When a child has allergies, it means that his immune system reacts disproportionally to allergens like animal dander and the protein in animals' saliva. When he comes in contact with an allergen, his body sends out antibodies that tell his basophils and mast cells to release chemicals to attack the invader. Most kids who are allergic to pets are allergic to warm-blooded animals, particularly cats and dogs.
While all cats are considered allergenic, there are some dogs that have a reputation for being less allergenic than others. Still, the best way to avoid triggering allergies is to stay away from allergenic pets. Hamsters and gerbils are also not the best pets for allergic kids, since they live in a cage and step in their own urine and feces. Allergic children tend to develop an allergy to the urine and feces, so when they hold their rodent pets, they have an allergic reaction. Reptiles are less than ideal pets for children, regardless of allergic tendencies. Lizards often carry salmonella; these bacteria can lead to diarrhea and dehydration in children, and they can even be fatal in young kids. If you do end up with a pet reptile, it should be kept away from food, and your child should be told never to kiss the animal. It's also important for your child to thoroughly wash his hands after he plays with his pet reptile. An adult should be responsible for cleaning the cage. Some birds, particularly parakeets and parrots, can cause hypersensitivity pneumonitis. Also known as bird-fancier's lung, this disease can cause serious long-term damage and can even be fatal. If you have a bird in the house, you have to keep an eye on your child and watch for symptoms like shortness of breath, fatigue and slow weight gain.
The ideal pet for a child with allergies is fish. Although they're not as interactive as other animals, you might be able to interest your child in an aquarium anyway.