My kitchen table is littered with tiny test tubes, envelopes and plastic lancets. At one end of the table, I have a parcel containing everything I need to take a food intolerance blood test, sold by one of the best-known companies in this market, as well as one of their food and environmental allergy tests, a package deal that cost me just over £200.
At the other end, I’ve arranged everything I need to do a top-of-the-range ALEX2 allergy blood test, which I got from the allergy clinic run by Dr Helen Evans-Howells, a GP and allergy specialist who runs clinics in Hampshire, Belfast and online. This costs £295 and comprises two lancets, which I will soon be using to puncture tiny holes in several of my fingertips; a blood tube; disinfecting wipes; and a return envelope. In the middle of the table, I have a large bowl of hot water, in which my left hand is soaking. I’ve also cut off a lock of my hair, which is now in a sandwich bag ready to be sent to a lab tomorrow for bioresonance testing. My plan is to compare the three sets of results, all from samples taken on the very same day. Given that I don’t have any food or environmental allergies or intolerances, all three tests should show exactly the same thing: nothing.
My daughters are desperate to watch me draw my own blood, and I shoo them out of the room. The last time I did one of these home blood tests, for hormones, I started to feel faint and – as everyone else had gone to bed – had to put myself in the recovery position on my kitchen floor, while still attempting to collect the required 30ml of blood. I’m not looking forward to this, and I really do not want an audience.
It’s hard to know exactly how much we are spending on either home allergy or home intolerance tests, or how many of us are doing them, but, globally, allergy diagnostics (including hospital tests) generate about $5.3bn of revenue a year, and the at-home food sensitivity test market was valued at $2.6m in 2025.
If accurate, these numbers blow my mind, for two reasons. First, because in the absence of a clinician who knows your personal and family medical history, even the best kinds of allergy test results can be hard to read – and not all those on the market are the best kinds.
Second, because, apart from a hydrogen breath test for lactose intolerance and blood tests for coeliac disease, which are both used medically alongside biopsies, there is absolutely no evidence that any of the many different kinds of intolerance tests that we can buy online by ourselves – or via nutritionists, complementary or alternative healthcare practitioners – give us any useful information at all.
Both allergies and food intolerances can be horrible to live with, but they are very different conditions. About 6% of adults have a clinically confirmed food allergy, while about 24% of us report at least one intolerance.
There are two kinds of allergy: immediate IgE-mediated and delayed non-IgE (these cause mainly gastrointestinal symptoms, often hours or days after exposure, and can be really hard to diagnose as they do not show up in blood tests). IgE allergies happen when our immune cells misbehave and decide a harmless substance – such as dairy – is a threat. Once your body has made that mistake, your blood will contain a type of antibody called immunoglobulin E (IgE) to dairy.
IgE allergies include things such as hay fever and dust-mite allergy, and food allergies that cause symptoms from sneezing, coughing, rashes, swelling, vomiting, diarrhoea and breathing difficulties through to potentially life-threatening anaphylaxis. IgE blood tests can help doctors work out what you are allergic to, but only alongside a detailed medical history.
Food intolerances don’t involve the bit of the immune system that causes allergies. They happen when the body can’t digest certain foods properly; as a result, food intolerance symptoms mainly happen in the gut. The most common causes of food intolerances are gluten, lactose, dairy and sulfites but, just as with allergies, almost any food can cause an intolerance.
All intolerance tests are junk, and all should be banned. None of the home intolerance tests on the market are accurate, science-backed or endorsed by any mainstream health bodies. The only way – sadly – to determine if you have a food intolerance (or a non-IgE allergy) is an exclusion diet followed by retrialling whatever you stopped eating to see if it really is connected to your symptoms.
double quotation markI don’t think you can diagnose people with an intolerance, then say – in the small print – you’re not doing that, without looking like a charlatan
Equally, it should not be as easy as it is to buy an allergy test; although allergy tests are more scientifically rigorous, they are not all equal, and even the best allergy tests carry the risk of giving a false positive if you don’t do them with a clinician to guide you. This is especially problematic if you have a child with eczema, says Professor Helen Brough, consultant in paediatric allergy at the Evelina London children’s hospital. “In children with eczema, if you do IgE tests, the results for many foods will come back slightly positive because that’s what happens when you have eczema: you have a high total IgE.”
Probably the most commonly purchased food intolerance test is a fingertip blood IgG test, which looks at the levels of IgG (immunoglobulin G) in our blood. But IgG has nothing to do with food intolerances (or allergies). As the British Dietetics Association says, “IgG are normal antibodies found in the body in response to infections, and the production of these antibodies is a normal response to eating food.” We make IgG antibodies to every single food we consume.
