If someone at Thanksgiving claims they can't have stuffing because they're "sensitive" to gluten, you probably can't prove them wrong. A food "sensitivity" just means you sometimes have a bad reaction to it.

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A food allergy is different. Here are some signs someone doesn't really have a food allergy:

  1. The only symptom they ever have is an upset stomach. Real food allergies tend to involve things like hives, difficulty breathing, and trouble swallowing. If they just feel sick sometimes, it might be an intolerance, but it's probably not an allergy.
  2. Their symptoms come on gradually. If you're intolerant or sensitive to a certain food, it can take up to an hour to feel sick from it. But an allergic reaction usually happens within minutes or even seconds.
  3. Sometimes they can eat it and they're fine. If it's a real allergy, they'll have the same reaction every time.
  4. They can eat a little of it, just not a lot. With a real allergy, even a tiny bit causes a reaction. And it doesn't matter how it's prepared, or if it's raw or cooked.

Read more at Prevention.