Why the Distinction Matters More Than Most People Realise
"I got tested for food allergies and everything came back negative — so food isn't causing my skin problems." This conclusion, drawn by millions of people and reinforced by well-meaning doctors, is based on a fundamental misunderstanding. Food allergies and food sensitivities are different conditions driven by different immune pathways, tested differently, and with completely different timelines. A negative allergy test does not rule out a food sensitivity. In fact, for acne, eczema, and IBS, food sensitivities are far more commonly the culprit than true food allergies — and standard allergy tests do not detect them.
True Food Allergies: IgE-Mediated
A true food allergy involves IgE antibodies — immunoglobulin E — which are part of the body's rapid defence system. On first exposure to an allergen, the immune system produces allergen-specific IgE antibodies that bind to mast cells in tissues throughout the body. On re-exposure, IgE triggers immediate mast cell degranulation and histamine release.
Key characteristics of IgE food allergies:
- Onset: 15 minutes to 2 hours after eating
- Symptoms: hives, swelling, vomiting, potentially anaphylaxis
- Threshold: often very small doses trigger a reaction
- Detectable: skin prick tests and specific IgE blood tests (RAST) reliably identify these
- Common allergens: peanuts, tree nuts, shellfish, fish, milk (IgE-mediated), eggs, wheat, soy
Food Sensitivities: IgG and T-Cell Mediated
Food sensitivities operate through entirely different pathways. IgG-mediated reactions involve immune complex formation — IgG antibodies binding to food antigens and forming complexes that activate complement and trigger inflammation. T-cell mediated reactions (Type IV hypersensitivity) involve memory T-cells that recognise food proteins and generate cytokine-driven inflammation. Both are slow, building over hours.
Key characteristics of food sensitivities:
- Onset: 6 hours to 72 hours after eating — often the next day or later
- Symptoms: skin inflammation (eczema, acne), gut symptoms (IBS-like), fatigue, brain fog
- Threshold: often dose-dependent — small amounts fine, regular or large amounts trigger reactions
- Not detected: standard IgE allergy tests are negative; commercial IgG tests exist but are controversial in clinical practice
- Common triggers: dairy, gluten, eggs, soy, nightshades, histamine-rich foods — but highly individual
Why People Get Negative Tests and Still React
Standard allergy panels test for IgE. They are designed to rule in or out anaphylaxis risk. They are not designed to detect — and cannot detect — the IgG or T-cell mediated reactions that drive most delayed food-triggered skin and gut symptoms. A negative allergy panel means "you do not have anaphylaxis-risk allergies to these foods." It says nothing about food sensitivities.
This is why the recommendation to "get tested for food allergies" before managing dietary eczema or acne is only partially useful. Allergy testing is important for safety (identifying anaphylaxis risks). But for delayed trigger identification, systematic food tracking and elimination is the practical gold standard — because it tests what actually happens in your body, not what antibodies are present at one point in time.
FODMAP Intolerances: A Third Category
FODMAP intolerances (relevant for IBS) are not immune-mediated at all. They are fermentation-based: certain carbohydrates are not fully absorbed in the small intestine and pass to the colon where bacteria ferment them, producing gas and osmotic effects. No antibodies are involved — a negative allergy test is expected. Identification requires low-FODMAP elimination and systematic reintroduction of individual FODMAP groups.
How Sensio Solves This
Because food sensitivities are delayed (6–72 hours), dose-dependent, and individual, they cannot be identified by a blood test — they can only be identified by observing what actually happens in your body. Sensio logs your meals by photo with timestamps and tracks symptoms across the correct 72-hour delayed reaction window. Over weeks of data, the foods that consistently appear before your acne, eczema, or IBS symptom events become statistically visible — this is your personal sensitivity map, built from your own responses, not a generic antibody panel.
FAQ
Are IgG food sensitivity tests reliable?
Commercial IgG food sensitivity tests have significant controversy in the medical literature. IgG antibodies to food antigens are a normal immune response to food exposure — their presence does not necessarily indicate intolerance. Most gastroenterology and allergy bodies do not recommend them as diagnostic tools. Systematic elimination and food logging remains the validated approach for identifying delayed food sensitivities.
Can I have both a food allergy and a food sensitivity to the same food?
Yes. Some people have both an IgE-mediated immediate reaction and a delayed IgG or T-cell reaction to the same food, producing both fast symptoms and slower inflammatory effects. Your allergy specialist can identify the IgE component; tracking identifies the delayed component.
Related Reading
Medical Disclaimer: Educational only; consult an allergist or gastroenterologist for diagnosis.
A negative allergy test is not the end of the story. Sensio finds the delayed food sensitivities that standard testing misses — using your own body's responses as the evidence.