[General] ‘have an allergy to’ VS ‘be allergic to’

[northpath]

An American acquaintance of mine said that the sentence
Sorry, I have an allergy to cats.
sounds too formal and should be replaced with
Sorry, I am allergic to cats.
Is she right?

 

[emsr2d2]

I'm not sure it's a question of formality but the second version is certainly more natural and common in BrE.