Last week, Reuters reported on the chronic confusion surrounding the difference between a food allergy and a food sensitivity. In fact, half of people who think they have a food allergy actually don’t. (Spoiler: It’s probably a sensitivity.) And get this: While one in five American adults has some sort of food-related condition, the majority of people don’t receive a proper diagnoses from a doctor. So, what is a food allergy and what isn’t?

You might be thinking that it’s no big deal or that people can just discover on their own which foods, if any, give them problems. Nutrition to Fit founder Lindsey Janeiro, RD, says that would be a major mistake. “Food allergies in particular are very serious and could be life-threatening,” she says. Dismissing the seriousness of a food allergy can mean a trip the emergency room, but a food sensitivity is nothing to ignore.

Before you can ace the vocabulary test, you’ll have to learn the differences. If you’re confused about how to find out if you have a food sensitivity or wonder if you may have been misdiagnosed, you’re not alone. Keep reading for all the facts.

Food allergies are not the same as food sensitivities

“A food allergy is an immune system response,” Janeiro says. The offending ingredient—whether it’s gluten, dairy, peanuts, or something else—is a dangerous invader. When you ingest a food to which you’re allergic, your body creates antibodies to protect itself from what it believes to be dangerous. “An allergic reaction is when that fight is happening,” Janeiro explains, adding that it can manifest in a wide variety of ways. Some people may break out in a rash while others may experience swollen lips. In severe cases, it can even result in cardiac failure. Whatever the reaction, it happens fast.

Food sensitivity is typically a digestive response. (Intolerance is another term used interchangeably with sensitivity.) “Generally, the symptoms are less severe than an allergic reaction,” Janeiro says, adding that this doesn’t mean they aren’t unpleasant—far from it. While a food allergy is linked to the body’s immune system, Janeiro says that food sensitivities vary. “Individuals who are lactose intolerant, for example, don’t make enough lactase, which is a digestive enzyme required to break down lactose,” she says. Some foods cause inflammation in the gut by penetrating the gut lining, which can lead to conditions like IBS or Crohn’s disease. “While many food intolerance and sensitivity reactions are located in the gut, there are exceptions,” Janeiro says. “Individuals with asthma who find themselves sensitive to sulfites may find themselves experiencing an asthma attack after consuming sulfite-containing foods from inhaling sulfur dioxide gases given off by the food or beverage as they consume it.”

Janeiro notes that celiac disease, while similar to a true food allergy because it involves the autoimmune system, is unique in that the immune system damages the villi of the small intestine after consuming even a small amount of gluten. This can lead to a variety of symptoms, such as diarrhea, heartburn, skin rashes, fatigue, and malnutrition, among others. Further, unlike an allergic reaction, the symptoms of a sensitivity might happen immediately or might occur as late as the next day, making it tricky to pinpoint the culprit.

Here’s what the testing looks like

To figure out if you have an ailment, Janeiro says it’s super important to speak with your doctor and to ask for a referral to an allergist for testing. Food allergy testing looks very different depending on the specialist and the individual, but it’s often a blood test that looks for very specific markers. (The eight most common food allergies in the U.S. are wheat, dairy, soy, eggs, shellfish, fish, tree nuts, and peanuts.) If an allergy is identified, you can consult with a dietitian, nutritionist, or health coach to work out a plan to live your best life while staying safe.

If all your blood tests came back negative, then it’s more likely you have a sensitivity. A registered dietitian or nutritionist can help you pinpoint the culprit, usually by starting you on an elimination diet and reintroducing food groups in an attempt to discover the cause of gastrointestinal distress. “This is done very slowly, ingredient by ingredient,” Janeiro says.

Unlike a food allergy test, which determines positive or negative results, Janiero explains that food sensitivities are measured on a scale. “With dairy, for example, some people can tolerate a little dairy, but not a lot.” Janeiro stresses the importance of working with a trained professional to figure out your tolerance levels in order to avoid cutting foods unnecessarily, thereby jeopardizing your overall nutrition.

How to live with a food allergy or food sensitivity

As someone who is both allergic to tree nuts and sensitive to gluten, Janeiro knows firsthand what it’s like to be diagnosed. She stresses the importance of knowing the difference for food industry and restaurant workers, but also for other people at the table. “It infuriates me when someone who simply doesn’t like a food exaggerates it to the waiter, saying they’re allergic,” she says. “If waiters think everyone is saying they’re allergic when they simply don’t like something, they’re less likely to take it seriously.”

Janeiro’s food allergy is so serious that even tiny remnants of nuts could put her life in danger. But that doesn’t stop her from eating at restaurants. “You have to communicate very clearly to the waiter how serious it is,” she says, adding that this is not a time to worry about what people think. “I’ve been at restaurants where they’ll make my salad and forget to leave out the nuts. I’ll see someone in the kitchen pick them out before giving it to the waiter to hand to me. And I’ve asked for them to make me a whole new salad.”

If you have a food sensitivity, you should be similarly straightforward. Why live with uncomfortable digestive problems because you’re nervous about what the waiter might think? You can be both nice and up-front, but if they get it wrong, you shouldn’t be afraid to ask them to make it right.

As with almost everything else in life, when it comes to food, knowledge is key. Once you’ve done your detective work and have a proper diagnosis, you can take active steps toward avoiding what’s setting you off—and subbing in ingredients that are just as delicious.

If you’re wondering if it’s possible to outgrow a food allergy, here’s the verdict. And here’s the answer to whether or not you can develop a new allergy later in life.