What is an antigen?

Microscopic view of a dendritic cell capturing allergen protein.

An antigen is a substance that triggers an immune reaction in your body. Antigens are typically protein-compounds like pollen, foods, dust mite, etc.

An allergen is any antigen that causes an allergic reaction such as pollen, mold, pet dander, and specific foods such as dairy, peanuts, fish, wheat, corn, and eggs, among many others.