When I talked to Theresa MacPhail, a medical anthropologist and author of Allergic: How Our Immune System Reacts to a Changing World, she was furious about IgG tests. “IgG tests are worthless,” she says. “Everybody who drinks a glass of milk is going to have an IgG antibody response because it’s a foreign protein. People are shelling out $500 to say that their bodies are digesting milk. Food allergy specialists hate them and have told me repeatedly, off the record, they are nothing more than expensive snake oil. More than one said they should be banned. I don’t blame the average person for trying to figure out their discomfort; I blame the corporations offering them and the lack of regulation.”
Having an IgG response to anything in your bloodstream just shows that you have eaten it recently. In 2018 Shayla Love, then a writer for Vice magazine’s Wellness Lies section, gave up peanuts, oats, almonds and egg whites after an IgG intolerance test told her she should. Months later, when she took another IgG test, those “intolerances” didn’t show up, but the foods she’d added to her diet to make up for those she’d removed did: walnuts, sunflower seeds and cashews, which she had begun to eat in large amounts (with no dire consequences) only after giving up everything from the previous test.
In fact, MacPhail tells me, “IgG actually seems protective of food allergies, so people who have a high IgG response to something don’t have the IgE response.” Studies have also shown that during oral immunotherapy for allergies (a medically supervised treatment in which tolerance to an allergen is built up gradually by consuming very low doses), our levels of IgG in response to it rise as we become more tolerant. But, as I have found from talking to (and arguing with) multiple nutritionists, during their training, they are sometimes taught that a high IgG response means you are intolerant of a food.
If you’ve ever taken an IgG test, you might not have noticed that many of the companies provide a disclaimer written in very small type that more or less agrees with what allergists and the British Dietetic Association say about the role of IgG in allergies. These disclaimers say that the testing company “does not claim to treat or cure”, that the link between IgG levels and food intolerance symptoms “is not well understood” or that their tests, results and supporting information “should not be treated as a medical diagnosis”.
I don’t think you can diagnose people with an intolerance and then say – in the small print – that you’re not diagnosing people with an intolerance, without looking quite a lot like a charlatan.
After soaking my hand in warm water, making sure I am hydrated and whirling my arm around like a centrifuge to increase blood flow, I manage to draw the blood without passing out this time. I have to use the lancets on four different fingers, but I get the amount I need into each tiny vial, package them up and send them off in the post next day, along with the bag full of hair. (The hair test takes longer to come back, and in the interim I get emails offering a testing upgrade: for a mere £20 – reduced from £49, of course – I can also find out about my inflammation levels, skin health, ageing status and sleep hormones. I decline the opportunity.)
A day later, Dr Evans-Howells emails me my allergy test results – “All normal!” – and several pages of negative results. I’m totally unsurprised to learn that I have no allergies and no IgE in my blood to any allergen.
But I get different results when my food intolerance tests come back. According to them, I shouldn’t eat eggs or dairy, and I also have noticeable IgG responses to cardamom, bay leaf, cuttlefish, mulberry, rooibos, camomile, green tea, juniper, tapioca and venison. That’s a pretty random list of foods, except that I deliberately took the IgG test after taking my husband out for a very fancy birthday lunch, just to see if any of the many unusual ingredients from the meal turned up. And they did: everything on the list apart from sugar cane, green tea and eggs was on the menu.
I eat at least one egg almost every day (at lunchtime I race home from my rented office down the road, scramble an egg, park it on toast, then race back so I can work as much as possible before my kids finish school). I top my porridge – made with milk – with unrefined brown cane sugar, and I drink so much green tea that I’m trying to cut back, as it’s stopping me from sleeping.
My IgG results simply reflected what I’d eaten most recently, and as some of what I’d eaten was pretty unusual, my results were unusual, too. That’s as it should be: we make IgG as a totally normal response to eating any food.
Photograph: Kellie French/The Guardian
I can hardly bring myself to write about the results of the hair test. They arrive via email, along with another offer to test my hair sample further and a jaunty letter from the founder, who has a BSc and a health-coaching qualification. The email tells me to “minimise [my] consumption of high-reactivity items as much as possible”. That means no more apples, almonds, coconut or banana, in any form – plus I’m apparently very sensitive to environmental allergens including bees, European beech, laburnum, primrose, tamarisk and wallflowers, as well as highly reactive to metals including iridium and sulphur, and the additives E141 (natural green food colouring), E150 (caramel food colouring), E170 (calcium carbonate) and E307 (alpha-tocopherol, a food additive and a form of vitamin E). Iridium is 40 times rarer than gold, and is used as an alloy in platinum jewellery, electronics manufacturing, spark plugs and radiotherapy. I have probably never even come into contact with it.
