Wax bloom is a white haze that appears on colored pencil drawings, especially when heavily worked, as a layer of the wax medium rises to the surface. It tends to appear once the work has been sitting for a week or two. To prevent wax bloom, give the drawing a couple of layers of fixative. You may need to wipe off any existing bloom first, if the drawing has taken some time to do.
More Drawing / Sketching Quick Tips
To remove wax bloom, wipe the surface gently with wad of cotton wool, checking frequently to ensure that you are not moving any pigment. A tissue also works, though can be slightly abraisive.

