I started a similar thread and in it we came to the conclusion that it is a myth and products containing "cain" can be used when use properly.
I never saw that old discussion from 2015 when I was mentioned. I want to clarify the story and why I've said that benzocaine can be toxic to avians. It wasn't just me, but someone else who contacted me after that happened to tell me she had a similar experience.
When my rooster died suddenly, we had put an ointment that had benzocaine, plus some aromatics like citronella, on his wattles because his hens were picking on him relentlessly. There was no warning on the box against using it on birds. He was shaking his head like it bothered him, maybe it had a sting to it, not sure. Immediately, he was fighting at the fence with a rival, breathing hard as they do, and just began to sway on his feet and dropped to the ground. He was dead within a minute.
Someone here on BYC PMd me right away with a story about show birds being banded with actual rubber bands on their feet to mark which was which prior to a show, cutting into their feet, making them bleed. She had run to the house and got a benzocaine ointment and slathered their feet with it, coming back a few minutes later to find several dead. The
veterinarian told her that it was the benzocaine in the ointment on the open wounds that killed the birds. So, it's not me who said it, but a veterinarian who examined the birds and assessed the cause of death.
Now, I can't say 100% what caused my rooster's death because I did not have a necropsy, so that is why I said I was not sure. He was only about 2 years old, but as roosters sometimes do die suddenly with heart attacks, I can't equivocally say it was the ointment or that. So, that's all I wanted to say about the story that keeps circulating. I'm not sure people remember the real reason I don't advise benzocaine pain killers for birds, especially those with open wounds. Hope this helps.