Consider checking closely for snake mites or other external parasites as they are often correlated with a dusty white snake.
Does the skin look intact? (as opposed to abrasions, ulcers, cuts, sores ect)
How does the rest of your snake look? Dehydrated, skin folds, losing weight, still eating, acting normal?
If no other symptoms I would begin with reassessing the husbandry. Consider what temps you have, the humidity, substrate, and perhaps note anything that may have brought in fungus or parasites.
If no improvement after any changes you've made, or the next shed, then I would proceed to your vet clinic and see what advice he has after a proper exam.
Good luck 