Do they look like someone sprinkled salt on him? That's ich. You can either try ich medication, OR raise the temperature of the tank and add some aquarium salt. Do a search on here for ich or heat/salt treatment, and you should be able to find how much salt per gallon you need to use.
Or, do they look fuzzy? That's a fungus, and you need to get a fungus medication.
If you use any medication, make sure to take the carbon out of the filter or it will filter the medication out of the water.