I’m supposedly moderately reactive to a massive list of things – the “lab” tests for sensitivities to 900 items, so it’s not surprising that the hit rate is high – and they recommend removing these from my diet for four to six weeks, once I’ve cut out the high-reactivity items. This would mean cutting all wheat products, dairy (from cows, sheep and goats), all mushrooms, corn, peanuts and eight more E numbers.
This, to use the correct scientific term, is bullshit.
IgG tests and all other general intolerance tests have no scientific basis to them, and they are not the same as the IgE allergy tests used by the NHS. Clinical IgE allergy tests tend to be given out very sparingly, are carried out by centralised and regulated labs, and, assuming they’ve been ordered by an allergy specialist, are interpreted by someone highly trained. There are no accurate tests for any intolerances, apart from lactose intolerance (if you can’t digest lactose, you breathe out a lot of hydrogen, which can be measured by a doctor).
Unlike dietetics, which is regulated, nutritional therapy – like almost all complementary and alternative therapies in the UK, as well as things such as counselling and coaching – is not. So although there are some brilliant and extremely ethical and knowledgable nutritionists and nutritional therapists out there, it can be hard to tell which are the good ones. Most of us lay people don’t even know the difference between registered dietitians, who are part of a legally regulated healthcare profession, registered nutritionists, who need a degree-level qualification and to be on the UK Voluntary Register of Nutritionists, and nutritional therapists or coaches, who are basically unregulated.
You can set yourself up as a nutritional therapist, nutritionist or health and nutrition coach with no training whatsoever. Or, if you do want some training, there’s no shortage of quickie options: I found one nutritional therapy course that takes two and a half hours online and costs £18. Another, which appeared on the first page of Google results, costs £225 and takes 50 hours – just six and a half days to get to grips with something as complex and nuanced as human nutrition. (The syllabus covered everything from vitamins and minerals to digestion and disordered eating.) And then there are postgraduate qualifications, which require a bachelor’s degree in nutritional science before you can even start, and three-year, degree-level courses you can’t complete without evidence of 200 hours of clinical practice.
double quotation markPeople often go to a nutritional therapist because they’re not getting face time with their doctor. So they’re already in a vulnerable position
I wanted to know what kind of training nutritional therapists get about intolerance testing. So I asked Sam Ratanji, a nutritional therapist who happens to be allergic to peanuts and tree nuts, whether her three-year course included much on how or whether to test her clients. She is a chef as well as a therapist, running her own business focusing on what individuals can and should eat, rather than using lab tests or recommending supplements in the first instance.
“I never recommend pulling anything out of the diet unless there is a very good reason to do so,” she says. “And even then, it would only ever be short-term, unless we were advised by a doctor that it is needed.” She says the push to use IgG tests doesn’t necessarily come from nutritional therapy lecturers, but rather from the test providers themselves. “A lot of fairs take place at the colleges and the testing companies are always there, giving away freebies, along with free continual professional-development (CPD) training hours, in order to sell their products. They offer a really good webinar for students and graduates, but the reason they’re doing it is to sell their tests.” CPD hours help students learn more, and are required for students to join many membership bodies. Students often have to pay to complete their required hours, so these free courses are, of course, particularly attractive. The testing companies may also pay the colleges to be at the fairs.
Ratanji says her clients want to be tested for intolerances, but usually don’t understand how uncomfortable true intolerances are. “When I cook at events, nine times out of 10 I’ll be given a list of intolerances in advance to cater to. Because they’re intolerances, not allergies, I’ll prepare alternatives for the relevant people, but I won’t exclude things such as dairy or gluten completely for other attenders, and I make sure those with intolerances are aware these foods will be present on the table. Sure enough, it’s common for me to see the people who say they have intolerances choosing to eat the food from sharing plates containing the ingredients they said they couldn’t eat.”
Ratanji recently had a client whose daughter was having severe gastrointestinal symptoms. “She pushed for me to do IgG intolerance and gut-testing, and I pushed back, asking her why she was so adamant. It turned out she’s studying at the same college I trained at. She said, ‘I spoke to the companies who are part of the fairs there, and it feels like the responsible thing to do.’”
Like many of us, this mother had bought into the idea that IgG really can tell us what’s happening in the body from a scientific point of view – and why wouldn’t she, as that’s literally what the websites selling the tests claim, peppering their marketing with phrases such as “antigen-antibody complex” and “advanced immunoassy microarray technology”?
It gets worse. “Some of the intolerance testing companies give therapists kickbacks of £10 or £30 per test, so some make quite a lot of money from testing,” Ratanji says. “I don’t think that’s right, because we shouldn’t be selling anything to anybody who doesn’t need it. By the time somebody gets to a nutritional therapist, often it’s because they’re not getting answers from their doctors – because doctors are time-poor and they can’t get enough face time with them. So they’re already in a vulnerable position. It’s the nutritional therapist’s responsibility to not take advantage of that.”
