There are products on the market that are designed to clean skins. These products will remove sticky substances, for example klister that came from the track.

If there is dirt or a non-sticky substance on the skin, isopropyl alcohol will work very well.  Isopropyl alcohol is inexpensive, easily accessible and nontoxic.  We use it to clean the bases of skis after they have been stone ground and before we start the waxing process.

Regardless of which product you use to clean the skins, use as little of the liquid as possible and use a light touch with the cleaning cloth. It is best if the liquid does not get down to the base of the skin so as not to effect the integrity of the glue.