What causes your body to suddenly develop an allergic reaction to something later on in life that you weren’t allergic to before?

Question

i.e. how does ur body suddenly decide something is dangerous enough to warrant a reaction even tho it didnt cause it before

i might be using these tags wrong yeesh

In: 42

Answer 1

I remember a doctor telling me that it’s not good for children to grow up in an overly clean environment, because during those years it has something to do with the way your immune system calibrates it self