What it is
E1105 is lysozyme: a naturally-occurring antimicrobial enzyme extracted from chicken egg white. Used to control bacterial spoilage in food, particularly hard cheese.
Why it matters
Most common in Italian hard cheeses (Parmigiano Reggiano, Grana Padano, some Provolone) and some European-style fermented sausages. EU regulation requires labels to flag the egg origin as an allergen, but it's often listed only as E1105 in smaller print.
What to do
Always not vegan. Cheeses produced under strict vegan certification programmes avoid it; many traditional "cheese alternatives" contain neither lysozyme nor casein and are explicitly labelled vegan.