According to the American College of Allergy, Asthma & Immunology (ACAAI), allergies rank as the sixth leading cause of persistent illness in the United States. Among the estimated 50 million Americans affected annually, a significant portion are faced with common seasonal allergies. Specifically, about 8% of adults in the U.S. contend with allergic rhinitis, commonly known as hay fever, which typically peaks during spring, summer, and early fall.
Seasonal allergies stem from the immune system’s misidentification of harmless environmental elements as harmful pathogens. This misrecognition prompts the body to release various compounds like histamines, leukotrienes, and prostaglandins, leading to typical hay fever symptoms such as sneezing, coughing, runny nose, itchy eyes, congestion, and fatigue.
However, which substances predominantly trigger hay fever? In the following discussion, we delve into the five most prevalent seasonal allergy triggers in the United States.
1. Grass Pollen
Grass pollen is lightweight and easily dispersed through the air. In the northern parts of the United States, the grass pollen allergy season typically spans from April to June. However, in the South, certain grasses may trigger allergies year-round, as noted by the American Academy of Allergy, Asthma & Immunology (AAN).
While there exist numerous varieties of grasses, only a select few provoke allergic reactions. Being allergic to one type of grass does not necessarily imply sensitivity to others.
In the northern U.S., common hay fever triggers include Timothy (Phleum pratense), Kentucky blue (Poa pratensis), rye (Lolium perenne), and fescue (Festuca arundinacea). Conversely, in the Southern region, hay fever-inducing grasses include bahia (Paspalum notatum), Bermuda (Cynodon dactylon), centipede (Eremochloa ophiuroides), Johnson (Sorghum halepense), St. Augustine (Stenotaphrum secundatum), and various species of Zoysia, as outlined by the AAN.
2. Weed Pollen
Pollen, a fine powdery substance, is generated by plants during reproduction. This microscopic grain is released into the environment by the male reproductive organs of plants, such as flower stamens and conifer male cones. Wind, insects, or other animals carry pollen to the female ovules. When airborne pollen infiltrates the nasal passages of allergic individuals, it can induce inflammation and irritation in the nose and eyes, as stated by Yale Medicine.
Late summer and early fall allergies predominantly stem from weed pollen. The Asthma and Allergy Foundation of America (AAFA) identifies various common weeds responsible for allergic reactions, including burning bush, cocklebur, lamb’s quarters, mugwort, pigweed, Russian thistle, sagebrush, and tumbleweed. However, ragweed stands out as the foremost allergen.
According to the Allergy & Asthma Network (AAN), ragweed pollen allergy ranks as a primary cause of seasonal allergic rhinitis in the United States. Ragweed plants are widespread across the nation, particularly abundant in the East and Midwest. Pollination typically occurs from early August to November, peaking in mid-September and October. A single ragweed plant can produce up to 1 billion pollen grains, capable of traveling hundreds of miles. Apart from common hay fever symptoms, ragweed exposure can lead to a blistering rash or exacerbate asthma symptoms.
3. Tree Pollen
Tree pollen marks the onset of pollen activity each year across the United States. In certain Southern states, trees may begin to produce pollen as early as January, while in the North, this typically starts around April, according to the Asthma and Allergy Foundation of America (AAFA). Pollen production from many trees continues through May, often overlapping with the grass pollen season.
According to information provided by the Allergy & Asthma Network (AAN), common tree pollen allergens include oak, maple, birch, cedar, juniper, mountain cedar (Juniperus ashei), and Eucalyptus. Particularly in regions like Texas and Oklahoma, mountain cedar triggers allergies in December, a phenomenon sometimes referred to as “Southwest cedar fever” or “Texas cedar fever.” Mountain cedar is known for its substantial pollen release, which can give the appearance of smoke in the air.
4. Mold and Fungus Spores
Mold represents a form of fungus that propagates by releasing minute spores into the atmosphere. Thriving in warm, dim, and moist conditions, mold can persist indoors throughout the year. Nonetheless, allergic reactions to fungal spores are most prevalent from July to early autumn, according to the Asthma and Allergy Foundation of America (AAFA).
Various types of mold grow on decaying logs, fallen leaves, compost heaps, as well as on grasses and grains. Mold remains viable even in cold temperatures, entering a dormant state during winter and reemerging in spring. Within indoor environments, fungi tend to proliferate in damp locales such as bathrooms, kitchens, and basements. Common mold varieties responsible for allergy symptoms include Alternaria, Aspergillus, Cladosporium, Penicillium, and mildew. Unlike food fungi such as mushrooms or yeast-containing foods, which typically do not trigger nasal, ocular, or respiratory allergy symptoms, reactions to food fungi usually stem from the direct impact on blood vessels, as noted by the AAFA.
5. Dust Mites
Dust mites, tiny arachnids belonging to the Arachnida class alongside spiders, chiggers, and ticks, are adept at hiding in various indoor environments. They can be found in carpets, upholstered furniture, bedding, clothing, soft toys, and even pet fur. Flourishing in temperatures ranging from 68 to 77 degrees Fahrenheit (20 to 25 degrees Celsius) and humidity levels of 70% to 80%, dust mites reproduce prolifically.
According to the Asthma and Allergy Foundation of America (AAFA), dust mite allergies often worsen during colder months when people spend more time indoors, within the mites’ preferred temperature range.
Dust mites primarily feed on the tiny flakes of human skin shed daily. An average adult can shed up to 0.05 ounce (1.5 grams) of skin per day, enough to sustain a population of 1 million dust mites. Both the body parts and waste products of dust mites can trigger allergy symptoms, including mild breathing difficulties, chest tightness, and eczema flare-ups, as reported by the AAFA.
To manage dust mite allergies, Harvard Health recommends environmental control measures such as regular cleaning and using allergen-resistant encasements for pillows, mattresses, and box springs. Over-the-counter allergy medications like steroid nasal sprays and antihistamines can also help alleviate symptoms. Additionally, sublingual immunotherapy (SLIT), a form of oral medication, is emerging as a treatment option for dust mite allergies.