Food allergies occur when the immune system overreacts to proteins in certain foods, triggering symptoms that range from mild hives to life-threatening anaphylaxis. This guide covers the most common food allergens, how to recognize symptoms in adults and children, what to expect from allergy testing, and how to tell the difference between a true allergy and a food intolerance.
Most Common Food Allergens
While technically any food can trigger an allergic reaction, nine foods are responsible for about 90% of all food allergies in the United States:
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Milk: One of the most frequent allergies in babies and young children, though many outgrow it.
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Eggs: Often appears in childhood and may resolve by the teenage years.
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Peanuts: A legume (not a tree nut) that tends to cause more severe reactions.
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Tree nuts: Almonds, walnuts, cashews, pecans, and pistachios fall into this category.
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Wheat: Distinct from celiac disease, which involves a different immune response.
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Soy: Commonly hidden in processed foods under various names.
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Fish: Salmon, tuna, cod, and halibut are frequent culprits.
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Shellfish: Shrimp, crab, lobster, and scallops; this allergy often develops in adulthood.
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Sesame: Added to U.S. labeling requirements in 2023 due to rising allergy rates.
Many allergens can appear in packaged foods under unexpected names or as hidden ingredients. If you have a confirmed food allergy, you should read food labels carefully every time you are consuming packaged foods. It’s also important to communicate your food restrictions with anyone handling your food (restaurants, schools, and caregivers) to avoid accidental exposure and stay safe.
What Causes Food Allergies?
Your immune system is designed to protect you from genuine threats like bacteria and viruses. In people with food allergies, the antibodies in the immune system mistake proteins in certain food for threats. When you eat a trigger food, antibodies signal your immune system to release histamine and other chemicals, and this chemical cascade produces the symptoms we associate with allergic reactions. The whole process can unfold within minutes, which is why food allergies can feel so sudden and alarming.
Symptoms of a Food Allergy
Food allergy symptoms vary widely from person to person. Some people experience mild discomfort, while others face life-threatening emergencies. Reactions typically begin within minutes to two hours after eating the problem food, though delayed reactions do occasionally occur.
The most common symptoms include:
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Hives, itching, or eczema flare-ups
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Swelling of the lips, tongue, throat, or face
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Tingling or itching sensation in the mouth
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Stomach pain, nausea, vomiting, or diarrhea
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Nasal congestion, sneezing, or difficulty breathing
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Dizziness, lightheadedness, or feeling faint
Anaphylaxis
Anaphylaxis represents the most severe form of allergic reaction. During anaphylaxis, the throat can swell shut, blood pressure drops dangerously low, and the heart races. Without immediate treatment with epinephrine, anaphylaxis can be fatal.
If you or someone nearby shows signs of anaphylaxis after eating, use an epinephrine injector if available, and call 911 immediately. Even if symptoms improve after using the epinephrine injector, you or the person affected must still go to the hospital for observation in case a second wave of symptoms occurs.
How Long Does a Food Allergy Reaction Last?
The duration of a food allergy reaction depends on how severe the allergy is, how much of the food was eaten, and how quickly treatment begins. Mild reactions like hives or an upset stomach often clear up within a few hours, especially if you take an antihistamine. More intense reactions can linger longer.
Anaphylaxis can come in two waves. This is called a biphasic reaction. Symptoms improve at first, then return several hours later without any additional exposure to the allergen. This unpredictable pattern is one reason why doctors often recommend staying under medical observation for at least four hours after a serious reaction. If you've ever had a significant allergic reaction to food, carrying two epinephrine auto-injectors is also a good idea and provides an extra layer of safety.
Infants and Food Allergies
Food allergies frequently make their first appearance during infancy and early childhood, right when parents are introducing new foods. Babies are encountering these proteins for the first time, and their immune systems are still learning what's safe and what isn't.
Current research suggests that introducing allergenic foods early (around 4 to 6 months of age) may actually help prevent food allergies from developing in the first place. This represents a shift from older advice that recommended delaying certain foods. However, early introduction works best when guided by a pediatrician, or allergy specialist, particularly for babies who have eczema or a family history of allergies.
