Food Allergy or Food Intolerance?How to Tell

Pizza on Friday, and by Saturday morning you’re bloated and in the bathroom. You blame the cheese, or the wheat, or the sauce. You’ve read that “everyone’s gluten-intolerant now” and you’ve seen the home test kits online. You’re half-ready to cut out half your kitchen.

Intolerance: a digestive problem

The NHS¹ lists symptoms such as diarrhoea, bloating, farting and tummy pain, which usually appear within hours of eating the food, plus headaches, fatigue, nausea, constipation, joint pain or rashes that can last hours to days. It names lactose as the most common intolerance, and others including gluten, histamine, caffeine, alcohol, sulphites, salicylates, MSG and benzoates.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)² defines lactose intolerance as digestive symptoms such as bloating, diarrhea and gas after consuming foods or drinks that contain lactose, caused by the small intestine’s inability to break down all the lactose. It says about 68 percent of the world’s population has lactose malabsorption, about 36 percent in the US, but only people who have symptoms are lactose intolerant. It stresses that lactose intolerance is different from a milk allergy, which is an immune system disorder. See dairy and bloating.

Allergy: an immune reaction

The NHS³ lists dizziness or lightheadedness, itchy skin or a raised rash, swelling of the lips and face, breathing difficulties, sneezing, nausea, stomach pain and diarrhea, and says reactions can come right away or days later. Most are not serious, it says, but severe reactions need emergency care for throat swelling, severe breathing trouble, confusion or fainting.

For anaphylaxis, the NHS³ says to use an adrenaline auto-injector or nasal spray immediately if you have one, and to call emergency services even if you or the person you’re with seems to be feeling better. Management means avoiding the allergen, checking food labels and restaurant menus carefully, carrying prescribed injectors and telling others. Antihistamines treat mild reactions.

Why it matters which one you have

An allergy can be dangerous, and the NHS¹ says an intolerance can’t cause a serious allergic response. They need different plans. Celiac disease is a separate question that needs testing before you remove gluten. See celiac disease and IBS.

How it’s worked out

For intolerance, the NHS¹ says a GP may suggest a diet that avoids the suspect food, blood tests, breath tests for lactose or a food and symptoms diary. It warns that home-purchased tests lack good evidence and risk unnecessary food elimination, and says never to restrict foods without professional guidance, since you risk nutritional deficiencies.

The play

Try this: a food and symptoms diary

For two weeks, write down what you eat and drink and when, and any symptoms, the time they began and how long they lasted. Note any hives, wheezing or swelling (allergy signs), and any purely digestive symptoms.

Don’t cut foods yet. Bring the diary to a clinician and ask which test makes sense.

When to get checked

Don’t wait if

1. Emergency

   Get emergency care for swelling of the lips, face or throat, trouble breathing, confusion or fainting after eating.

The NHS¹ says to see a GP if you have symptoms of a food intolerance that keep coming back, and if you think you may have a food allergy.

Book an appointment if any of these fit:

• You keep reacting after the same food
• You get bloating, diarrhea or pain within hours of eating
• You’ve had a rash, hives or swelling after eating
• You’re thinking of cutting a whole food group
• You’re considering a home test
• You’re not sure which one it is

Allergy or intolerance, the answer matters, and a diary plus a clinician beats a kit.