Elder, oak, ash, cedar, birch and holly trees all produce high levels of pollen. Airborne pollen may produce a range of symptoms, including itchy eyes, congestion and sneezing. Certain trees produce more pollen than others and a few are well known for causing problems for those who suffer from an allergy.
Pollen is a coarse powder containing the microgametophytes of trees and other seed plants. Pollen grains are too small to see with the naked eye. A tough outer coating protects each pollen grain. Air currents and certain species of insects and animals transfer pollen from tree to tree. Pollen plays an essential role in the reproductive process of many trees, and airborne pollen may trigger seasonal allergies, commonly known as hay fever.
Pollens that trigger allergies are those of anemophilous plants, which are typically produced in large quantity and rely on air currents for dispersal and transport. Spring-blooming trees, such as the oak, birch, hickory and pecan, as well as certain types of grasses, may induce pollen allergies. Antihistamines are effective for treating most pollen allergies, and decongestants are commonly used to manage symptoms. The percentage of people who suffer from pollen allergies varies between 10 and 20 percent of the population.