Vanilla essence

I just wonder, I have read some advice here about putting vanilla essence on both cats to make them smell the same - is it something special about the vanilla or could I use any essence available?

I would stick with the vanilla essence as it's non-toxic and a smell cats find attractive.

I have used vanilla essence now for some time, because my cats had a huge fight (redirected aggression).
The problem just is that my cats don't like it. When I put it on them, they start to lick and scratch themselves frantically. Vilma will run away from me even if she sees the bottle. I think it has helped with the original problem.
Could they be allergic to vanilla?