IgG vs IgE: Understanding Allergy and Immune Testing

A patient walked into my clinic a few weeks ago holding a printout, looking genuinely worried. Twenty foods flagged as “reactive.” Eggs, wheat, dairy, even coffee. She’d already cut half of them out before she’d even sat down in front of me. When I asked what kind of test she’d taken, she wasn’t sure. Turned out it was measuring IgG, not IgE, and that one detail changes everything. I get some version of this conversation almost every week, so I want to actually explain the IgG vs IgE difference properly, because most people have never had it explained to them at all.

Here’s how I usually walk patients through it.

IgE Is the Antibody You Actually Need to Worry About

IgE is what people picture when they think “allergy.” It’s fast. It’s obvious. There’s no mystery to it once it happens.

• Reactions show up within minutes, not hours
• You’ll see hives, swelling, wheezing – in bad cases, anaphylaxis
• Mast cells release histamine, and your body reacts hard and immediately
• This is the antibody we test for with skin prick tests or specific IgE blood work

If someone’s throat starts closing up after a bite of prawn, that’s IgE doing exactly what it’s built to do. It’s unmissable. It’s also the one that can genuinely kill someone, so it’s not the antibody to be casual about.

IgG Is a Completely Different Thing

This is where the confusion around IgG vs IgE really starts, and honestly, it’s understandable.

• IgG is just the most abundant antibody floating around in your blood
• It’s a normal, healthy record of what your immune system has met before
• Levels go up because you eat something often – not because it’s hurting you
• Seeing “high IgG to eggs” usually just means you eat a lot of eggs

That’s really the whole issue in one sentence. A high IgG number doesn’t tell you that a food is a problem. It tells you that you’ve been exposed to it. Those are not the same thing, even though the marketing around these tests tends to blur the line completely.

The Core Difference, Side by Side

I find a table makes this easier to hold onto than a wall of text:

That table isn’t just a technicality – it has real consequences. I’ve had patients cut out a dozen foods based on an IgG panel, spend months feeling restricted and anxious about eating, while whatever was actually causing their symptoms went completely uninvestigated.

When Is Each Test Worth Doing?

This isn’t just a technicality – it genuinely changes what happens next in your care.

IgE testing is worth it when:

• You’ve had a quick, repeatable reaction to a specific food
• Swelling, hives, or breathing trouble were involved
• You need to confirm (or rule out) a real allergy before trying an elimination diet
• A child’s known allergy needs monitoring over time

IgG testing usually isn’t the answer for:

• Working out why you feel bloated or intolerant to something
• Explaining ongoing fatigue or “foggy” days
• Deciding what to cut from your diet long-term
• Replacing an actual gut investigation

If what you’re dealing with sounds more like bloating, unpredictable bowels, or discomfort after meals, that’s rarely an antibody issue at all. More often it’s gut motility, your microbiome, or something like SIBO. I’ve actually written a bit more about this – how a proper gut health test can help identify what’s really going on – and it’s usually a far better starting point than an IgG panel.

What I Actually Tell People to Do

I always start with the history, not the lab work. Timing tells you almost everything. A reaction within minutes points to IgE and a true allergy. Something that builds slowly over hours or days points somewhere else entirely – usually the gut, not the immune system.

My honest advice, every time:

• Track food and symptoms yourself before paying for any test
• Ask exactly what antibody a test measures before you hand over money
• Don’t cut out major food groups on the strength of one report
• If a reaction is sudden and severe, get seen properly – don’t wait around for a private panel to arrive in the post

The gut-liver connection plays a much bigger role in these “mystery” symptoms than people realise, and it gets overshadowed constantly by tests that sound scientific but don’t actually hold up.

Where This Leaves You

Your immune system isn’t out to confuse you, even though it can feel that way. IgE and IgG simply do different jobs. One is your alarm system – fast, obvious, occasionally life-threatening. The other is more like a quiet logbook of what you’ve eaten, not a verdict on what’s hurting you.

Getting the IgG vs IgE distinction straight can save you years of unnecessary food restriction, and more importantly, it points you toward what’s actually causing your symptoms. If a food triggers something sudden and physical, get proper IgE testing done. If it’s more of a slow, digestive discomfort, the answer is almost always in your gut, not in an IgG report.

Want to Dig Deeper?

I dig into topics like this on the Liver & Guts Podcast most weeks – trying to cut through the noise around gut and liver health that doesn’t get explained well elsewhere.

And if you’re dealing with symptoms that just won’t resolve and want a proper look rather than another guessing game, you’re welcome to book a consultation with me here. You deserve real answers, not another restrictive diet built on the wrong test.