Pet allergy development? Why develope pet allergies later in life?

An allergist revealed I'm allergic to dogs and cats, but nothing else. My allergy developed about a decade ago in my mid-teens, I had been having dogs and cats since my infancy.

What caused me to be allergic? Is it the long term exposure from years of having pets? Funny thing is I'm not allergic to anything other than dogs and cats, the two things I had for the longest.

Allergies are a funny thing people develope allergies and also grow out of allergies. I've always been allergic to cats and that has never changed but earlier as a child I was very allergic to dogs, I had allergy shots and eventually grew out of dog allergies in my teens. I'm still mildly allergic, if I roll around with my dog and wrestle with him I'll break out in hives but daily activities just walking him, petting him, laying on the couch with him don't really bother me. It's argued whether this is true or not but many believe you can develope an immunity to your pets proteins in their saliva or dander but other people's dogs will bother you.

Also, it's not really strange your only allergic to dogs or cats. Many people are only allergic to mold, polin or dogs or cats. I would doubt having an animal would grow your allergy.