Food Sensitivity, Intolerance & Allergies: What they are, and how to test for them


People with allergies or intolerances to food generally have to study lists of ingredients and change their eating habits accordingly. Though that is tough, a bigger challenge, however, is finding out what you can't tolerate at all. Today, we break down how to do it.

Harvard scientists recently evaluated 2.7 million American patient files. Their result: around four percent of people suffer from a food allergy [1]. Food intolerances are much more common - around 10 percent of people are affected by them [2]. Lactose intolerance is particularly common worldwide [3].

Those affected have to study ingredient lists carefully so as not to experience a nasty surprise after dinner, which can range from a rumbling tummy to violent flatulence to rashes, dizziness, and anaphylactic shock. And it is not always easy to associate certain foods with the symptoms. The upshot is some people may end up not finding out what is wrong with them.

In this article, you will learn what happens to your body when you have a food allergy, the symptoms that indicate an allergy, and how you can track it down with a blood test and targeted diets. You will also learn about types, symptoms, and treatments of food intolerances. Want to know the merits of food a sensitivity test vs allergy tests? We’ll get into that here as well.

What is a food allergy?

When you have an allergy, your immune system reacts to a harmless substance. The substances that can trigger allergies are called allergens. These are different proteins that occur, for example, in pollen, in animal hair, the excrement of house dust mites and, of course, in food.

Food Allergy and Sensitivity Testing from cerascreen

What happens in your body when you have an allergy?

An allergy always begins with sensitivity to an allergen. This means that the body produces excessive amounts of what are known as IgE antibodies. These immunoglobulins (this is what the “Ig” stands for) are each specialized in keeping certain intruders out of the body. For example, the immune system fights bacteria, viruses, worms, and, unfortunately, harmless allergens.

The IgE antibodies bind to receptors on the mast cells—cells from your immune system. Laboratories can determine the increased number of IgE antibodies in the blood and assign the antibodies to the corresponding allergens—this is how an allergy test using a blood sample works. If you come into contact with the allergen again, the allergen docks onto the IgE antibodies and causes the mast cell to release messenger substances such as histamine. The histamine promotes inflammation and thereby triggers the various allergic symptoms. If this process causes a sensitization as well as the emergence of symptoms, then you have an allergy on your hands [4, 5]

What happens during an allergic reaction?

Types of food allergies

Experts distinguish between different types of allergies. The most common form of allergy is the immediate type, allergy type I, which also includes food allergies. The reaction occurs immediately after you have consumed the allergen. Someone who is allergic to peanuts will experience symptoms such as a furry tongue and a rash a few seconds to 20 minutes after eating [6]. Delayed reactions are also possible, which cause another allergic reaction four to six hours later. 

FYI: some food allergies go away on their own in adulthood. Milk, egg, soy, and wheat allergies, for example, mostly affect children and disappear again in 90 percent of cases. However, allergies to nuts, fish, and shellfish usually last an entire lifetime [7].

How does a food allergy develop?

Today, allergies are referred to as "widespread disease". The number of allergic diseases has increased steadily over the last few decades. Scientists are still not quite sure why this is. A popular explanation is the hygiene hypothesis, which attributes the spread of allergies to our modern lifestyles, which separate us from dirt and germs[8]. But genetic factors may also play a role.

Are allergies inherited?

As a rule, nobody is born with an allergy. But people can have an inherited susceptibility to allergies. This often applies to allergies in general, i.e. the children of parents with hay fever are susceptible to all allergies, whether to pollen, animal hair, or food. This also applies to other so-called topical diseases that are closely related to allergies and often occur together with them, especially neurodermatitis and asthma [2, 7, 9].

FYI: As an infant, the womb is our home, which means it influences how our bodies develop. As a result, a mother's diet can also influence the development of allergies. A cesarean section and the age of the mother also seem to increase the risk of developing a food allergy [7].

Age Ranges of people living with allergies

Does dirt protect me against allergies?

The hygiene hypothesis is based on one observation: allergies are particularly common in cities and are much less common in children who have grown up on a farm.

According to the theory, our immune system rarely encounters foreign bodies such as pathogens, worms, and parasites in the hygienic environments in which we live in the Western world. When the immune system has nothing useful to do, it begins to use its strength to defend itself against harmless substances such as food and pollen [2, 8, 10].

