Why did I suddenly develop a food allergy?

I'm 23 and I almost died of anaphylactic shock. After 3 days in the hospital I discovered I'm suddenly allergic to shrimp and all shellfish. Why all of the sudden? I wouldn't say I've eaten an abnormal amount of seafood in my life but I never had a reaction before. Why did I suddenly develop this allergy now even though there is no family history? I have no other allergies and yet this so severe. Why?!

You definitely need this:

http://www.epipen.com/default.aspx

Insofar as shellfish, you must avoid it for the rest of your life. I don't think there is a good answer as to why people develop allergy to something. One possible answer is that your immune system may have been suppressed somewhat and over-reacted to a harmless substance. But not necessarily. In either case, it is great you survived and please take care of yourself and NEVER, EVER, EVER EAT SHELLFISH AGAIN - NEVER!!! The second time might be much worse than the first, the reaction can be stronger. And get that Epipen ASAP, carry at least two with you and have some around in places you frequent, and tell the people around you how to administer it to you should you be unable to; and always have a properly working, charged cell phone within reach and be aware of your location.

Please get the Epipens ASAP.

There is no way to know. You can develop allergies at anytime during your life, even if you were not allergic before. It is odd that you would have such a strong reaction so suddenly that you almost died but it does happen. Just thankfully your ok, so you can stay away from shellfish now. Good Luck!

I'm glad you survived such a traumatic episode of allergic reaction. I knew a bloke who was alergic to meat. Even a sausage would cause his face to blow up like a balloon and cause him to have trouble breathing. I'd love to know the reason these allergies occur intermittently throughout life; but all my research has shown that there is no definitive answer. Stay away from shellfish. By the way, I'm allergic to carrots and white grapes.

Allergies can develop suddenly or over time. Allergies are not are not inherited, but tendency towards them is. Still, it's possible to develop allergies at any age, with or without family history of them. Severity can be mild or extreme. While exposure to the substance in question is usually frequent, it may only take a few exposures for an allergy to develop.

Was there any stress on your immune system around the time this happened (i.e. viral infection)? That can play a role as well.

Food allergies are mysterious little boogers. But I should mention, be sure you talk to your doc bc it may not just be the shellfish, but the IODINE in the fish and seafood! If u are allergic to iodine you will possibly need to avoid salt with iodine in it and be sure any medical procedures are not done with iodine! Just wanted to throw that out there.