An aeroallergen is an airborne substance that causes some form of allergic reaction such as hives or itchy eyes. There are many different airborne substance that can cause allergic reactions. Pollen and spores are particularly common aeroallergens because of their prevalence in nature. An aeroallergen can affect different people in different ways; a form of pollen that has no effect on one person can cause an extremely unpleasant reaction in another. It all depends on the individual's level of sensitivity to the specific aeroallergen as allergic reactions result from hypersensitivity to a given allergen.
An allergy is a specific type of hypersensitivity in which an individual experiences an unpleasant reaction to the presence of a specific substance. Allergic reactions result from a common disorder of the immune system in which the immune system reacts violently to the presence of a harmless substance. Such a reaction generally involves inflammation that can lead to itchiness, sneezing, or runny nose. It can also aggravate existing respiratory conditions, such as asthma. While many allergens can be avoided, aeroallergens are often very difficult to avoid because many common plants and fungi release pollen and spores that provoke allergic reactions in a significant part of the human population.
Pollens are one of the most significant sources of aeroallergens as they provoke seasonal allergies in many people that are often referred to as "hay fever." The pollens that cause hay fever tend to be present during haying season, leading to the name "hay fever." An aeroallergen causing hay fever can come from many different sources, such as various types of trees, grasses, and weeds. Grass pollen, which is extremely small, is a common aeroallergen that causes allergic reactions in a significant percentage of those who suffer from hay fever. Hay fever is not caused by any specific type of pollen, so the specific nature of hay fever varies based on the pollens present in a given area and on the pollens produced in a particular season.
Spores are another common form of aeroallergen that cause allergic reactions in a significant part of the general population. Fungi release spores into the air for the purpose of reproduction. These spores tend to travel long distances through the air, giving people ample opportunities to come into contact with and to react to them. A spore's role as an aeroallergen is often particularly significant because fungi possess mechanisms that allow them to forcibly discharge their spores into the air. Undesired fungi indoors in particular can cause unpleasant allergic reactions.