FYI: Whether we develop an allergy is decided in the first few months of life, maybe even in the womb. So it depends on the infant's environment at the beginning of their life. In other words, holidays on a farm later in life will unfortunately not prevent allergies.

What role does the gut play in the development of allergies?

The intestinal flora (also called the microbiome) is a term that describes the composition of the billions of bacteria that live in our intestines. This microbiome plays a key role in how our immune system develops from early childhood. Researchers suspect that our modern way of life affects the intestinal bacteria, which in turn have an influence on the development of allergies [11].

A study from Estonia showed that Estonian children who still frequently grow up on farms and spend a lot of time outside have a significantly better bacterial colonization of the intestines than children from Sweden, who tend to grow up in urban environments [12].

Does breast milk protect against allergies?

For the immune system to develop healthily, mothers should ideally breastfeed their infants for at least four months. Experts recommended strict dietary rules in this regard. In order to reduce the risk of allergies in the child, breastfeeding women were told to avoid eggs, nuts, dairy products, or wheat products. Experts also advised against mixing baby food with cereals containing gluten. Fish as well as celery or carrots were to be avoided. 

New studies have turned these recommendations on their heads. They showed that children are more likely to tolerate food if they have come into contact with them in the womb or while breastfeeding [13]. Of course, this only applies if the child has not already developed an allergy!

FYI: If your baby has a food allergy, you as the mother must also avoid the corresponding food while breastfeeding.

How can you prevent an allergy?

The development of an allergy is a complex process that scientists still do not fully understand. Unfortunately, that means there are no air-tight tips you can apply to prevent allergies.

However, the medical community has given recommendations that can make an allergy a little less likely. They are aimed at “families at risk”, that is, families in which allergic diseases, neurodermatitis, or asthma already occur. Recommendations include [14]:

  • Mothers and children should not try to avoid allergens in their diet; the mother's consumption of fish can even have a protective effect.
  • Mothers should avoid tobacco smoke from pregnancy onwards
  • Pregnant women, women who are breastfeeding, and children should avoid coming into contact with mold.
  • Pets are not a problem, they may even reduce the risk of allergies—unless the child is already at high risk of developing allergies. In this case, avoid keeping a cat.
  • Try to expose yourself to as little car exhaust fumes as possible. 

Foods that cause allergies

170 Foods are considered allergens, but most reactions are triggered by a small minority of foods. The most common allergy triggers are cow's milk, eggs, peanuts, nuts, soy, wheat, fish, and shellfish [15, 16].

Foods that cause allergic reactions

Dairy milk allergies

Dairy allergies are the most common food allergies [17]. They usually develop in childhood and mostly disappear by the time kids go to school. People who are allergic to dairy react to all dairy products, including cheese, yogurt, butter, and cream, 92 percent are also allergic to goat's milk [18]. People with cow's milk reactions should also avoid products made from goat’s and sheep’s milk [19]. Important: An allergy to cow's milk is completely different from lactose intolerance.

Egg allergies

Allergies to chicken eggs are the second most common food allergy in childhood - after cow's milk. In this case, as well, most people tend to outgrow it by adulthood. [15].

FYI: Some foods have a lower potential to cause allergies if you cook them. Many allergy sufferers tolerate, for example, strongly heated milk or eggs used for baking much better. Peanuts, on the other hand, have an even higher allergenic potential if they have been roasted [20-22].

Nut allergies

When it comes to nut allergies, doctors differentiate between allergies to peanuts - which are actually legumes - and other nuts, which they call tree nuts. All nut allergies tend to trigger severe reactions, including anaphylactic shock [23,24].

Fish and shellfish allergies

A fish allergy often only shows up in adulthood. Those usually affected cannot tolerate all types of fish. Most fish allergy sufferers can easily eat shellfish and vice versa.

Shellfish allergies also usually develop during adulthood. Shellfish include all crustaceans including crabs and lobsters, mollusks (snails) including oysters, scallops and squids, and insects such as cockroaches and grasshoppers. Since house dust mites are shellfish, people who are allergic to shellfish often develop a dust allergy [18].

