I didn't either. Ruger has skin issues... at times his feet get so inflamed that I have to soak them twice per day. Tonight I gave him a Benedryl because I got tired of his constant scratching.
Sounds like the dog has a food allergy. As others have said, it happens in dogs more than one thinks. Most of our dogs have had food allergies even when buying the "best" commercial dog good. We spent quite a bit of time and money buying expensive dog food but they all had fillers and the dogs would react to the food.
As a result, my wife started making dog food years ago. Basically, what ever meat is cheapest, a supplement powder, along with veggies of some kind. The meat is fed raw to the dog. The difference it made to the dogs was amazing.
Quite a bit of dog food is filler, usually corn and/or rice. Corn is not really good for people and it really is not good for dogs. Wild K9's do not eat corn or rice...
Back to the OP.
I don't want anymore more dogs. We have been traveling for years and putting a dog in a kennel is expensive. While the pandemic has prevented many trips, we still are getting in some traveling.
So of course we got a rescue from the pound.

He is mostly a border collie and he has is very smart. He was in a home with a dozen other dogs and you could see his ribs. His coat looked like scat and felt rough. Poor thing had so many worms it took two deworming treatments to get rid of them all.
The wifey fed the dog her concoction and the difference was amazing. The dog put on weight, his fur turned healthy looking and smooth. He had even more energy.
He has issues. Mainly he likes to run to see other people's dogs and he barks too much. I think both of these behaviors are because he was raised in a large pack of dogs. He is friendly, though he does NOT like strangers visiting the house. He knows not to bark so much but he can't help himself. He is wicked smart he just does stupid things from time to time.
I don't want dogs at the present so we got our rescue. Then we got two more!

A family member has not one but three cancers and the person has two dogs.

It is a group family effort to care for the person and we took in the dogs almost a year ago. At this point, I think they dogs are ours. The person with cancer will not live much longer, and has lived far longer than anyone believed possible, and I think we will end up with the dogs.
I do not want any dogs so know we have three.

Later,
Dan