A pet allergy is your immune system's overreaction to an animal's saliva, urine or dander. When your body comes in contact with or breathes in one of these harmless allergens, it sends out antibodies to fight them off. The antibodies instruct your basophils and mast cells to release chemicals that can eliminate the aggravating allergen. However, these chemicals -- particularly histamine -- also cause allergic symptoms like itchy eyes, runny nose, sneezing and coughing. If you notice that your child has any of these cold-like symptoms, or if he has a rash or red spots where he's come in contact with a pet, he may have a pet allergy. Pay attention to whether the symptoms go away after a week or two (as they would with a cold) or whether they persist all year round.

Pet allergies normally develop by the time a child turns 10, and since allergies are hereditary, if you or your partner has any type of allergy, there's a good chance your child has one, too. But since a number of allergies can cause the same or similar reactions, just because you spot the symptoms of a pet allergy in your child doesn't necessarily mean he has one. A trip to the doctor may be able to ascertain if your child is allergic to your pet, or if his allergy is being caused by a different environmental factor, like dust mites or mold.

Allergists can do a skin test in which drops of various allergens are pricked or injected into your child's skin. If a red bump develops on the site of a prick, it indicates a specific allergy. The tests can be performed on infants, but they're considered most reliable on children who are over two years old. Keep in mind that just because a child reacts positively to an allergen on the skin test doesn't mean he's allergic; he also needs to display symptoms of the allergy on a regular basis in order to be positively diagnosed.