Wheat allergy

A wheat allergy most commonly develops in childhood and usually disappears before adulthood [7]. 20 percent of those allergic to wheat show cross-reactivity to other types of grain such as spelt and rye [18]. However, you should not avoid all grains if you suspect you might be allergic - this would restrict your diet far too much. If in doubt, it is better to carry out an allergy test. It is best to figure out what you can really tolerate by means of a provocation test. 

Important: a wheat allergy is not a celiac disease! As a wheat allergy sufferer, you can consume foods containing gluten as long as they do not contain wheat.

Spice allergies

Spices are found in all kinds of processed foods, cosmetics, and dental care products. However, they are not always marked on the packaging. This makes it difficult for allergy sufferers to avoid certain spices. Fortunately, spice allergies are relatively rare. The most common are allergies to cinnamon and garlic; reactions to black pepper and vanilla, for example, are less common [25].

Cross allergies

It is not the entire food that triggers an allergic reaction, but the allergens inside it. More specifically: certain proteins inside them. Sometimes several of these proteins are so similar that the body cannot tell them apart. In this case, cross-reactivity can occur: the body is sensitized to one allergen but also reacts to the other. This happens between foods - people who are allergic to peaches often also react to apples. It is also possible that a pollen allergy could lead to cross-reactivity with fruits, vegetables, and nuts. Even latex often triggers cross-allergies - with kiwis, bananas, and avocados.

Food and its possible cross allergies [15]:

 Allergic to: Cross-Reactive to: Risk
Dairy milk Goat’s milk 92%
Melons Watermelons, bananas, avocados 92%
Shrimp Crab, lobster 75%
Peaches Apples, plums, cherries, pears 55%
Pollen Apples, peaches, honeydew melons 55%
Salmon Swordfish, sole 50%
Walnuts Brazil nuts, cashews, hazelnuts 37%
Latex Kiwis, bananas, avocados 35%
Wheat Barley, rye 20%


Food allergy symptoms

There are a variety of symptoms that can indicate an allergy or intolerance. Some are easy and hardly noticeable, others are obvious and still, others are very dramatic, like an allergic shock. Food allergies do not only affect one’s mouth and gastrointestinal tract, one’s skin and the respiratory tract may also react [2, 6].

What are the symptoms of food allergies? 

Comparing: food sensitivity test vs allergy test

When comparing the merits of food sensitivity testing vs food allergy testing, the following symptoms are associated with allergic reactions and would belong to the latter group:

  • Skin inflammation (nettle rash)
  • Diarrhea, vomiting, and abdominal pain
  • A burning sensation in the mouth, swelling of the mucous membranes and tongue
  • Difficulty breathing, allergic asthma
  • A drop in blood pressure

Food Allergy Symptoms

Extreme case: allergic shock

The most severe form of allergic reaction is allergic shock, also known as anaphylactic shock. It mostly caused by insecticides, medication, and, especially in children, food. Once again, nuts, soy, shellfish, milk, and eggs are often the foods that cause shock.

In allergic shock, large amounts of histamine are released, which leads to a severe dilation of the blood vessels. This causes blood pressure to drop rapidly, causing dizziness, fainting, and, in the worst case, even death.

If the risk of shock is known, you should therefore react quickly if stronger allergy symptoms occur and call 911 immediately. Until the ambulance arrives, the person affected should be brought into the shock position, i.e. they should lie down with their legs raised. High-risk patients often also carry an emergency kit with them that contains an adrenaline pen (EpiPen). This emergency medication should ensure that the shock subsides [4, 5].

FYI: Depending on the severity of an allergy, even the smallest amounts of an allergen are sometimes enough to trigger an allergic shock - such as the nut residue on one’s partner's lips or traces of soy on certain foods [4, 5].

Factors that exacerbate allergies

Just because you have an allergy doesn't mean you automatically respond to the slightest sign of the allergen. The reaction threshold is what we call the specific amount of the allergen at which symptoms arise. Peanut allergy sufferers, for example, often have a very low reaction threshold; for them, a small crumb of peanut is enough to cause a furry tongue and a swollen throat.

Stress, sports, and infections can lower your reaction threshold. This makes it more likely that you will experience an allergic reaction.

During or immediately after exercise, the risk of an allergic reaction is increased. This phenomenon even has a name: exercise-induced anaphylaxis (EIA). If you eat food that you are allergic to right before exercising, you may get hives, feel itchy, or become drowsy. You should avoid your food allergens at least four to five hours before each exercise [26].

