I thought allergies are built up over time and so vary greatly with individuals, a perfect sample of the "nurture" side of the coin. (Though I'm sure you can have genetic predispositions.)

Here is one thing that came up after googling: https://www.nytimes.com/2003/11/25/science/q-a-twins-and-all...

> In other studies, asthma, which is often tied to allergies, showed up in both identical twins only 20 percent of the time.