Final answer:
Someone with seafood allergies cannot eat shellfish, which include crustaceans and mollusks.
Step-by-step explanation:
Someone with seafood allergies cannot eat shellfish. Shellfish include crustaceans like shrimp, lobster, crab, and crayfish, as well as mollusks like clams, mussels, oysters, and scallops.
Allergic reactions to shellfish can range from mild symptoms like hives and itching to more severe reactions such as difficulty breathing, swelling of the face and throat, and anaphylaxis.
If you have a seafood allergy, it's important to avoid all forms of shellfish, even in trace amounts or as an ingredient in other dishes.