Being allergic to humans is possible but it's also rare for one human to be allergic to another human.
Most people are mostly allergic to dogs, cats, pollen, dust and other allergens.
But being allergic to humans is possible.
Not only can humans be allergic to some humans your pets or other animals can also be allergic to us humans too.
So just like you can be allergic to dogs, cats and other animals those animals can also be allergic to us humans.
It's also rare for dogs and other animals to be allergic to humans just like it's rare that humans can be allergic to humans but it does happen.