Do your dogs wear their collars all the time? If you take them off, when? I've been wondering a lot about their collars, because it seems they're obviously more comfortable without them, but at the same time I don't want them to get lost (they're microchipped but if they're found by a person that doesn't call animal control to scan them then noone will know they're mine). I keep their collars pretty loose, just loose enough so they're only tight enough that they don't fall off, but they still have been getting something on the front of their necks, where the fur feels and looks and feels thinner. I thought it was an allergy, but I checked my other dogs neck and she had the same thing, though she has a different collar of different materials.