August is a significant month for seasonal allergy sufferers, marking a distinct shift in airborne triggers. Seasonal allergies, medically known as allergic rhinitis, are immune system reactions to generally harmless airborne substances like pollen and mold spores. The end of summer does not bring a reprieve from symptoms; instead, it ushers in a new allergy season that often lasts well into the fall. This late-summer period transitions from the grass pollens of early summer to a different set of widespread allergens that peak in August and September.
The Dominant Late Summer Allergen
The primary cause of August allergy symptoms across much of the United States is the emergence of ragweed pollen. Ragweed, a plant from the Ambrosia genus, typically begins to flower and release its pollen around mid-August and continues until the first hard frost. This weed is highly prolific, with a single plant capable of producing up to one billion pollen grains.
Ragweed pollen grains are exceptionally small and lightweight, allowing them to be carried great distances by the wind, sometimes traveling over 100 miles. Symptoms can occur even in areas where ragweed plants are not visible due to this widespread dispersal. The plant is especially prevalent in the Eastern and Midwestern states, though it grows across most of the country. Peak pollen concentrations often occur when days are warm and nights are cool, a common late summer weather pattern.
Nearly 50 million people in the U.S. experience symptoms from ragweed pollen. Other weeds, such as pigweed, Russian thistle, sagebrush, and cocklebur, also contribute to the late-summer pollen load. Exposure triggers common allergic responses like sneezing, an itchy or runny nose, and watery eyes.
The Role of Humidity and Fungal Spores
August’s characteristic warmth and high humidity create ideal conditions for mold spores. Mold is a fungus that reproduces by releasing microscopic spores into the air that can be easily inhaled. These spores thrive in moisture and are a major cause of late-summer and fall allergies.
Outdoor mold spores become particularly abundant, growing on damp, decaying matter like fallen leaves, compost piles, and mulch. The combination of heat, rain, and humidity accelerates this decomposition, leading to spikes in spore counts. Indoors, mold flourishes in basements, bathrooms, and other poorly ventilated areas where humidity levels remain high, especially above 50%. Mold spores present a constant threat both inside and outside the home, as they can spread with fog, dew, or dry, windy weather.
Practical Strategies for August Symptom Relief
Managing August allergies involves proactively reducing exposure to both weed pollen and mold spores. Keeping windows closed in the home and car is an effective avoidance strategy to prevent airborne allergens from entering. Using an air conditioner cools the air and helps filter out particles, especially when equipped with a high-efficiency particulate air (HEPA) filter.
Individuals should monitor local pollen and mold counts and plan outdoor activities when levels are lowest, often after rain or later in the day, as pollen counts peak in the morning. After spending time outdoors, immediately changing clothes and showering rinses pollen from hair and skin, preventing indoor spread. To combat mold, using a dehumidifier to keep indoor humidity below 50% is highly recommended in damp areas. Over-the-counter options, such as antihistamines and nasal corticosteroid sprays, effectively relieve symptoms when started a week or two before symptoms typically begin.