(CBS Newspath) – Peanut butter was Shandee Chernow’s go-to snack until she was 32-years-old. “I opened the jar of peanut butter and instantly my lungs changed, I, all of the sudden wasn’t able to breathe,” Chernow said. She became allergic to peanuts as an adult. A new study from Northwestern University Medicine shows at least 4.5 million adults suffer from peanut allergies with one in six developing a serious allergy after turning 18.

“This was actually really surprising for us that adults are developing more food allergies,” said Dr. Ruchi Gupta/Professor of Pediatrics, Northwestern University Feinberg School of Medicine. Study author Dr. Gupta says it could have to do with microorganisms that make up the microbiome of the gut as well as infections that alter the immune system and hormonal changes. “The why is the biggest question that all of us researchers across the world are asking. And we do not have a clear answer. How do we better understand this? How do we help adults with a food allergy?” Dr. Gupta said.

The study finds only 60% of adults who develop a peanut allergy are properly diagnosed and patients who develop the allergy when they’re older are also less likely to carry an EpiPen. “It’s really, really important to know what to do in case of an allergic reaction and be able to know how to manage it,” Dr. Gupta said.

Chernow wants other allergic adults to know they’re not alone. “It’s consuming and it can be really intimidating, particularly at the beginning. I would like people to know that it’s not a choice. We have to live with this. And it really is a life-threatening condition,” Chernow said.

Chernow is also allergic to tree nuts, shellfish, and pork. All allergies that came on when she was an adult. There are no FDA-approved treatments for those who develop peanut allergies as adults but Dr. Gupta says some are currently being studied.