Science Weekly Food intolerances: how do you know if you have one?
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Apr 28, 2026 
Rebecca Seal, food and health journalist and author of Irritated, explains why at-home intolerance tests are popular but often misleading. She contrasts allergies and intolerances, examines common trigger foods, and recounts her own test-comparison experiment. Practical alternatives like careful elimination diets and professional advice are discussed.
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Rebecca's Home Testing Experiment
- Rebecca Seal ordered multiple at‑home intolerance tests and collected finger‑prick blood and hair samples at home on the same day to compare results.
- She deliberately ate a seven‑course meal two days earlier to see if recent consumption showed up on the tests, and it did.
Most At Home Intolerance Tests Lack Validation
- Most commercial intolerance tests (except lactose hydrogen breath tests) are not scientifically validated and produce junk results according to Rebecca Seal.
- She contrasted a gold‑standard ALEX2 allergy test (295 allergens) with consumer IgG and hair tests and got conflicting outcomes.
IgG Shows Exposure Not Intolerance
- Commercial blood tests often measure IgG antibodies, which indicate exposure and tolerance, not intolerance or allergy.
- True allergy testing uses IgE; IgG levels typically rise after eating a food and reflect normal immune memory.
