system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How can I only be allergic to a specific berry and seemingly no other ones? In my case I'm only allergic to strawberries.

EDIT: I just found out that a Strawberry is not a berry. However, it is the only thing I know of that I'm allergic to. So why could someone be allergic to Strawberries and not other similar foods that are of its class.

Can someone be only allergic to apples and not other fruit?
Can someone be only allergic to carrots and not other vegetables?
gpt
You can be allergic to anything that has a unique antigen, which is just a protein tag on the surface of a cell. Your body sees an antigen that doesn't belong and sends an immune response after it. If the tag is found in multiple food items, like glutens of various forms for people with severe allergies, then you will be allergic to all of those things. If the tag is unique, then it will only be triggered by a specific food item.