Dog allergies are not to the dog itself, but to the fine dust or dander that accumulates on the dog’s skin. This dander, made up of dead skin, and saliva, can trigger violent allergic reactions. Since your child’s bed is porous, it can act like a giant sponge, trapping all those allergens, and making your child sick.
In fact, even if your child is not allergic to pet dander specifically, you should not let the dog into your child’s room. Dogs’ fur can trap any number of allergens, including pollens and other substances, which can trigger allergic reactions.
If your child has not yet tested positive for allergies, or asthma, but there’s a family history of them, you should also avoid letting the dog into your child’s room. Allergies can develop suddenly, at any time, without warning, and exposure to your dog in this way may be the catalyst.
In extreme cases of allergy to dogs, most doctors advise keeping the dog out of the house altogether, or avoiding having any pets at all.