Now, let's discuss the mechanism by which an allergic reaction takes place and let's focus on some of the or one of the most common types of allergic reactions known as hay fever. Hay fever is not an actual fever in the sense that it doesn't actually increase the core temperature. Instead, hay fever is simply the name for the allergic reaction that takes place when grass pollen actually enters the air passageways of our lungs. So one very common allergic reaction is hay fever, which is the way our immune system actually responds to grass pollen. When the allergic individual inhales pollen, that pollen, which is essentially a microscopic particle, can begin to release antigens that our body sees as pathogenic. So let's take a look at the following diagram to illustrate how our mechanism is actually carried out.