WHEN Robert Aronowitz sees friends he grew up with, he braces himself for their usual greeting. “Hey, Snot Nose. How are you doing?”

Yes, “Snot Nose” was his nickname then, and even now, his friends like to remind him of it.

“I was swept up twice a week from the streets of Brooklyn for allergy shots,” said Dr. Aronowitz, a professor of history and sociology of science at the University of Pennsylvania. Those shots, he said, “were just like orthopedic shoes — a source of middle-class Jewish pride.”

Did they help? Did he even have allergies? “Who knows?” Dr. Aronowitz said.

But that experience helps him understand the tendency today to blame allergies for tiredness, upset stomach, or any rash or illness.

Food allergies are real and can be life-threatening. It would be folly to dismiss them. But many people think they have them when they actually don’t, according to a new report commissioned by the National Institute of Allergy and Infectious Diseases. And that says a lot about how we think about food.