Seasonal allergic reactions are commonly caused by:
- Pollen – many plants have flowers which produce powdery pollen that is easily spread by wind. Weather can affect the amount of pollen in the air at any given time. During the late spring and early summer, grass pollen often causes allergies. Late summer and fall hay fever may be caused by weed pollen. In warmer places, pollination may be year-round. Pollen tends to travel less on rainy, cloudy or windless days.
- Molds – molds can be most anywhere, including in the soil, plants and rotting wood. Their spores float in the air like pollen and begin to increase as temperatures rise in the spring. In the US, spores reach their peak in July in warmer states and in October in the colder states. They can be found year-round in the South and on the West Coast.