FRIDAY, Jan. 4, 2019 (HealthDay News) -- More than 10 percent of U.S. adults have a food allergy -- and nearly double that believe they do, a new study estimates.
Researchers found that 19 percent of those surveyed thought they had a food allergy. But when the investigators dug into people's symptoms, they found that only 10.8 percent reported "convincing" signs of a true allergy.
Experts said the findings highlight two important facts: Food allergies are common among U.S. adults, and many mistakenly believe they have one.
"There are many misconceptions around reactions to food," said lead researcher Dr. Ruchi Gupta, a professor of pediatrics at Northwestern University, in Chicago.
According to Gupta, it can be easy for people to assume food-related symptoms signal an allergy. But other conditions can be the real culprit, she said.
People with true allergies have an immune system reaction against proteins in a particular food. Those reactions, Gupta explained, can sometimes be severe -- including life-threatening breathing difficulties or drops in blood pressure.
So it's critical to get an accurate diagnosis, she noted.
Dr. Wayne Shreffler, a medical advisor to the non-profit Food Allergy Research & Education, agreed.
"Sometimes people think, 'What difference does it make? If the food makes me feel bad, I'll avoid it,'" Shreffler said.
But people with a true allergy need to completely eliminate the offending food from their diet -- and they should get professional guidance on how to do that, he suggested.
They should also get a prescription for epinephrine, Shreffler said. The drug, given by auto-injector, treats severe allergic reactions in an emergency.
On the flip side, food avoidance can be very challenging -- so people without an allergy should not do it unnecessarily, he added.
What other conditions can cause food-related woes? One possibility, Gupta said, is a food intolerance -- such as difficulty digesting lactose, a sugar in milk.
Unlike allergies, food intolerances do not involve the immune system. They arise from an issue in the digestive system -- like an enzyme deficiency -- that makes it hard to break down a particular food.
In other cases, Gupta said, people have an oral allergy syndrome. That occurs when someone with a pollen allergy has a reaction to a food with proteins similar to pollen -- usually a raw fruit or vegetable. The symptoms include itchiness in the mouth or throat, or swelling around the lips.
That type of reaction is not life-threatening, and people may be able to avert it by simply cooking the offending produce, Gupta said.
The study, published online Jan. 4 in JAMA Network Open, included more than 40,400 U.S. adults.
Overall, 19 percent reported food allergies. However, only 10.8 percent had ever suffered "convincing" symptoms -- such as hives, throat constriction, lip or tongue swelling, vomiting, difficulty breathing or rapid heartbeat.
Certain other symptoms -- like cramps or diarrhea -- were not considered convincing, because they are more likely to indicate a food intolerance.
Among people with true allergies, shellfish was the most common culprit: An estimated 3 percent of adults were allergic to shellfish. Milk allergy (1.9 percent) and peanut allergy (1.8 percent) were next in line. Many people had more than one food allergy, the findings showed.
And surprisingly, allergies often developed in adulthood, rather than childhood. Almost half of participants with convincing symptoms developed at least one of their allergies as an adult, according to the report.
It has long been known that adults can develop new food allergies. But Gupta was "really surprised" by how often that was reported in the study.
Shreffler agreed, calling the finding "striking."
It's not fully clear why food allergies arise in adults, according to Shreffler. But in some cases, he said, it may be a matter of exposure. Many kids turn their noses up at shellfish, for example -- so an allergy might not become apparent until later in life.
Gupta's team also found that only half of study participants with convincing food allergy symptoms had ever received a formal diagnosis.
Some may self-diagnose and skip the doctor visit, both Gupta and Shreffler said. But it's also possible for doctors to miss the diagnosis.
"I think that finding is a bit of a wake-up call to the medical community," Shreffler said.
Food Allergy Research & Education has more on food allergy diagnosis.
SOURCES: Ruchi Gupta, M.D., M.P.H., professor, pediatrics, Northwestern University Feinberg School of Medicine, and physician, Lurie Children's Hospital, Chicago; Wayne Shreffler, M.D., Ph.D., director, Food Allergy Center, Massachusetts General Hospital, and medical advisor, research, Food Allergy Research & Education, McLean, Va.; Jan. 4, 2019, JAMA Network Open, online