Studies have shown that stress can make allergy symptoms worse and more common. If you suffer from an allergy and are often stressed, it is worthwhile to specifically find time to relax. Relaxation techniques such as yoga, autogenic training, and progressive muscle relaxation can help.

Infections like the flu or cold can also make allergies worse. Elevated temperatures lead to increased blood circulation, which in turn allows more allergens to enter the blood. In the case of infections in the gastrointestinal tract, a further complication is that a large number of undigested proteins cross the mucous membrane. As a result, these proteins hit the sensitized immune system and are more likely to trigger an allergic reaction [27].

Alcohol has been mentioned among scientists as an allergy-enhancing factor. In some case studies, allergy symptoms worsened under the influence of alcohol, and the number of IgE antibodies is increased in alcoholics. There is however still no conclusive scientific evidence for this theory [27].

Food intolerance test vs allergy test

Do you suspect that you cannot tolerate certain foods because symptoms such as rashes, a furry tongue or gastrointestinal complaints keep coming up after eating? Then it could be time to test for a food allergy. There are four common health tests that can be used to detect allergies [28]:

  • Prick test
  • Blood test for IgE antibodies
  • Elimination diet
  • Oral provocation test

Skin prick and blood tests provide evidence of sensitization to certain allergens. Elimination diets and provocation tests are used to find out whether the sensitization is also an allergy with symptoms.

Prick tests

During a skin prick test, a doctor scratches allergens dissolved in liquid under your skin, usually on your forearm or back. If hives form at one point, this indicates that there is a sensitivity to the allergen introduced.

The prick test quickly provides initial results and is not painful - but can lead to severe itching [14].

Prick testing for allergies

IgE blood test for allergies: food allergy vs food sensitivity test

Laboratories can look for specific IgE antibodies in the blood. By "specific" we mean that the antibodies are targeted towards specific allergens.

You do not necessarily need to have this kind of IgE blood test to be carried out by a doctor. Home-tests such as the cerascreen® food reaction test allow you to take a blood sample yourself at home with a small prick in your finger. Then you would send your sample to a specialist diagnostic laboratory, which will examine your blood for IgE antibodies. The advantage of such a blood test is that one blood sample can be used to examine your body's reaction to many different foods. If specific antibodies are particularly common in your blood, you are sensitized to the associated IgE allergen.

This can be a clue - but it doesn't mean that you have an allergy! Some people have high levels of certain IgE antibodies, but no allergic reactions whatsoever. Only doctors can make a reliable allergy diagnosis. They combine the result of the IgE test with an anamnesis, i.e. inquiries about symptoms and the state of health. An allergy is only present if you are sensitized and you also experience symptoms when you eat the food in question. In some cases, the reactions to food allergies are relatively clear and dramatic. In others, the reactions are delayed or difficult to interpret. In such cases, doctors can recommend an elimination diet or perform a provocation test [14].

Elimination diet

An elimination diet allows you to remove foods from your menu that you suspect to be triggers. Such a diet is often the first measure that doctors prescribe if a skin prick test or blood test reveals a sensitization.

You shouldn't go on the elimination diet for longer than two to four weeks if you are investigating food allergies, and only for one food at a time. During this time, the first effects should already be noticeable if you are allergic to the food - changes are often noticeable very quickly [28].

Provocation test

The provocation test can definitively confirm a food allergy. This test must always be carried out by a doctor as there is a risk of allergic shock. The doctor will give you the food to be tested for and watch for any reactions. If there are no symptoms, there is no allergy.

Food allergy therapy

Food allergies cannot really be cured. Once you have it, you have to live with it - unless it disappears on its own. But on the basis of a reliable diagnosis, you can avoid the triggers, alleviate worse symptoms with medication, and prepare yourself for an anaphylactic shock with an emergency kit.

Avoid triggers and eat a balanced diet

It stands to reason that if you have a food allergy, you should no longer consume the food in question - not even in small quantities. If the allergy is accompanied by severe symptoms or if there is even a risk of allergic shock, you should carefully study the ingredients on the packaging. Highly processed foods in particular often contain ingredients that you might not necessarily expect.