Signs of Food Allergy in Babies
Spotting food allergy symptoms in infants requires careful attention. Babies can't tell you their mouth feels tingly or their throat is tight, so you have to watch for physical signs instead.
After introducing a new food, look for:
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Hives or red, blotchy patches on the skin
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Swelling around the eyes, lips, or face
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Vomiting or excessive spitting up beyond what's normal
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Diarrhea, especially if it contains blood
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Unusual fussiness, crying, or irritability
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Wheezing, coughing, or labored breathing
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Sudden sleepiness or unusual lethargy
Any signs of breathing difficulty, severe swelling, or unresponsiveness call for emergency care right away. For milder symptoms, like a few hives or some extra fussiness, contact your pediatrician to discuss whether allergy testing makes sense.
Are Food Allergies Genetic?
Genetics do influence food allergy risk, though the relationship isn't straightforward. If a parent or sibling has any allergic condition like food allergies, eczema, asthma, or hay fever, then a child's chances of developing food allergies increase. The chances of developing food allergies seems to be higher for children who have eczema, possibly because allergens can enter the body through irritated skin.
That said, genetics don't tell the whole story. Plenty of children with strong family histories of allergies never develop them, while others with no family history do. Scientists believe that a combination of inherited tendencies and environmental factors ultimately determines who ends up with food allergies.
If allergies run in your family, talking with your child's doctor about early allergen introduction can help you make informed choices about when and how to introduce high-risk foods.
How to Test for Food Allergies
Accurate food allergy testing starts with a conversation. Your doctor will ask about your symptoms, when they occur, what you ate beforehand, and your medical history. This information helps determine which tests will give the clearest answers.
Several testing methods are commonly used:
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Skin prick testing: Small amounts of food proteins are placed on your skin, usually on the forearm or back. If you're allergic, a small raised bump appears within about 15 to 20 minutes. This test is quick and provides immediate results.
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Blood testing: A blood sample measures IgE antibodies to specific foods. Blood tests work well for people who can't do skin testing because of skin conditions, certain medications, or other factors.
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Oral food challenge: Often considered the most definitive test, this involves eating gradually increasing amounts of a suspected allergen under close medical supervision. It's done in a clinical setting where treatment is immediately available if a reaction occurs.
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Elimination diet: Removing suspected foods from your diet for several weeks, then reintroducing them one at a time, can help identify triggers. This approach works best with guidance from an allergy specialist or dietitian.
Your allergy doctor may combine several of these methods to reach an accurate diagnosis. Testing also helps distinguish true food allergies from food intolerances, which involve different body systems and require different management approaches.
Food allergy testing is generally reserved for patients with reactions consistent with food allergy. This is because there is a high rate of false-positives in food testing. Some clinics offer food panel testing to screen for mutliple food allergies at once, but the results are not considered reliable and can lead to unnecessary food restrictions.
Food Allergy Testing in Louisville and Kentuckiana
At Advanced ENT & Allergy, our board-certified doctors provide comprehensive food allergy testing at multiple locations throughout Louisville, Central Kentucky, and Southern Indiana. Learn more about allergy testing and what to expect during your appointment.
Food Intolerance Versus Allergy
A food allergy involves the immune system. Even tiny amounts of the trigger food can provoke symptoms, and reactions can be severe or life-threatening. With repeated exposures, reactions sometimes become more intense.
A food intolerance, on the other hand, typically involves the digestive system rather than the immune system. Symptoms often include bloating, gas, stomach pain, diarrhea, or nausea, and they tend to develop more slowly. Unlike allergies, intolerances are often dose-dependent: a small amount of the food might be fine, while a large amount causes problems. While food intolerances can be uncomfortable, they are not life-threatening like true food allergies.
If you're not sure whether you're dealing with an allergy or an intolerance, proper testing can help identify the cause and guide next steps.
We Are Food Allergy Doctors
Living with food allergies requires ongoing attention, but it doesn't have to mean constant worry. With an accurate diagnosis, clear guidance, and a solid management plan, most people with food allergies lead full, active lives.
At Advanced ENT & Allergy, our team specializes in identifying food allergy triggers and creating individualized care plans. Our doctors take time to answer your questions, address your concerns, and give you the knowledge you need to stay safe. Schedule an appointment today to get started.
