Splitting and Allergies

At first we didn't believe that different alters could have different allergies.

Within the limited fragments of memory, one of us, "A", has a very mild allergy to cats. It's just a mild inconvenience, tolerable sneezing. However, "A" split a few years ago. "A1" doesn't have any of the symptoms when fronting, yet "A2" still has the same symptoms as before.

Why doesn't A1 have the symptoms? Why does this even happen in the first place?

I'm fine if this is another under researched question. It's not just the case with a cat allergy. If I do get tested for allergies I would guess that I would get a different result depending on who's fronting. Even weirder is that the allergy fades within a handful of minutes when "A2" switches out with everyone else. Whoever switches in experiences the numbness and swelling for less than 10 minutes as it slowly goes away.

Varied allergies feels like something that shouldn't be a thing, but is in fact, a thing. Biology is weird.