It doesn't hurt but it's not made to last long periods of time... When it's used around the corners of your mouth it's not ideal to eat or drink or any of that either... If it's in the budget, I'd go with prosthetics... PM if you need some.
Not raggin' on collodian though, it's got it's uses and I've seen people do wonderful things with it. Id suggest stippling some adhesive on before it, do several layers to get the desired effect then stipple another layer of adhesive (preferably prosaide) or MAYBE a thin layer of latex... SOMETHING to seal it and make it last a LITTLE bit longer...
I used it a couple years ago for my Joker costume. It does feel a little like peeling off a band aid when you take it off. If you don't want to deal with that, you could use spirit gum remover for a less painless result.
Also, it took me about 7-10 layers to get the depth that I wanted. You should practice on your hand or arm first to see how many layers you prefer, and to make sure you don't have an allergic reaction.
I used it as well and if you clean your face well and make sure there is no oil or moisture when putting it on, it will actually stay on for hours. Mine did. Just swab your face lightly with rubbing alcohol beforehand. NOW...that being said I will not recommend you using it two consecutive days, nights, whatever. I used it 2 nights in a row and after the second night, I had really bad chapping along the lines from the corners of my mouth. Almost like a slight sunburn. and you guessed it, the lines were visible for a couple days! Use with care!
These are photos of the collodion before the makeup.