Even if you've never had any symptoms of a shellfish allergy before, you can suddenly develop allergies to shellfish as an adult. In fact, 60 percent of people with shellfish allergies develop them later in life, even if they've been eating shellfish since they were young. Your chance of developing a shellfish allergy increases to 30 or 40 percent if one of your parents has a food allergy, and up to 75 percent if both of your parents are allergic. Once you have a shellfish allergy, you're most likely stuck with it for life.

If you notice symptoms of a shellfish allergy coming on in the minutes or hours after you eat shellfish, it might be a sign of allergy onset. Symptoms to look out for include hives, itching or swelling, difficulty breathing, nausea, vomiting, diarrhea or dizziness. A more dangerous symptom that requires immediate medical care is anaphylaxis. Anaphylaxis is signaled by a swollen throat that makes it difficult to breathe; a drop in blood pressure; a fast pulse; and dizziness or loss of consciousness. Anaphylactic shock is potentially fatal, so it's important to recognize the symptoms and get help right away.

Shellfish allergies are usually triggered by the consumption of one or more types of shellfish. Depending on the severity of your allergy, even traces of shellfish in your food can trigger a reaction. That's why it's important to check the labels on foods you buy to make sure there are no shellfish ingredients. At restaurants, it's a good idea to find out what's in the food you order -- even if you're not ordering shellfish outright. Occasionally, shellfish is fried in the same oil as the French fries, for instance. For some highly sensitive people, just handing shellfish or breathing in steam from cooking shellfish is enough to trigger an allergic reaction.