Severe systemic allergic reaction is generally caused by substances that include some foods, medications, insect stings and latex. Anaphylaxis is a very severe allergic reaction that occurs within minutes of exposure to an allergen. It is a medical emergency and if not treated in time, can lead to anaphylactic shock and even death. Symptoms can include a feeling of warmth, flushing, tingling in the mouth, red itchy rash, feeling of light–headedness, shortness of breath, severe sneezing, anxiety, stomach or uterine cramps, and/or vomiting and diarrhea.Without immediate treatment and expert care, anaphylaxis can be fatal. Mechanism of anaphylaxis Anaphylactic reaction occurs when a person has become sensitized (that is, the immune system has been triggered to recognize a substance 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. The immune system releases antibodies. The tissues release histamine and other substances. This causes muscle contractions and constriction of the airways, resulting in wheezing, difficult 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 so on.) often occur, and angioedema may be severe enough to cause obstruction of the airway. Responsible allergens for anaphylactic reaction Anaphylaxis can occur in response to any allergen. Common causes include insect bites/stings, horse serum (used in some vaccines), certain drugs and food. Pollens and other inhaled allergens rarely cause anaphylaxis. The exact cause in some anaphylactic reactions cannot be prevented. Can it be prevented? The risk of anaphylactic reaction is greater in patients with the prior history of any allergic reaction. It is very important that patients should provide information to the health care provider so that effective and prompt help can be provided.