You bite into an apple and suddenly your mouth starts tingling. Or you eat shrimp for dinner and get hives.
You're not a kid and you've been able to eat these foods your whole life, so what's going on?
A number of conditions could be the cause, but one is adult-onset food allergies. That's becoming allergic -- sometimes seriously so -- after reaching adulthood.
Researchers don't know for sure why some people become allergic to certain foods after adulthood, but there are several theories about triggers as well as possible remedies.
"There's so many food conditions, and it's so important to really understand what you have because you want to know how to manage it, and some of them actually have treatments," said Dr. Ruchi Gupta, director of the Center for Food Allergy and Asthma, part of Institute for Public Health and Medicine at Northwestern University Feinberg School of Medicine in Chicago.
More than 50 million Americans have food allergies, which happen when a person's immune system overreacts to something in a food, according to the American College of Allergy, Asthma and Immunology (ACAAI).
That includes about 10% of adults, according to Gupta's own research. Some allergies carried over from childhood, but nearly half of those began during adulthood. About 38% in the 2019 study of 40,000 people reported having a severe reaction to food that sent them to the emergency room.
While you can be allergic to anything, nine substances cause 90% of food allergies: peanuts, tree nuts, milk, egg, shellfish, fin fish, soy, wheat and sesame.
Among adults, shellfish allergy is the most common, affecting almost 3%, said Gupta.
Life changes a trigger
Though allergies tend to run in families, among many reasons researchers have identified for new allergies in adulthood is a change in environment. Maybe you've moved and are being exposed to different allergens, which trigger your immune system.
A viral or bacterial infection could also flip that switch.
Hormones can be a catalyst, too, especially in women. It's not uncommon to develop food allergies during puberty, pregnancy or menopause.
"Allergies are a little bit higher in adulthood in women, and we don't quite understand the mechanism yet, but it may have to do with changes in our hormones," said Dr. Tania Elliott, an ACAAI spokesperson and faculty member at NYU Langone Health in New York City.
Some women may experience worsening allergy systems during different phases of their menstrual cycles, she said.
Another possible cause: Certain medications or alcohol can change gut acidity, so the body stops breaking down certain foods the way it once did, Elliott said.
That triggers what's called an IgE-mediated immune response, which Elliott described as "a fancy term for saying that our body is reacting abnormally to something that naturally occurs in the environment."
That natural reaction triggers the body to release chemicals, including histamine, which can cause itching, redness, swelling and dilation of blood vessels, Elliott said.
Allergies can affect multiple organ systems with skin reactions, vomiting, trouble breathing and dilating blood vessels. Anaphylaxis is a severe, life-threatening allergic reaction. Your doctor may ask you to carry epinephrine so you can quickly treat this dangerous reaction.
Allergist can help with diagnosis
Food intolerance is different. The symptoms may include bloating, fatigue or other discomfort, which may show up days later instead of within minutes or hours. If you experience those symptoms, Elliott suggested keeping a food diary for about two weeks and then let a doctor analyze it. That may lead to an elimination diet to identify the culprit.
That tingly mouth some people get after biting into a fresh apple may be a condition called oral allergy syndrome.
When you're allergic to a tree pollen, for example, you may react to eating the fruit from that tree. In addition to a tingly sensation, you may get a rash or hives on your mouth. It's unlikely to cause anaphylaxis and, Gupta said, you may be able to keep eating the food.
"It's important to talk to your allergist and make sure you know what's going on," she said, because sometimes cooking the food can reduce the reaction.
That's not true, however, for those who experience a serious allergic reaction.
"Those are the ones where you need to completely avoid that allergen," Gupta said, who added that getting a formal diagnosis is important.
While 10% of adults have food allergies, about 20% of those in Gupta's study suspected they did. Many may simply have had an intolerance to a certain food -- for example, lactose in milk. About 1 in 20 in Gupta's study reported seeking a diagnosis.
A small Canadian study of 14 patients found that "adult-onset food allergy -- particularly with resultant anaphylaxis -- is an important phenomenon to recognize, even when patients have previously tolerated the food in question."
If you have a suspected allergic reaction to a food and it's not something severe enough to send you to the ER, photograph your reaction along with the food, including any spices used in the dish and share the photos with your doctor, Elliott suggested.
That's because allergies to spices are on the rise. Your doctor can do targeted testing, she said, of the specific ingredients in the suspected dish.
Just don't despair if you love crab or nuts and suddenly can't eat them. Treatments are on the way, Gupta said.
Already, there is a U.S. Food and Drug Administration-approved oral immunotherapy for peanut allergies in children. While it's not yet endorsed for adults, Gupta predicts it eventually will be.
Ongoing clinical trials are also evaluating biologic medications that alter part of the immune pathway that causes a reaction.
"I just want everyone to know, there's hope right now, in the next five to 10 years, we will have treatments for food allergies," Gupta said.
The U.S. Food and Drug Administration has more on food allergies.
SOURCES: Ruchi Gupta, MD, MPH, director, Center for Food Allergy and Asthma, Institute for Public Health and Medicine, Northwestern University Feinberg School of Medicine, and professor, Northwestern University Feinberg School of Medicine, Chicago; Tania Elliott, MD, spokesperson, American College of Allergy, Asthma and Immunology, and allergist/immunologist, NYU Langone Health, New York City