When you have a bad reaction to food, it can be confusing to know exactly what's happening in your body. Is it a food allergy? An intolerance? A sensitivity? These terms are often used interchangeably, but they actually describe very different responses in your body.
Understanding the distinctions matters because the severity, timing, testing methods, and management strategies differ significantly for each type of reaction.
This guide explains what U.S. government health agencies tell us about these different types of food reactions.
Food Allergies: Immune System Involvement
What Are Food Allergies?
According to the Food and Drug Administration (FDA), a food allergy is a medical condition in which exposure to a food triggers a harmful immune response. The FDA notes that food allergies occur when the body's immune system recognizes a food protein as harmful and triggers a protective immune system response.
Symptoms of Food Allergies
Food allergy symptoms typically appear quickly—within minutes to two hours after eating the problem food.
Common symptoms include:
- Hives or skin rash
- Swelling of lips, face, tongue, throat, or other body parts
- Wheezing or difficulty breathing
- Abdominal pain, diarrhea, nausea, or vomiting
- Dizziness or lightheadedness
- Anaphylaxis (severe, life-threatening reaction requiring immediate emergency care)
The "Big Nine" Allergens
According to the FDA, more than 170 foods have been reported to cause allergic reactions, but the FDA identifies nine major food allergens that account for most serious allergic reactions:
- Milk
- Eggs
- Fish (bass, flounder, cod, etc.)
- Crustacean shellfish (crab, lobster, shrimp)
- Tree nuts (almonds, walnuts, pecans, etc.)
- Peanuts
- Wheat
- Soybeans
- Sesame
The FDA requires food manufacturers to clearly label these major allergens on packaged foods.
Testing for Food Allergies
Healthcare providers can diagnose food allergies through:
- Skin prick tests
- Blood tests (measuring specific antibodies)
- Oral food challenges (eating the suspected food under medical supervision)
Management
The FDA emphasizes that the only way to prevent an allergic reaction is to avoid the food completely. For severe allergies, carrying emergency epinephrine (EpiPen) is essential.
Food Intolerances: Digestive System Issues
What Are Food Intolerances?
Food intolerances occur when the body has difficulty digesting certain foods. Unlike allergies, intolerances don't involve the immune system.
Lactose Intolerance
According to the NIH Office of Dietary Supplements, lactose intolerance is caused by a deficiency of the enzyme lactase, which breaks down lactose (milk sugar).
The NIH notes that people with lactose intolerance can often tolerate small amounts of dairy without symptoms and that symptoms typically occur 30 minutes to 2 hours after consuming dairy products.
Symptoms of lactose intolerance:
- Gas
- Bloating
- Diarrhea
- Abdominal cramps
- Nausea
Other Common Intolerances
Gluten intolerance (Non-Celiac Gluten Sensitivity) - Different from celiac disease (an autoimmune condition). Symptoms may include digestive discomfort, headaches, and fatigue.
FODMAPs intolerance - Difficulty digesting certain fermentable carbohydrates (explained more in detail: FODMAPs = Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols - types of carbs that can cause digestive issues).
Sulfite sensitivity - Reaction to sulfites used as preservatives in food.
Symptoms of Food Intolerance
Food intolerance symptoms:
- Usually affect the digestive system
- Are dose-dependent (more food = worse symptoms)
- May take several hours to appear
- Are rarely life-threatening
- Can sometimes be managed by eating smaller amounts
Testing for Intolerances
Lactose intolerance can be diagnosed through:
- Hydrogen breath test
- Lactose tolerance test
- Stool acidity test (for infants and young children)
For other intolerances, elimination diets followed by reintroduction are often the primary diagnostic tool.
Management
Many people with food intolerances can:
- Consume small amounts without symptoms
- Use enzyme supplements (like lactase pills for lactose intolerance)
- Find acceptable alternatives
- Gradually build tolerance in some cases
Food Sensitivities: The Gray Area
What Are Food Sensitivities?
Food sensitivities (or non-immune food reactions) are the least understood category. They may involve immune responses that aren't detected by standard allergy tests, or they may involve other body processes that aren't fully understood.
