Who's asking: Sally Gawne and Kathy Miller, Jacksonville, FL
It had never occurred to me to wonder about this, but once Sally and Kathy asked the question, it seemed obvious: wouldn't a peanut allergy mean that you couldn't eat peas and beans, too?
But no, as it turns out. Most people with peanut allergies can eat most types of legumes without having to worry about allergies. The peanut allergy is a sensitivity to one or more of three chemical compounds in peanuts. Two of those compounds occur only in peanuts; one of those compounds appears in soybeans as well, so some people who are allergic to peanuts can't tolerate soybeans, either.
The bigger question is why peanut allergies are so much more common now than they used to be. No one seems to know the answer to this. One theory is that since children no longer get many of the traditional childhood diseases, they don't build up resistance to various plant substances.
My own theory is that it's natural selection at work. We see more kids with peanut allergies and asthma these days because these kids now live normal lives, instead of dying young for unknown reasons or being kept at home as invalids. They grow up and have children of their own, who also have peanut allergies and asthma. In a weird way (in my opinion), they represent the triumph of medicine over biology, not that our environment's getting more toxic.