Symptoms of a shellfish allergy can include hives, itching of the skin, abdominal pain, diarrhea and a tingling in the mouth, according to Mayo Clinic. For severely allergic individuals, symptoms can also include swelling of the lips, throat or face, wheezing or troubling breathing, and dizziness or fainting. Because a shellfish allergy can cause anaphylaxis, which requires immediate treatment with epinephrine, a shellfish allergy can necessitate immediate medical attention.
Signs of anaphylaxis include a swollen lump in the throat that causes airway constriction, a sudden drop in blood pressure, causing shock, and a rapid pulse, according to the Mayo Clinic. An allergy to shellfish is caused by an immune system overreaction, signaling the body to produce antibodies to the shellfish protein.
Shellfish are divided into two groups — crustaceans and mollusks. Crustaceans include crabs, lobster, crayfish, shrimp and prawns, while mollusks include squid, octopus, snails, clams and oysters. Some people with a shellfish allergy are able to eat one type of shellfish and not the other, and some people must avoid all types of shellfish. Having a family history of allergies increases the risk of developing a shellfish allergy. Shellfish allergies are most common among adults, although some children also develop the allergy, according to Mayo Clinic.