Causes:
Anaphylaxis is an acute systemic (whole body) type
of allergic reaction which occurs when a person has become sensitized to a certain
substance or allergen and is again exposed to the allergen. Some drugs, such as those used
for pain relief or for X-rays, may cause an anaphylactoid reaction on first exposure.
Histamines and other substances released into the bloodstream cause blood vessels to
dilate and tissues to swell. Anaphylaxis may be life-threatening if obstruction of the
airway occurs, if blood pressure drops, or if heart arrythmias occur.
- Can be provoked by
skin contact with poison plants, chemicals and animal scratches, as well as by insect
stings. Ingesting or inhaling substances like pollen, animal dander, molds and mildew,
dust, nuts and shellfish, may also cause allergic reaction. Medications such as penicillin
and other antibiotics are also to be taken with care, to assure an allergic reflex is not
triggered.
More from the National Institute of
Health:
Hives are
raised red welts of various size on the surface of the skin, often itchy, which come and
go. Also called uticaria, hives is usually part of an allergic reaction to drugs or food.
The term "dermatitis" describes an inflammatory response of the skin, caused by
contact with allergens or irritants, exposure to sunlight, or by poor circulation, even
stress. AVOID SCRATCHING. Scratching the rash may spread the inflammation, lead to
infection and even leave scars.
The body's immune system normally reacts
to the presence of toxins, bacteria or viruses by producing a chemical reaction to fight
these invaders. However, sometimes the immune system reacts to ordinarily benign
substances such as food or pollen, to which it has become sensitive. This overreaction can
cause symptoms from the mild (hives) to the severe (anaphylactic shock) upon subsequent
exposure to the substance. An actual food allergy, as opposed to simple intolerance due to
the lack of digesting enzymes, is indicated by the production of antibodies to the food
allergen, and by the release of histamines and other chemicals into the blood.
Allergic
reaction to bee stings occurs when a person becomes sensitized to the venom from a
previous sting. This reaction is different from the reaction to the poison in the bite of
a black widow spider, which injects a potent toxin into the blood. Ordinarily, bee venom
is not toxic and will only cause local pain and swelling. The allergic reaction comes when
the immune system is oversensitized to the venom and produces antibodies to it. Histamines
and other substances are released into the bloodstream, causing blood vessels to dilate
and tissues to swell. Severe reactions can lead to anaphylactic shock, a life-threatening
series of symptoms including swelling of the throat and difficulty breathing. Persons who
develop an allergy to bee stings should carry prescription bee sting kits to counteract
the reaction to bee venom.
A true
allergy to a medication is different than a simple adverse reaction to the drug. The
allergic reaction occurs when the immune system, having been exposed to the drug before,
creates antibodies to it. On subsequent exposure to the drug these antibodies cause
release of histamines. If severe, this reaction can result in a life-threatening situation
known as anaphylactic shock.
Alternative
names
Anaphylactic
reaction; Anaphylactic shock; Shock - anaphylactic
Definition
Anaphylaxis is a
life-threatening type of allergic reaction.
Causes,
incidence, and risk factors
Anaphylaxis is an acutesystemic (whole
body) type of allergic
reaction. It occurs when a person has become sensitized to a certain substance or
allergen (that is, the immune system has been abnormally triggered to recognize that
allergen as a threat to the body).
On the second or subsequent exposure to the
substance, an allergic reaction occurs. This reaction is sudden, severe, and involves the
whole body.
Tissues in different parts of the body
release histamine and other substances. This causes constriction of the airways, resulting
in wheezing; difficulty breathing;
and gastrointestinal symptoms such as abdominal pain,
cramps, vomiting,
and diarrhea.
Histamine causes the blood vessels to
dilate (which lowers blood
pressure) and fluid to leak from the bloodstream into the tissues (which lowers the
blood volume), resulting in shock. Fluid can
leak into the alveoli (air sacs) of the lungs, causing pulmonary edema.
Hives and angioedema (hives on
the lips, eyelids, throat, and/or tongue) often occur, and angioedema may be severe enough
to cause obstruction of the airway. Prolonged anaphylaxis can cause heart arrhythmias.
Some drugs (polymyxin, morphine, X-ray dye, and
others) may cause an anaphylactoid reaction (anaphylactic-like reaction) on the first
exposure. This is usually from a toxic or idiosyncratic reaction rather than the
"immune system" mechanism that occurs with "true" anaphylaxis, though
the symptoms, risk for complications without treatment, and therapy are the same.
Anaphylaxis can occur in response to any allergen. Common
causes include insect
bites/stings, horse serum (used in some vaccines), food allergies, and drug allergies.
Pollens and other inhaled allergens rarely cause anaphylaxis. Some people have an
anaphylactic reaction with no identifiable cause.
Anaphylaxis occurs infrequently. However,
it is life-threatening and can occur at any time. Risks include prior history of any type
of allergic reaction.
Symptoms
Symptoms may include
the following:
Note: Symptoms develop rapidly, often
within seconds or minutes.
Anaphylactic shock reaction to measles vaccine. J R Coll Gen Pract. 1987
Jan;37(294):41. No abstract available.PMID: 3668928; UI: 88035790.
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