Severe allergy issues is an auto-immune issue. More than likely genetic.
Although I love my animals I do not veiw them as human and I think it is a fine line between keeping and medicating an animal for life and euthanizing an animal. Many years in the canine world and I more often see people's selfishness keep an animal alive, medicated and suffering. Life long meds do great damage to the animals and we are not doing them any favors.
For some though they cannot bring themselves to divide the human emotion part. I know this one well... my parents kept a dog alive with allergy issues for years... a genetic nightmare of a dog... allergic to grass, fleas, all things out doors. A dog... allergic to grass. They kept her loaded on meds that affect the liver and kidneys also the chronic misery made for a grouchy dog. One day my mom called crying, asked me to please come get the dog. I did, held her while she was euthanized. Told her how sorry I was that she had been allowed to suffer for so long.
In the end my mom was more upset as to how she had allowed the dogs suffering for so long. This was about 30 some years ago.
Many forget as we have our pets and we grow so attached and love them so much that they are animals. Dogs are scavengers by nature... meat eaters, trash eaters, whatever can be scavenged, living out on the land... meaning grass.