n many areas of the United States, seasonal allergies begin in February and last until the early summer. Tree pollination begins earliest in the year followed by grass pollination later in the spring and summer and ragweed in the late summer and fall. In tropical climates, however, grass may pollinate throughout a good portion of the year. Mild winter temperatures can cause plants to pollinate early. A rainy spring can also promote rapid plant growth and lead to an increase in mold, causing symptoms to last well into the fall.
The most common culprit for fall allergies is ragweed, a plant that grows wild almost everywhere, but especially on the East Coast and in the Midwest. Ragweed blooms and releases pollen from August to November. In many areas of the country, ragweed pollen levels are highest in early to mid-September.
Other plants that trigger fall allergies include:
- Burning bush
- Sagebrush and mugwort
- Tumbleweed and Russian thistle
The immune systems of people who are allergic to mold spores or pollen treat these particles (called allergens) as invaders and release chemicals, including histamine, into the bloodstream to defend against them. It’s the release of these chemicals that causes seasonal allergies symptoms.