Every summer from 1899 on, Clarence Edmonds Hemingway and his family traveled from Oak Park to Walloon Lake in upper Michigan. The retreat inspired Clarence’s son, Ernest, to write the chronicles of Nick Adams. It also gave the elder Hemingway much-needed relief-from his hay fever. A century ago, hay fever sufferers didn’t associate late summer with ragweed’s bloom, says Gregg Mitman, who is documenting the history of allergies. But, he says, “they did associate August 15th as the time their symptoms would appear quite regularly.”

Seasonal allergies, it turns out, didn’t always exist. In his new book Breathing Space (Yale University Press, $30), Mitman, a history of science prof at the University of Wisconsin–Madison, traces their rise back to the railroad expansion of the 1870s, which disturbed soils and sparked ragweed’s invasion.

While sorting through historical and medical archives, Mitman found an urban asthma epidemic from the 1960s-which largely affected Latino and African American communities-that white psychiatrists and clinical allergists at the time attributed to the emotional unrest of the civil rights movement. “That was just . . . shocking to me,” says Mitman, “that physicians and psychiatrists really considered that [as] a viable explanation [for] the first wave of the urban asthma epidemic.” In cities such as Chicago, the epidemic continues unabated to this day.