DETROIT — Te’nika Prince knew spring had arrived when her nose started running and her eyes got puffy and her head hurt and she felt miserable.

She has been struggling with allergies her entire life.

“I would have to keep tissue with me all the time,” says Prince, 35, of Westland, Mich. “When it starts, you don’t want to do anything. You just want to lie around.”

For several years, Prince has noticed that her allergies are showing up earlier in the spring and lasting longer in the fall, a phenomenon that has been observed across the Northern U.S.

A recent study in the journal Proceedings of the National Academy of Sciences shows that there’s been an increase in the length of the ragweed allergy season, and ties the change to global warming. The study, which compared 2009 and 1995 data, has extended the official allergy season by 16 days in Minneapolis and in Fargo, N.D.

The Asthma and Allergy Foundation of America says allergy prevalence overall has been growing across all age, sex and racial groups since the early 1980s.

“We don’t know exactly why that is,” said Dr. Rana Misiak, a senior staff physician in allergy and immunology for the Henry Ford Health System. “There are a lot of theories, especially due to food allergies. Certainly, for the seasonal allergies, that does appear to be on the rise as well.”

In all, as many as 50 million Americans suffer from allergies, according to the Asthma and Allergy Foundation.