The FDA obliges food manufacturers to label the 14 most common triggers of allergies and intolerances on their products: gluten-containing cereals, crustaceans, eggs, fish, peanuts, soybeans, dairy products, nuts, celery, mustard, sesame seeds, Sulfur dioxide and sulfites, lupins, and mollusks.

If you cannot tolerate just one or two foods, it is often easy to remove them from the menu and replace them. If you or your family has a lot of food allergies, things can quickly become complicated. In such a case, experts recommend nutritional advice. Here you will learn how to deal with allergens and still ensure a balanced diet.

Medication: antihistamines

Antihistamines, also known as anti-allergy tablets, weaken or cancel the effect of the messenger substance histamine. In this way, they can reduce allergic reactions all over the body. They are used for hay fever, but can also relieve minor symptoms of a food allergy, such as rashes, itchy palate, and nausea. The most common active ingredients are cetirizine and loratadine; they are available in pharmacies as drops and tablets without a prescription.

In the event of an allergic shock, however, antihistamines are usually not enough. This is why people with severe allergies to more dangerous allergens such as nuts and shellfish often have an emergency kit with them. The emergency kit contains an adrenaline pen that is injected into the thigh, glucocorticoids, and, for asthmatics, an inhaler.

At-home Food intolerance testing

Food intolerance

When considering whether to do a food allergy test vs a food intolerance test, it is important to know the difference. A food allergy is defined as a reaction of the immune system in which certain antibodies play a role, mostly IgE antibodies. This can be distinguished from food intolerances that cause non-immunological reactions to food. 

The intolerances include celiac disease (gluten sensitivity), intolerance to lactose, fructose, sorbitol, and histamine as well as IgG4-caused intolerance. According to experts, 15 to 20 percent of the world population is affected by some kind of intolerance, women more often than men [3,29]. The causes of intolerance are not always clear; possible factors are genetic predisposition and environmental influences [30].

Many people believe they have an intolerance to food - but in reality, this only applies to a fraction of them. In a UK survey, 20 percent of people believed there was a food intolerance in their household. Studies then showed, however, that only two percent of these 20 percent were affected by genuine intolerance [3].

Which symptoms are associated with intolerance?

In contrast to allergies, intolerances are usually expressed with a delay. If you eat something you cannot tolerate, it can take hours for the symptoms to settle. This often makes it difficult to recognize an intolerance and to find out which food is behind it.

The symptoms of intolerance are usually expressed in the gastrointestinal area. Unpleasant flatulence in particular is typical, but nausea, constipation, diarrhea, and vomiting can also occur. Other possible symptoms are:

  • Headaches and migraines
  • Wheezing and a runny nose
  • Rashes
  • Exhaustion

Common food intolerances

Scientists have a good understanding of a number of intolerances. We roughly know what is going on in the intestines and why those affected can no longer tolerate certain foods. The intolerances to lactose, fructose, sorbitol, histamine, and celiac disease have been well researched.

Lactose intolerances

Probably the most common intolerance to milk sugar is lactose intolerance. The milk sugar lactose is found in milk and many milk products. In the US, lactose intolerance affects up to 50 million people. In other regions, especially in Asia, it is even more common. In those affected, a certain enzyme that breaks down lactose is too rarely found in the intestine. The body cannot process this milk sugar properly, which leads to gas and stomach pain.

Fructose and sorbitol intolerance

People who are fructose intolerant cannot consume fructose. It is the substance that gives the fruit its sweetness but also occurs in some vegetables. A transport protein moves the fructose from the intestine into the blood. In the case of fructose intolerance, this transport protein does not function properly. Problems arise with the utilization of fructose. Symptoms range from flatulence and abdominal pain to fatigue and mood swings. Sorbitol intolerance takes place in a similar way - the intestines cannot process the sugar substitute sorbitol properly.

Gluten intolerance (celiac disease)

In the case of celiac disease, the adhesive protein, gluten, triggers an immune reaction that leads to inflammation in the intestinal mucous membrane and, above all, to gastrointestinal complaints and, in the long term, nutrient deficiency and secondary diseases such as osteoporosis and anemia. Gluten occurs in many types of grain, for example in wheat, spelt, and rye, and in numerous processed products. This is obviously very inconvenient for people who have to eat a completely gluten-free diet.

