Hi Aimee,

While I don't think any real harm will come to 
your cels if you get fingerprints on them (others 
may disagree), you can leave fingerprint smudges 
visable on the cel if you handle it with your 
bare hands.  And that can detract from the look 
of the cel.  If I can see them one of my cels 
(from a previous owner), I carefully remove them 
with damp soft cloth.  

To prevent getting the smudges on there in the 
first place, I always handle my cels with a pair 
of gloves on.  You can find these where they sell 
photography supplies.

Hope this helps,
Lisa ^_^ (aka Luna-Art)