A week ago we bought a new collar for Justin, our Labradoodle. Now his skin around the neck is clearly irritated although the collar has never been tightened too much. Can it be an allergy to the material? The new collar is made of leather and the old one was nylon.
I'd switch him to the former collar if it's possible or another nylon collar and see if there's any difference. Food or shampoo allergies can cause this too but since you didn't mention either I assume you've excluded those.