This makes me so sad, and so angry. Thousands of people buy IgG intolerance tests every year, online and from trained and qualified practitioners, then make decisions about their own or their children’s diets because of them, believing they are valid, safe and based on scientific research and evidence.
Cutting foods out of our diets when we don’t need to can have life-changing consequences, particularly in small children whose immune systems are still learning to tolerate common foods, and in both kids and adults who have eczema and are therefore already at higher risk of developing a food allergy. In such cases, cutting out, say, dairy or gluten can actually make developing a food allergy more likely – it’s as though the immune system forgets that a food is safe to eat. One study followed 298 children in Chicago who had been on exclusion diets (mainly avoiding milk, egg, soy or wheat) to try to control their eczema. At the beginning of their diets, none of the kids had any IgE food allergies, but 54 of the children had immediate allergic reactions to their eliminated foods when they were reintroduced. In 14 cases, the immediate reaction was anaphylaxis. Multiple studies have had similar results. Unnecessary dietary restrictions can also trigger disordered eating and cause nutritional deficits and growth delays, especially in children. In addition, they can slow down the diagnosis and treatment of other conditions, which often turn out not to be related to diet at all.
There is no shortage of positive reviews for IgG tests (and for some of the other, madder, tests) if you start hunting for them, and every website showcases testimonials from people who say their lives have been changed because they gave up beef, oranges, tuna, milk and strawberries. I’d love to know how many, if any, tests are returned with a normal result. From a marketing point of view, it sort of behoves them, doesn’t it, to give us some kind of diagnosis – something rather than nothing? If everyone was leaving reviews saying, “This test told me nothing was wrong”, the companies would all be out of business.
The online intolerance blood-test package I bought also included an IgE allergy test, and its results were almost as interesting as my pseudo-intolerances. The unfortunate truth is that allergy blood tests – even the good ones – are not as reliable or as useful as we would like them to be, which is why so many allergy patients come up against doctors who seem frustratingly reluctant to run tests, especially for multiple allergens.
All that an IgE blood test can do is tell whether you are sensitised to an allergen. It can’t tell you whether you will ever react to it or if you ever have, and it can’t tell you anything about the severity of a possible reaction, either. Around 15-20% of us have IgE antibodies to foods in our blood, but this only turns into a food allergy for about 6% of people.
The test I did via Dr Evans-Howells’s clinic was the ALEX2 test, an enzyme-linked immunosorbent assay (or Elisa). This is a type of lab test used to check biological samples for things such as hormones or antigens. It’s probably the best test available, and I used it as a control; as expected, it showed that I’m allergic to nothing. The ALEX2 covers 295 food and environmental allergens and, at £295, it costs about three times as much as many of the other IgE tests you can buy online.
The cheaper IgE test I bought online looked at just under 50 food and environmental allergens. The company I used says its IgE tests are equivalent to those used by the NHS, but the website doesn’t explain how. It flagged me as reactive to oranges, almonds and cladosporium, a common indoor and outdoor mould.
Without the ALEX2 test as a control, it would have been incredibly easy for me to assume that I really do have a problem with oranges and almonds, and to start worrying about whether it was safe to eat them – something I’ve seen dozens of people grappling with online. Your toddler may never have reacted to prawns, or pistachios, or coconut, but if a test you’ve done on their blood tells you they might, then of course it would feel foolhardy to serve them those foods.
It would be wonderful if you could just run a test on a baby before they even start eating food and get a printout of all their allergies or intolerances. But allergies and intolerances are way more slippery than that. We are not born with them; they develop over time and because of an incredibly complex and constantly evolving dance involving our immune systems, our genetic inheritance and how our environments interact with them. So we can’t just take a snapshot of our blood, skin or hair and instantly know what our allergy outlook for life is.
I wish this wasn’t true. I have lost count of the number of individuals struggling to work out their own diagnosis, and parents I have talked to about the horror show that is trying to work out what is causing their child’s reactions, and whether those reactions are even allergies at all. These people are exhausted. They would do anything to protect their child and are desperate to work out what is causing them pain.
The mental health costs of this acute stress are obvious and measurable: the Natasha Allergy Research Foundation’s 2024 survey found that 83% of people living with allergies feel that it significantly impacts their overall mental health and emotional wellbeing, with 42.51% saying this impact was very significant. There is a clear bidirectional relationship between mental health and food intolerances, too. So it would be great if we could do a skin-prick test, or a blood test – or any kind of test – and get back a piece of paper explaining what is going on and what we should do next. We can’t – but there are plenty of companies who are happy to pretend that we can.
This is an edited extract from Irritated: The Allergy Epidemic and What We Can Do About It by Rebecca Seal, published by Headline Home on 24 April at £22. To support the Guardian, order your copy at guardianbookshop.com
