sticky cards?

Some of my older decks have begun "sticking", these are decks that are rarely used. I live in a dry climate so it isn't caused by the humidity. Nothing has been spilled on them, why are they sticking? Anyone else have this happen with their older decks?

umbrae put us on to Magician's Fanning Powder. Quite inexpensive from many online magic supply sites and makes the cards slide smoothly. I have now used it on half a dozen decks that kept sticking.