When an allergy to shellfish happens it normally last a lifetime, and is most likely to appear for the first time during adulthood. A negative reaction can occur after eating seafood that has been contaminated with algae-derived neurotoxins that include ciguatera and paralytic shellfish poisoning.

Mollusks and crustaceans are the two groups that are common for shellfish allergies. They have a high instance of cross reacting between them so anyone with a shellfish allergy is advised to avoid both groups of shellfish. Shrimp is considered the worst when taking shellfish allergies into consideration.

While the allergic reactions are usually mild and limited to hives and swelling far more dangerous even life threatening symptoms can occur including trouble breathing and the person's blood pressure dropping. Hives, redness and swelling underneath the skin are the most common reactions. Swelling may occur in the lips, face, tongue, throat and other parts of the body.

Along with the swelling of the face and lips there may also be some dizziness and clouded thinking leading to a sense of fear. There are also cases where the chest tightens and vomiting and diarrhea occur. Some people will also experience a tingling sensation in their mouths. There may be an increase in the pulse rate of someone experiencing an allergic reaction to shellfish.

With more severe allergies there is a danger from the mere smell of seafood as it can set off an allergic reaction to it. There is also a connection with tropomyosin (the protein that causes the allergic reaction) and dust mites and cockroaches. A cross reaction has been know to occur in those allergic to shellfish with some insects.

There is no proof that even though some shellfish contain a lot of iodine that an allergy to shellfish will increase a risk of an iodine allergy.

Due to the commonness of shellfish allergies labeling laws are now in place for the presence of shellfish in foods in either bold type or after the ingredients are listed with the word "contains" before the type of shellfish contained in them. If you have a history of reacting to shellfish the chances are that you are allergic to them.

Not only are animals like clams, lobster and shrimp considered to be shellfish but octopus and squid are considered to be as well. Some people have allergies to certain shellfish and others have to avoid it all together.

The most life threatening reaction to shellfish is anaphylaxis of which the symptoms include an inability to breathe, dropping blood pressure, an increased pulse rate, becoming dizzy or lightheaded and even unconscious with a severe case of an anaphylactic reaction.

When one is allergic to shellfish they will have the same reaction every time they eat the shellfish.

Sources:
http://www.allergycapital.com.au/Pages/seafood.htm l
http://foodallergies.about.com/od/seafoodallergies /p/shellfish.htm
http://www.mayoclinic.com/health/shellfish-allergy /DS00987/DSECTION=2
http://www.ohiohealth.com/bodymayo.cfm?xyzpdqabc=0 &id=6&action=detail&ref=3906

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