Anaphylaxis is a potentially life-threatening response to an allergen. When your body comes in contact with an allergen for the first time, it flags it as dangerous -- even though it's not. From then on, whenever you eat or inhale that allergen, your body kicks into gear. Your immune system releases an antibody called immunoglobulin E, which then triggers a team of chemicals to combat the invading substance. One of these chemicals is called histamine, and it's responsible for most allergic reactions. Anaphylaxis is one of these reactions.

In anaphylaxis, your blood vessels widen and cause your blood pressure to drop drastically. This also ends up effectively narrowing your airways, making breathing more difficult. Plus, the blood vessels can start to leak, thereby causing swelling. The most common symptoms of anaphylaxis are swollen eyes, lips, hands, feet and genitals, along with itching, hives, a metallic taste in your mouth and itchy, red eyes. Anaphylaxis also causes the aforementioned drop in blood pressure, a change in heart rate and sometimes dizziness or loss of consciousness. Some people describe a severe feeling of anxiety with the onset of anaphylaxis. Others experience nausea and vomiting. While inflammation of the joints is not a typical symptom of anaphylaxis, swelling (angioedema) is; the swelling isn't limited to any one part of the body.

Anaphylaxis can be caused by all sorts of allergens, the most typical of which are medications like penicillin; foods like peanuts, tree nuts, shellfish and eggs; and insect stings from bees, wasps, yellow jackets, fire ants and hornets. Since anaphylaxis normally sets in from three to 60 minutes after you come in contact with the allergen and it can be deadly, immediate medical care is required. Epinephrine injections are essential to stop the progression of the allergic response; medical teams might administer CPR, oxygen or intravenous medications to halt the attack.