Interesting enough, the allergy tests he was given didn't indicate
flea allergy for him -- it was certain pollens (including a couple
of trees which is high now; some grasses which will be high in a
couple of months), mold spores, dust and dust mites, cat dander.  
Cats exhibit allergy symptoms to these mostly in their skin where
humans would get the sniffles and runny eyes.  I treated for flea
allergy for about 6 months before ruling that out even before he
was tested.  Depo Medrol used to work for him.  That's why I had to
seek another relief.  I believe in quality of life, too.  He might
have a shortened life trying to keep him comfortable.  He's
miserable without aggressive treatment.  My current vet is new for
him and I wrote her his whole history and I even wrote that at one
time I considered euthanisia because nothing would help him.  After
thousands of dollars of tests and trial treatments. I hate thinking
that, but you'd have to see him tearing his skin off when it used
to get so bad.  I had to put my foot down and demand treatment that
might be risky just to keep him comfortable. We went through the
tests. We knew what it was.