Tree, grass, and weed pollens are light and powdery in composition and can be carried great distances by the wind. Fungal or mold spores are also responsible for causing allergic suffering. Fungi reproduce largely by the release of spores. The fungi are prevalent in dark, damp places like soil, and piles of rotting wood and vegetation, especially where field crops are cultivated. When the spores are dispersed, they become airborne, causing allergic reactions.
Fungal spores are present year round but can increase after rains or plowing of the fields.