A hypersensitive state that results from exposure to an allergen defines allergy. Allergic reactions range in clinical manifestation from an immediate life-threatening condition seen within seconds of an exposure to delayed type reactions, the manifestations of which may not be seen until hours or days after the exposure.

 
Immediate or anaphylactic reactions that occur in the dental office pose the greatest risk to patients and are those that concern dentists the most. Anaphylactic reactions usually result from drug administration or reaction to an allergen in impression material or other materials used in the oral cavity. The most frequent cause is related to drug administration.
 
Generalized anaphylaxis is the most life-threatening situation occurring in a dental office. Signs and symptoms of anaphylaxis vary; however, they generally affect the skin, smooth muscle, and respiratory and cardiovascular systems. Anaphylactic shock is the term used when consciousness is lost as a result of hypotension from an anaphylactic reaction. Symptoms usually spread beginning with the skin, followed by the eyes, nose, and gastrointestinal system and then the respiratory system; finally, cardiovascular symptoms develop.
 

Prompt therapy can stop the reaction. Epinephrine is the drug of choice in an immediate reaction because the onset of action is almost immediate. Administration of corticosteroids is to prevent relapse; the onset of action of steroids is 6 hours. 
 
If epinephrine and antihistamine administration do not reverse obstruction of the airway, intubation or cricothyrotomy may be necessary.