Question $20$

$0\mathrm{.}5$ pts

Tommy Lee is a $6$ y$/$o who presents with sneezing, congestion, runny nose, and itchy reddened eyes. The scratch test identifies dust mites and pet dander as the causative allergens. The doctor explains to Tommy's mother what an allergen is in layperson's terms.

An allergen is any substance that the body regards as being foreign, or an antigen. It causes the mast cells to release histamine which creates this cellular response experienced by your son.

An allergen is also an antigen that responds to a specific substance and causes a cellular level antigen$-$antibody response.

Allergies occur when your body overreacts to certain things, such as dust mites or pet dander. These substances are called allergens because they are what cause the allergic reaction that your son is experiencing.