Remember that many pets will outgrow their original housing or bedding, and need larger quarters. Many people find they are allergic to specific types of animal dander. Cat allergy is most common, but the problem can also exist with dogs, rabbits, rats, mice, hamsters, guinea pigs, etc. Bedding or other cage materials can sometimes trigger allergic reactions. Birds can carry allergy-provoking mites, molds or pollen on their feathers.
Some people are allergic to molds that can grow in fish tanks, or to the fish food itself.
Even reptiles can cause allergic reactions in certain individuals. Try to spend a few hours with your future pet, to see if you get a reaction. If allergies or asthma are already a serious problem, consult your doctor before you make a decision about getting a pet. Different pets require different amounts of care. Active dogs, for instance, require training, plenty of walks, daily exercise, and play sessions.