My daughter is allergic to nuts so there's no way I'd take a chance on walnut shells. She had a full body hives reaction just from standing near a booth where nuts were being roasted. She was on 3 different meds for a week and it took 6 days before the hives stopped. I quit doing all swaps because of this trend of putting walnut shells in pincushions-I couldn't take the chance that I would get something that had been pinned by pins that were in walnut shells. Also, they are like wood so I can't imagine how they wouldn't dull needles.