Signs of a Food Allergy vs. a Food Intolerance
Updated 7 October 2026
Two different things, often confused
"My baby doesn't react well to X" can mean very different things — an allergy and an intolerance involve different body systems, different timelines, and different levels of urgency.
Food allergy
An allergy is an immune-system reaction, and it usually appears quickly — within minutes to two hours of eating the food. Signs include:
- Hives or a raised, itchy rash
- Swelling of the lips, face, or eyes
- Vomiting shortly after eating
- In severe cases, difficulty breathing or wheezing
A severe allergic reaction (anaphylaxis) is a medical emergency — call emergency services immediately if you see swelling of the face/throat or breathing difficulty.
Food intolerance
An intolerance doesn't involve the immune system, tends to come on more slowly (hours, sometimes up to a day or two later), and is generally less dangerous, though still uncomfortable. Signs include:
- Bloating, wind, or stomach cramps
- Diarrhoea or changes in bowel movements
- Skin irritation that develops slowly rather than suddenly
- General fussiness after eating, without the sudden rash/swelling pattern
What to do either way
Keep a note of what was eaten, when, and what happened — timing is one of the most useful clues for your health professional in telling the two apart. For anything beyond a mild, one-off intolerance-type reaction, or any suspected allergy, talk to your GP or health visitor rather than trying to diagnose it yourself; they may refer you for allergy testing if needed.
Don't self-exclude foods long-term without advice
It's tempting to just stop offering a food that seemed to cause a problem — but unnecessarily cutting out food groups (especially dairy or wheat) without medical guidance can affect your baby's nutrition. Get it checked first.