Characteristics of Food Sensitivities
Food sensitivities typically:
- Have delayed onset (hours to days after eating)
- Cause less severe symptoms than allergies
- May involve body responses not detected by standard allergy tests
- Are highly individual
- Can be dose-dependent
Common Symptoms
Digestive symptoms:
- Bloating
- Gas
- Diarrhea or constipation
- Abdominal pain
Whole-body symptoms:
- Headaches or migraines
- Fatigue
- Brain fog (difficulty concentrating or thinking clearly)
- Joint pain
- Skin issues (eczema, rashes)
- Mood changes
Testing for Sensitivities
Standard medical testing for food sensitivities is limited. Some tests (like IgG testing) are controversial and not recommended by government health agencies.
The most reliable method is:
- Systematic food and symptom tracking for 4-6 weeks
- Elimination diet (removing suspected foods)
- Reintroduction testing (one food at a time)
Key Differences at a Glance
TIMING:
- Allergies: Immediately to a few hours
- Intolerances: 30 minutes to several hours
- Sensitivities: Hours to days
IMMUNE SYSTEM:
- Allergies: Yes (specific type of immune response)
- Intolerances: No
- Sensitivities: Possibly (different type of immune response or other mechanisms)
SEVERITY:
- Allergies: Can be life-threatening
- Intolerances: Uncomfortable but not dangerous
- Sensitivities: Usually mild to moderate
AMOUNT MATTERS:
- Allergies: Even tiny amounts can trigger reaction
- Intolerances: Dose-dependent (amount matters)
- Sensitivities: Often dose-dependent
TESTING:
- Allergies: Skin prick tests, blood tests, food challenges
- Intolerances: Breath tests, elimination diets
- Sensitivities: Elimination and reintroduction tracking
The Importance of Tracking
For all three types of reactions, systematic tracking is valuable—but it's especially critical for sensitivities and intolerances where delayed reactions make identification challenging.
What to Track
- All foods and beverages with ingredients and portions
- All symptoms with severity, timing, and duration
- Medications and supplements
- Other factors (stress, sleep, exercise, menstrual cycle)
Why Tracking Works
According to the Dietary Guidelines for Americans, understanding your individual dietary patterns and their effects on your body is important for making informed food choices. Tracking provides objective data about connections between foods and symptoms.
Tools that specialize in food and symptom tracking can automatically correlate foods consumed within an adjustable time window before symptoms occur, making it easier to identify patterns—especially for delayed reactions.
Nutrition Considerations
Whether you have allergies, intolerances, or sensitivities, eliminating foods from your diet raises nutritional concerns.
The Dietary Guidelines for Americans emphasize that "nutritional needs should be met primarily through foods and beverages." When avoiding foods or food groups, ensure you're getting essential nutrients from other sources.
Key Nutrients to Monitor
If avoiding major food groups, pay attention to:
Dairy-free:
- Calcium (RDA: 1,000-1,200 mg/day per NIH ODS)
- RDA = Recommended Dietary Allowance (the amount most people need daily)
- Vitamin D (RDA: 600-800 IU/day per NIH ODS)
- Vitamin B12 (RDA: 2.4 mcg/day per NIH ODS)
Gluten-free:
- Fiber (22-34 g/day per Dietary Guidelines)
- B vitamins from enriched grains
- Iron (RDA: 8-18 mg/day per NIH ODS)
Multiple food elimination:
- Consult with a registered dietitian to ensure nutritional adequacy
Tools that automatically calculate nutrient intake using USDA databases can help ensure you're meeting these requirements.
When to See a Doctor
Seek medical evaluation if you experience:
- Immediate, severe reactions after eating (seek emergency care immediately)
- Frequent digestive problems affecting quality of life
- Unintended weight loss
- Symptoms that worsen despite dietary changes
- Need for allergy testing
- Concerns about nutritional deficiencies
Bring your tracking data to medical appointments. According to healthcare standards, documented patterns help clinicians make more accurate diagnoses.
The Bottom Line
Food allergies, intolerances, and sensitivities are three distinct types of adverse food reactions:
- Food allergies involve the immune system, appear quickly, can be life-threatening, and require complete avoidance
- Food intolerances involve digestive difficulties, are dose-dependent, and can often be managed with smaller portions or enzyme supplements
- Food sensitivities are less well-defined, have delayed onset, and are best identified through systematic tracking and elimination testing
Understanding which type of reaction you're experiencing helps you choose the appropriate testing, management strategy, and level of dietary restriction.
Need help identifying which foods affect you? Track Change Thrive analyzes your food and symptom patterns using proprietary correlation algorithms, tracks nutrients against NIH standards, and flags allergens and ingredients you want to avoid. Start your free 7-day trial.