Is it possible to only be allergic to crab legs and not all shellfish?

When I was young I every so often my dad would make some shrimp and crab legs and all of that. This one particular night I was eating the crab legs, my face broke out and my lips started to itch. And we noticed that continued If I ate it again anytime after. My mom assumed I was allergic to all shellfish. But I can... show more When I was young I every so often my dad would make some shrimp and crab legs and all of that. This one particular night I was eating the crab legs, my face broke out and my lips started to itch. And we noticed that continued If I ate it again anytime after. My mom assumed I was allergic to all shellfish. But I can eat shrimp and be unaffected sometimes. Back then My lips would itch, but now that I am older I am able to eat shrimp just fine. I eat all other fish just fine, and fried clams as well. I wonder if maybe I built a tolerance for shrimp? Or I'm just allergic to crab legs alone? Is that possible?
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