What Happens during an Allergic Reaction?
When an allergic individual is exposed to an allergen they are sensitive to, several things happen in very quick succession – in very sensitive people, the reaction is virtually immediate, and in some cases, potentially fatal if not treated quickly.
The release of IgE triggered by an allergen causes immune cells called granulocytes to release molecules that trigger an inflammatory response. This response is extremely rapid, and in some cases occurs immediately upon exposure to an allergen.
Symptoms of allergy include swelling, itching, and redness at the site of contact, and an increase in mucus secretions. Depending on the site of contact, these symptoms can be life-threatening. If they occur in the lungs, for example, these symptoms can cause breathing difficulty. Other symptoms, such as involuntary muscle contractions, nerve stimulation, and blood vessel dilation, can become serious if not treated. Severe swelling can also be fatal due to contraction of airways.
Some allergy symptoms are local (confined to one area of the body), whereas others are systemic, and occur all over the body. The nature of the allergen and the exposure to it, along with the degree of individual sensitivity to the allergen, is generally what determines whether symptoms are local or systemic. For example, asthma causes local symptoms confined to the lungs, whereas a penicillin allergy can cause systemic symptoms.