It really shouldn't be too strong as it's manufactured for ferrets plus I only gave them the dose according to their weight. I would've thought it would've caused balding on the back of the neck, as that's where I put it.
I checked them both again today and the females tail is still looking a little bare but the male's has almost all grown back!! Weird. The females skin isn't red or sore either.
I guess I just need to keep an eye on her and see if she recovers the same way as he has.
It's handy to know the spray for cats works well, I'll bare that in mind once I've used all the spot on tubes. Thanks for that!