Anaphylaxis is a medical emergency which involves an acute
(affecting the entire body) allergic reaction. It occurs following exposure to an
( ), to which a person was previously sensitized.
Anaphylaxis can be caused by any . However, the most common antigens to cause such a reaction are
, , certain
s and allergen injections.
An anaphylactic reaction starts when the allergen enters the bloodstream and reacts with an
class antibody. This causes cells to release , which in turn causes the to constrict (causing difficulting in breathing), blood vessels to relax
(lowering blood pressure) and the walls of the blood vessels to leak fluid (resulting in
and swelling). The person
may also go into .
Anaphylaxis occurs immediately or at most within 2 hours of exposure to the allergen. Treatment is
an injection, which usually stops the reaction. Those who
are allergic to bee stings or certain foods should carry a dose of epinephrine with them at all times.