From salmon to scallops, many people love seafood. But unfortunately for some seafood lovers, there’s a chance of developing an allergy to shellfish and fish. Even though they both fall into the category of "seafood," fish and shellfish are biologically different, so fish will not cause an allergic reaction in someone with a shellfish allergy, or vice versa.

A seafood allergy, like every allergy, is when your immune system identifies something you come in contact with as harmful. When you have an allergy, and eat fish or shellfish, your immune system releases histamines, which then cause your allergic symptoms.

Fish and shellfish allergies are uncommon but serious: an allergy to seafood can result in anaphylaxis—a life-threatening allergic reaction. Many people who develop a seafood allergy do so as an adult, 60% of shellfish allergies and 40% of fish allergies began in adulthood, and their reactions can be severe. These allergies can be caused by seafood that you’ve eaten before with no issues, but once you develop a seafood allergy, you’ll usually have this allergy for the rest of your life.