It's not really any different to letting them shove their paws in my face/mouth - which they do - or lick my hands which I then end up putting near my face. I know they've been digging around in their litter with those paws!
I just try not to think about it. It's not like I go out of my way to put their paws in my mouth, but sometimes they're just unstoppable, and like it or not in my mouth is where they end up
If I was worried about germs and dirties all the time I wouldn't be able to have such a close relationship with my cats as I do, and I like it the way it is
I draw the line at trying to get food off my plate, which Taiki does try to do, but not because he's unhygienic - more because it's naughty!