Outdoor allergies in the early spring are often triggered by the pollen of these trees:
· western red cedar
For those with outdoor allergies in the late spring or early summer, pollen from grasses such as timothy, Bermuda, orchard, sweet vernal, red top, and some blue grasses are the main cause. In late summer and fall, ragweed is the most common source of allergenic pollen but other sources include sagebrush, pigweed, tumbleweed, Russian thistle and cockleweed.
For many people, outdoor allergies tend to occur at around the same time every year because plants tend to have a very regular pollination schedule. However, recent weather history and current conditions can dramatically affect the amount of pollen that is present in the air at a given time. Latitude is another major factor in the timing of pollination. In general, pollination seasons start later the farther North you go. In the South, pollen may show up as early as January, while in the Northern U.S. it may not begin until late in April.
The other main cause of outdoor allergies is mold. Mold is a microscopic fungi related to mushrooms that tends to grow in damp places. It reproduces by producing spores, and like pollen, mold spores can travel through the air. Unlike pollen, different molds do not have specific seasons, but the level of mold spores is heavily influenced by weather conditions such as wind, rain, and temperature. Mold spores are present year round in the South and on the West Coast, but in other areas they tend to peak in July in the warmer states and October in the colder states.
Molds are present almost everywhere outdoors, including in soil, vegetation, and rotting wood. Mold can also be found indoors, especially in damp areas such as attics, basements, bathrooms, and inside refrigerators.