Always wear gloves when handling your art. It may seem facetious, but it can be very important.
Like most artists, I like to get my hands dirty and get down and dirty with my work. Often times when mounting my photographs or drawings I forget to put on my nice white gloves. This is a mistake that has begun to haunt me. Beyond the immediate smudges or mishaps there are often problems that take several months to appear.
You may have already sold the drawing or photograph, but it is bad etiquette to sell a piece of work that has not been properly cared for.
Fingerprints and smudges may appear months down the road as a result of the acid in your skin oils or chemical contamination. This is especially a concern in photography. Fix and developer can be transfered from your hands to your print very easily, the result, brown smudges will appear on your prints within a matter of months.
If you care about your work. Wear your gloves.