Curious about Flea Bites

When I was a kid we had a dog. This was a very long time ago, long
before flea medications. The dog had a flea collar, but still had
fleas, and there were fleas in the house.

I recall my mother and my brother constantly complaining about flea
bites. I remember them showing me their ankles with red spots all
over. In the meantime, my father and I never had a single flea bite.
Since leaving home I have always had cats, and they would sometimes
have fleas, in spite of flea collars. Nevertheless, in all my life I
can't remember ever having a flea bite myself.

This has always made me curious. I have a couple questions that
someone might be able to shed some light on.

1) Is it possible for humans (or animals, for that matter) to possess
a natural flea repellent? Like maybe fleas take one whiff of me and go
"phew, stay away from that guy, he really stinks!"

2) Or maybe I'm atually being bitten, but don't display any reaction.
What I'm getting at is what is it about flea bites that makes them
itch? For example, my understanding of mosquito bites is that the
mosquito injects a blood thinner agent to help it suck up the blood;
and humans have an allergic reaction to the agent which causes the
itching and swelling. What exactly is it about flea bites that make
them itch? Is it possible for humans to be immune to this?

My cat gets Revolution and seems to have no flea problem, so it's just
my own curiosity here. Does anyone know of any scientific information
about flea bites?

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