"[...] For an art spray fixative, you are paying for even dispersion of the spray and a good acrylate coating that will preserve your piece.
Some hairsprays will have the same ingredients as art fixatives, but be wary of the dispersal system (spray). [...]
Also, be forewarned that many hairsprays contain hair conditioners, which is usually another name for a natural or synthetic oil. These conditioners could leave grease spots on your art. The oils to avoid are dimethicone, silicone (anyone pretty much), anything 'oil' or 'lubricant', vitamin A or E (both are oil-based), anything ending with 'glycol'. Be wary of anything listed as a plant extract.
I would think the really inexpensive, no-frills sprays might work well [...}. Just look for an acrylate in the ingredients. Suspension in alcohol is probably better than in water.
The quality of the chemical isn't any higher in art spray. The concentration might be higher, but I think extra-stiff hairspray would have at least as much. The nozzle or sprayer may be better on the art spray and the formula may have been mixed to deliver an especially fine mist."
Original text from Dr. Anne Helmenstine (About.com Chemistry Guide), you can read the full article here:
http://painting.about.com/od/pastelp...Qhairspray.htm