Check this page to see some of them discussed, and to find out the true facts. Though rare, cats can contract canine heart worms. People who are allergic to cats are actually allergic to cat saliva or to cat dander. If the resident cat is bathed regularly the allergic people tolerate it better. Studies now show that the allergen in cats is related to their scent glands.
Cats have scent glands on their faces and at the base of their tails.
Entire male cats generate the most scent. If this secretion from the scent glands is the allergen, allergic people should tolerate spayed female cats the best. Cats do not think that they are little people. They think that we are big cats. This influences their behavior in many ways.