Histamine intolerance

Histamine intolerance is also known as a pseudoallergy. What it has in common with a food allergy is that the messenger substance histamine leads to symptoms such as reddened skin, flatulence, dizziness, and a runny nose. But while our immune cells release too much histamine in the case of an allergy, in the case of histamine intolerance, a certain enzyme that breaks down histamine from food is too rarely found in the intestines and blood. Histamine-rich foods such as red wine, long-aged cheese, and dried sausage then trigger the symptoms.

Symptoms of intolerance can also be psychosomatic. Your brain may, for example, associate traumatic memories with a particular food. As a result, your body could react with psychosomatic complaints when you consume the food again [3].

IgG4-caused incompatibilities

In addition to the IgE antibodies, the immune system has other tricks up its sleeve, including the IgG4 antibodies, the immunoglobulins G4. Our body also produces different IgG4 antibodies for all kinds of foods that we eat.

According to an alternative medicine theory, the production of certain IgG4 antibodies increases if we cannot tolerate certain foods. This could then lead to various immune and inflammatory reactions. An IgG4-mediated intolerance results. The reactions and the associated symptoms occur with a delay, sometimes hours or days after eating the food.

Testing IgG4 levels

The number of IgG4 antibodies can be determined with a blood test, for example using the cerascreen® food reaction test. Theoretically, a high number of antibodies that target a certain food could be an indication of an intolerance [29].

IgG4 intolerance tests are, however, the subject of debate: Researchers and specialist societies bemoan the fact that the IgG4 concentration is only an indication of the extent to which certain foods have been eaten. It doesn’t tell us anything about possible allergies - instead, it indicates an immune tolerance. So far, there has not been a large-scale study that has examined the relationship between IgG4 levels and food reactions [3, 29].

Intolerances to histamine, lactose, fructose, and sorbitol as well as celiac disease cannot be determined by an IgG4 intolerance test. Different blood or breath tests are necessary to find out about these conditions.

What do my IgG4 test results mean?

An increased number of IgG4 antibodies does not mean that you cannot tolerate a certain kind of food. You can, however, omit the foods identified in the test from your diet and observe whether your symptoms improve. If the test shows you a clear reaction to a food, remove it from your menu for two weeks. If your symptoms improve, as a result, this is an indication that there may be an intolerance involved. You can then eliminate the food for the next six months. After that, try to slowly bring it back into your diet.

An alternative is the rotation diet. With this diet, you can eliminate several potential intolerance triggers. To do this, you eat the foods to which you have reacted in the IgG4 test only every four days. In the meantime, your bowels can recover. This rotation can already lead to a significant reduction in the symptoms.

Food reactions: A brief summary

What is a food allergy?

Food allergies occur when our immune system fights harmless proteins (which we call allergens) that are in the food. The mast cells of our immune system release histamines, which cause inflammation and can cause discomfort all over the body.

What are the symptoms of a food allergy?

A food allergy can result in gastrointestinal complaints, an itchy palate, and a furry tongue. Redness, itching, and rashes on the skin as well as respiratory problems and even asthma are also common. In rare cases, a patient’s blood pressure can drop and anaphylactic shock can occur.

Which foods trigger an allergy?

Theoretically, many foods can trigger allergies. In practice, however, a few foods are responsible for more than 90 percent of allergies. These include dairy products, eggs, peanuts, nuts, soy, wheat, fish, and shellfish.

How do I recognize a food allergy?

If you suspect a food allergy, you can do a blood test, among other things. The test determines the number of IgE antibodies in the blood. If your IgE level is elevated, you may be experiencing a sensitization to the food associated with the antibody, in which case you should avoid the food for a while to see if your symptoms go away.

What is food intolerance?

When it comes to intolerances, symptoms are not caused by immune reactions as in an allergy. Instead, the intestines often have problems processing certain components of food, for example, gluten, histamine, lactose, or fructose.

What are the symptoms of food intolerance?

In contrast to a food allergy, an intolerance is often not immediately apparent. Symptoms sometimes take hours or days to appear. Typical symptoms are gastrointestinal complaints, especially gas, headaches and migraines, a runny nose, rashes, and fatigue.

What is IgG4-triggered food intolerance?

Theories suggest that the immune system's IgG4 antibodies can provide an indication of food intolerance. With the help of the IgG4 values from a blood sample, you can try out elimination and rotation diets, which can provide more information about intolerances, which can in turn help reduce symptoms.

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