Anaphylaxis is a severe, sometimes life-threatening allergic reaction. After being exposed to a substance, sometimes even for the first time, the body releases histamine, allergen fighting antibody immunoglobulin E and other substances, which can cause airways to tighten and other symptoms.
Anaphylaxis has occurred, and been known about, basically forever. Charles Richet coined the modern term and got a Nobel Prize in Medicine in 1913 for his work.
There's a difference between a reaction, an allergy and actual anaphylaxis. Some dyes, x-rays and even aspirin can cause a reaction in people, but if it causes an anaphylactoid reaction there won't be a question. You will not casually self-diagnose an anaphylactoid reaction after watching Dr. Oz, you will know it because of airway blockage, cardiac arrest or shock. It is a full-blown medical emergency that needs professional medical attention right away and then a doctor will diagnose it. About 0.05% of the population will have have anaphylaxis to something.
While there have been reported cases of an anaphylactic reaction to exercise, it's very rare, so get off the couch. Semen and latex are also rare causes - no, your chances are not doubled if you happen to partake of both at the same time. Food and insect bites are most common causes of anaphylaxis and, among foods, peanuts top the list in western countries, while sesame is in first place in the mid-East and chickpeas are the top cause of anaphylaxis in Asia.
Shellfish is the third most common food allergy to cause anaphylaxis, which sounds like a lot, but it turns out to be rare in children, about 8 percent of cases, according to findings that will be discussed Monday at the Annual Scientific Meeting of the American College of Allergy, Asthma and Immunology in Baltimore. In a population the size of America that's 12,000 children a year, and 500 per year die from it, so take it seriously if it happens, just don't get alarmed and worry when the term shows up in mainstream media scare journalism - these people have to find new miracle foods and then things to scare us about 5 days a week so sometimes they reach a little. You're probably not allergic to gluten either, despite what a $5 billion a year marketing machine is telling people, and if you claim to have an anaphylactic reaction to GMO foods, I know how you vote. An anaphylactoid reaction to shellfish is uncommon among adults because they learned as kids they were allergic.
Why are anaphylactoid reactions from shellfish more rare in kids than people would assume? Surveys of children are unreliable but my speculation would be fewer kids eat shellfish than drink milk or try a peanut. Mine will eat batter-coated clam strips from some box my wife got at the store but not shrimp. Shellfish may just be an acquired taste for kids not living with a shrimp boat captain, and 'acquiring' less anaphylaxis may also happen. Children can outgrow anaphylaxis, even if they still have an allergy. By their late teens, 80% of kids with anaphylaxis to milk or eggs and 20% of those with anaphylaxis to peanuts outgrow it.(2)
If it can be outgrown, can it be cured? The allergic trigger can be cured. Immunotherapy against insect stings works in about 90% of adults and 98% of children but, really, if it's an anaphylactic reaction to food it is probably better just to avoid it. Immunotherapy about food will just make kids hate that food for an additional reason and if your child is one of the 500 fatalities because you thought immunotherapy would help, you're going to end up on television news being reviled.
Sunday at the conference, there is a session about exercise-induced anaphylaxis, so if you need an excuse to lay around and watch football, tell your significant other you have a condition. But don't overplay your hand and show her the program guide; it starts at 7 AM.
(1) N. Chokshi, Z. Maskatia, S. Miller, C. Davis,
Shrimp Allergy Presentation as Anaphylaxis
Is Rare in Children, 2:30 PM in Rooms 314-315 at the Baltimore Convention Center
(2) Stephen R. Boden, A. Wesley Burks, 'Anaphylaxis: a history with emphasis on food allergy', Immunological Reviews 20 Jun 2011 DOI: 10.1111/j.1600-065X.2011.01028.x