Stole the words right out of my fingers. I've been around cats and dogs since I was in the womb/little and I have allergies to both. New studies have suggested that prolonged exposure may contribute to developing allergies (e.g houses where rice is a staple are more likely to have children with rice allergies)
But, no, I don't think hair is bad for you unless you have allergies. Inhaling it wouldn't be good but it won't kill you.
Yup!
I think the doctor may have oversimplified it. If a child lives in a very clean house and is exposed to not a lot of germs, their immune system may start to think that food and other things are actually viruses or bacteria and start thinking they are, causing the child to develop a allergy.
The doctor may have been trying to say, If you don't want kids to have a compromised immune system, then let the child's immune system work, but the way they said it made it sound literal.
I've heard of people who became lost near a single foodsource, (mango's, in one instance) and survived by eating them for weeks on end, but by the time they were found, they had developed a allergy for them (and gotten sick of the taste!)
What happens is if you're over exposed to certain things, your body will stop thinking it's food/hair/etc and think something is attacking your body.