time, it tends to increase exposure to indoor allergens, including mold spores. The relative amount of allergens produced per organism varies. Mold creates the most, followed by trees, weeds, and grasses. However, the allergic potency of each depends on multiple variables, including climate, geography, presence of reactive chemicals in the allergen, and size.

Some trees commonly found in southwestern Pennsylvania that are the known culprits of spring allergies include pine (Pinus spp.), birch (Betula spp.), oak (Quercus spp.), maple (Acer spp.), elm (Ulmus spp.), cedar (Cedrus spp.), walnut (Juglans spp.), sycamore (Platanus spp.), and hickory (Carya spp.). Tree pollen production typically runs from mid-to-late winter through early spring, peaking towards the end of this period. Millions of pollen grains can be produced by each pinecone or catkin. Dispersal is airborne. While most grains are spherical, pine pollen is composed of a central body flanked by two air sacks that facilitate long-distance travel.

Many grass species in our region contribute to summer allergies, including Kentucky bluegrass (Poa pratensis), fescue (Festuca spp.), Bermuda grass (Cynodon dactylon), perennial ryegrass (Lolium perenne), and Timothy grass (Phleum pratense). While these include rhizomatous and bunch-type species, all typically produce spherical pollen grains from the inflorescence. Pollen levels increase from May through August, peaking in June. Grass pollen is mainly dispersed by the wind.

Ragweed (Ambrosia artemisiifolia) pollen is considered a principal fall allergen. It peaks from August through mid-September. Each plant can produce a billion pollen grains, which can remain airborne for days and travel hundreds of miles.

Mold, a member of the fungi kingdom, releases spores from the fruiting body situated atop a stalk, which emanates from the underground root-like mycelium. The spherical spores are both indoor and outdoor allergens, peaking during the rainy spring and fall seasons.

The rash from poison ivy (Toxicodendron radicans) is caused by contact with urushiol, an oily resin present in all parts of the plant. Allergic sensitization requires a series of cellular events beginning with initial contact, followed by the generation of long-lived immune cells. These cells recruit additional immune cells, which result in an inflammatory lesion – small blisters and a red rash. This response occurs 1 to 3 days after exposure and is limited to the actual site of plant-skin contact.

Strategies to Deal with Seasonal Allergies

Proactive, commonsense interventions may help reduce seasonal allergy symptoms. Reduce pollen exposure by limiting outdoor activities when pollen counts are high. Cover your head, eyes, nose, and mouth while outside. Wear long sleeves and pants when working in overgrown and weedy areas. Shower and change clothes after being outdoors. Keep windows closed and use HEPA filters to decrease indoor airborne allergens. Consult your doctor about additional medical treatment options.