We put this collar on our anxious cat who was unfriendly & clawed a lot at night (often keeping us awake) and it worked at keeping her calm & she no longer clawed everything in our home. We could always tell when it was time to change to a new collar (approx. every 30 days) as her bad/unfriendly/irritating behavior would reappear. HOWEVER, just days after putting on her 5th collar, we noticed a large red raised oval-shaped abrasion on her neck with a surrounding balding spot near the collar. The next day, she had a gaping open wound and I removed the collar, washed the area and treated the wound. Next day it was oozing pus. Over the next week or so, it appeared to be healing: closed up very minor looking wound and her hair was re-growing...until two days ago when we noticed a swollen area below where the wound had been. Yesterday the swollen area apparently ruptured & was putrid. Today she is in surgery for a horrible absess. Our honest & wonderful vet could not absolutely verify that this wound was caused by the collar because cats also get absesses from fighting, so while we are documenting her care and plan to request reimbursement from Sergeant’s Pet Care (makers of these Sentry calming collars), the company may not decide to reimburse us for it. The thing is, our cat is 8 years old and we have never had her fight or be injured in this way. How oddly coincidental that this should happen after wearing one of these collars! Now I have been reading other reviews for the collars and cat owners have reported similar problems!