It's estimated that around 8 percent of babies are born allergic to dogs but if a baby is exposed to dogs then they may not develop allergies to dogs later on in life.
That is if the baby isn't already allergic to dogs when they're born.
It's also estimated that 70 to 75 percent of people have dogs or cats in their house so most babies are not allergic to dogs or even cats.
If a baby is allergic to dogs or cats though then having a dog or cat in the house is not a good idea and you should find a new home for the dog or cat.