Tree pollen is the first type of pollen released in the spring. In the south, tree pollen can be released as early as January. In the far northern states, it is not usually found in the air until June. Tree pollen can cause an allergic reaction in some people, but only 100 or so out of the 50,000 different types of trees create pollen that causes allergy symptoms. Most pollen produced by trees does not have any effect on people.
Yellow pollen is a highly visible tree pollen. It can easily be seen on trees, and often rises in a cloud when a tree is shaken. Yellow pollen is produced by evergreen trees, primarily pine trees, including spruce, true cedar trees, fir trees, larch and hemlock. Although yellow pollen looks like it could cause an allergic reaction, in reality it does not trigger allergy symptoms at all. It can stain the skin and clothing, however.
Fruit trees produce heavy, sticky pollen that is not light enough to easily become airborne. This pollen is formulated to stick to the bodies of insects so that when they gather nectar, they will fertilize the reproductive organs inside the flower. It does not produce an allergic reaction in people.
Deciduous trees (those that loose their leaves in the fall) are the primary producers of pollen in the United States. While the makeup of each type of pollen is unique, the pollen from these hardwood trees can cause an allergic reaction in many people. Oaks are a common culprit, and so are elms, maple trees, birch trees, ash, hazel and alder trees. A person might be allergic to the pollen from just one of these trees, or to the pollen from several of them. The female version of some of these trees, include the silver maple and ash trees, do not have pollen.
Trees that produce cross-reactive pollen have pollen that is very similar to each other. If someone is allergic to the pollen from one of these trees, they will most likely be allergic to the pollen from the rest of the trees as well. Trees in this group include sequoias (redwoods), junipers, mountain cedars, and all cypress trees.
Some trees have pollens that do not fall into one of the above three categories. Poplar and willow trees produce a pollen that is very fine and does not cause allergies. Some ornamental trees do not produce any pollen at all, as they are not fruiting trees and do not need to be fertilized.