An allergy is the body's immune response to substances that are not inherently harmful. The immune system manufactures IgE antibodies to protect against potentially harmful entities, including bacteria and viruses. In a person with an allergy, the immune system produces antibodies that identify otherwise non-harmful materials--called allergens--as dangerous. Contact with these materials provokes the release of histamines, and these in turn trigger allergy symptoms. Approximately one-third of the population of the United States suffers from an allergy, according to the Merck Manuals. Symptoms are often merely irritating, but sometimes an allergic reaction known as anaphylaxis provokes severe symptoms than can be life-threatening.
Breathing Difficulties
A person may begin to experience anaphylaxis within a few seconds or minutes after exposure to an allergen, and possible symptoms include shortness of breath, wheezing, tightness in the throat and difficulty breathing. He may experience coughing fits or nasal congestion, and might find that his voice has suddenly become hoarse. In a February 2010 review article published in the "Journal of Allergy and Clinical Immunology," Dr. F. Estelle R. Simons noted that the respiratory tract is involved in 70 percent of the episodes of anaphylaxis. Anaphylaxis is a medical emergency, and if someone experiences a sudden onset of those symptoms, he should seek immediate medical attention.
Skin Rash
Dr. Simons notes that between 80 and 90 percent of anaphylaxis episodes involve symptoms affecting the skin. A person might suddenly develop a red, itchy rash, with raised welts--called hives. Her face and body might appear pale, or perhaps red. Health professionals at Medline Plus, a website of the National Institutes of Health, note that the symptoms of itchiness may extend to the mouth, nose and throat.
Nausea and Vomiting
Severe allergy symptoms can include a variety of stomach-related problems. The sudden onset of nausea, vomiting or diarrhea could signal anaphylaxis. Some people might experience unusual stomach pain or cramps. The American Academy of Allergy Asthma & Immunology mentions that women may feel cramping of the uterus.
Anxiety
As the other symptoms appear rapidly, a person may begin to panic. Some might experience palpitations--a sensation of feeling their heart beating, and they may feel a sense of "impending doom," notes the American Academy of Allergy Asthma & Immunology.
Dizziness and Unconsciousness
Severe allergic reactions may involve symptoms such as dizziness or light-headedness. The body's reactions might affect blood circulation, and a person may begin to turn a blue color. His pulse rate and blood pressure might drop, and he might lose consciousness or go into shock. Health professionals at the American Academy of Allergy Asthma & Immunology warn that breathing difficulties, low blood pressure and unconsciousness are the most critical symptoms of anaphylaxis, and that immediate medical attention is necessary.
