Other times a pet can be kept for many years and then suddenly its owner will become severely sensitive to it. Find out from a physician what your particular allergen is, and if it turns out to be pet- related, try to reduce the allergens in the environment. Using air cleaners or filters could be a start. Your physician may also be able to prescribe medications to lessen the symptoms associated with allergies. If you are allergic to fur, a breed of dog that doesn't shed such as a Maltese might be the answer.
Dander is a common culprit in allergies to dogs.
A dog can be bathed up to twice weekly to try to alleviate the excessive dander production. Be sure though to use a medicated pet shampoo prescribed by a veterinarian and not an inexpensive alternative which can dry out your pet's skin and worsen the problem for the both of you. A non-allergic member of the family should brush the dog often, preferably outside.