Just a crumb; nothing even as big as a morsel, OK?, but what’s this about using a ring finger for applying face treatments?
I’m not giving you medical advice, here: if your doctor or any medical person has told you to use your ring finger for applying a treatment…what I have to say should be ignored. You do what your medical professional SAYS!!!…but in the “general advice from makeup people” department…

You have to ask yourself if you really don’t trust any of your other fingers or even your THUMB, for crying out loud, to apply makeup without poking or injuring yourself.