POLLENS CAUSING ALLERGIC RHINITIS: TREE AND GRASS POLLENS
January 13th, 2011Tree Pollens
There are more than 50,000 species of trees worldwide. Some 600 to 700 of these are native to North America, but only the pollen from about 65 of these has been shown to cause allergic rhinitis. As you would expect, the trees causing symptoms are those most commonly found around and within inhabited areas.
Tree pollens generally show little cross reactivity: that is, in general, you must develop an allergy to each specific tree pollen in order for it to cause symptoms. However, there are two tree families that are exceptions: the family containing the alders, beeches, birches, and oaks, and the family of the junipers and cedars. With respect to these, if you are allergic to the pollen of one member of the family, you will probably experience symptoms from one or more other family members.
Grass Pollens
A grass is any member of the botanical family Gramineae, which contains some 4,500 species. However, the pollens of only a small percentage of the grasses – mostly members of the same subfamily – cause the majority of grass-induced allergic rhinitis. These do so because they are widely distributed and release enormous amounts of pollen into the air each season. These plants are so ubiquitous that none of us is safe from grass pollen anywhere in North America. Even in downtown New York City, you can become sufficiently exposed to grass pollen to develop allergic rhinitis.
Included in the grass family are the cereals (oats, barley, rice, corn, wheat). Most of the cereals have large, heavy pollens that can be carried on air currents only for very short distances, not the miles required of pollens that are going to cause widespread allergic reactions. Hence, grass pollen-allergic people are unlikely to be triggered by pollens from a cereal unless they are in proximity during the cereal’s pollination.
*13/322/5*