Food Allergy Explained

gingerbread man When someone has a food allergy, their immune system reacts rapidly to a particular food as if it isn't safe. In theory, allergy can be caused by any food, although there are eight particular foods that cause most cases. A classic (or Type I) allergy can cause reactions varying in severity from skin rashes, to a life threatening allergic reaction known as anaphylaxis (life-threatening respiratory distress).

Food intolerance involves slower reactions and either does not involve the immune system or if it does the immune reaction proceeds much more slowly. Intolerance is generally not a life-threatening condition. If someone eats a food they are intolerant to, this can make them feel ill or affect their long-term health. There are no 'rules' when it comes to food intolerance - different foods affect different people in different ways. Often, it is extremely difficult and time consuming to pinpoint which food is making someone feel unwell. Food intolerance has been linked to many different conditions, including IBS, migraines, asthma, eczema and chronic fatigue.

Lactose intolerance is one example of a food intolerance. A person with lactose intolerance lacks an enzyme that is needed to digest milk sugar. When the person eats milk products, symptoms such as gas, bloating, and abdominal pain may occur.

Masked allergy


 A masked allergy is one that results in a delayed reaction to a particular food or allergen. It may also be referred to as an intolerance rather than an allergy. Some definitions of intolerance (masked allergy) claim no involvement of the immune system. However it is increasingly recognised that some of the affects of food intolerance involve a slow allergic reaction to certain foods involving the secretion of increased amounts of specific IgG antibodies by the immune system into the blood. This is known as a Type 3 (immune complex) allergic reaction. Conventionally type 3 reactions involve IgA and IgM antibodies, however in the context of food intolerance it is IgG antibodies that are assumed responsible for the effects.

Conventional allergy

An obvious allergy is one that results in a rapid response by the immune system to a  food that the body mistakenly believes is harmful. The immune system then creates specific antibodies to the food, and the next time the individual eats that food, the immune system releases chemicals, including histamine, heparin, kinins and various prostaglandins, in order to protect the body. These chemicals trigger a cascade of allergic symptoms that can affect the respiratory system, gastrointestinal tract, skin, or cardiovascular system. This is known as a type 1 (anaphylactic) allergic reaction.

Chemical contaminants in food which can cause an allergy/intolerance

A large number of chemicals are in our food and drinks. Some are naturally occurring, such as caffeine and aflatoxins, while others are added in, such as preservatives, flavour enhancers and colours.

Naturally occuring substances in food - can cause allergic reactions

  • Caffeine for instance, which for some people causes insomnia, palpitations, headaches, gastrointestinal disturbances as well as hyperventilation, breathlessness and fatigue.
  • Aflatoxins in peanuts can cause life threatening anaphylaxis.

Food additives - are a common direct cause of allergies

  • Preservatives such as sulphites can trigger asthma. Benzoic acid may cause asthma and urticaria (an itchy rash), while some antioxidants can trigger asthma, urticaria and rhinitis.
  • Flavour enhancers such as monosodium glutamate can cause headaches and tightness of the chest, neck and face, while aspartame can trigger urticaria and swelling.
  • Colourings such as tartrazine can trigger asthma, urticaria and generalized allergic reactions.

Antibiotics and hormones - indirectly increase reactions to foods.

  • Antibiotics in children have been linked to an increased likelihood of developing allergies. This may be due to their effects on the developing immune system.
  • Hormones, which can act as very potent chemicals, could also affect the immune system and result in more allergies.
  • Pesticides, herbicides, histamine and heavy metals – if present in our foods can also cause allergy or intolerance.

How to avoid food contaminants

There are several ways of reducing the risk of consuming contaminated foods, which as well as increasing the risk of allergy and intolerance can affect health in other ways as well.

  • Eat organic food – which are grown without the use of pesticides, herbicides, antibiotics and certain additives as well as without genetic modification. Trans fats are also discouraged in organic produce. The accreditation body for any organic product should be noted as some are more rigorous than others. The Soil Association is one of the best. Many pesticides contain heavy metals, which can also cause many health problems on their own.
  • Avoid eating excessive amounts of marine species – especially those higher up the food chain such as carnivorous fish, sea mammals and sea birds. PCBs and dioxins accumulate in the fatty tissues of animals, becoming more concentrated higher up the food chain. Exposure is linked with hormonal disruption and increased risk of certain cancers.
  • Avoid eating too much offal – as these organs, while containing concentrated amounts of valuable micronutrients also contain toxin in concentrated amounts.
  • Avoid foods wrapped in plastic – especially Clingfilm, as organochlorines, such as PCBs can leach out if the plastics are heated or become damp. 
  • Use glass or earthenware containers – for foods where possible, and in the case of fat containing foods, keep them out of the light as this helps prevent the creation of trans fats.
  • Use filtered or spring water – if there is a concern about the quality of the local tap water. Tap water can contain heavy metals from piping, industrial residues, such as nitrates and chlorine and fluorine used to sterilize water and prevent tooth decay. All these chemicals can affect health.
  • Avoid food additives – which are present in most processed foods. Some food additives are harmless, but others are well known for their allergic potential. A good site for food additive safety information can be found at

The most common causes of food allergy/intolerance

In theory, any food can cause a food allergy. But in fact just a handful of foods are to blame for 90% of allergic reactions to food in the UK. These foods are known as the 'big eight'. They are: milk, eggs, peanuts, nuts (including Brazil nuts, hazelnuts, almonds and walnuts), fish, shellfish (including mussels, crab and shrimps), soya and wheat.

In children, the most common allergic reactions to food are to milk, eggs, peanuts, nuts, soya and wheat. Usually children grow out of most types of food allergy in early childhood. Especially allergies to milk or soy products. In adults, most allergic reactions are to peanuts, nuts, fish, shellfish and wheat.

There are many more foods that are associated with food intolerance. The most common food intolerances, in order of frequency are milk, eggs, nuts, fish/shellfish, wheat/flour, chocolate, artificial colours, pork/bacon, chicken, tomato, soft fruit, cheese and yeast. Other foods commonly associated with food intolerance are soya and corn.

It can be seen that the most common foods involved in food intolerance are meats, dairy and bakery/bread related products. However a large number of processed foods contain milk, soya and wheat proteins as well as yeast and this can make avoiding problems foods quite a challenge.

It can also be seen that the culprits for food intolerance are often culprits for type 1 food allergies also.

The digestive system and food allergy/intolerance

The digestive system provides a protective barrier of epithelial cells that line the gastro-intestinal tract. This barrier, along with the enzymes that break down potentially troublesome protein molecules plays an important role in determining the likelihood of allergy/intolerance reactions.

The digestive barrier

If the integrity of the mucosal lining of the gut becomes compromised, as in leaky gut syndrome, then undigested foreign particles (normally peptides) are increasingly able to penetrate into the fluid compartments of the body. Inside the body the foreign peptides come into contact  with cells of the immune system which may react if they recognise the peptide as an invader.

Efficiency of digestion

If the enzymes that break down proteins within the gastro-intestinal tract are deficient, then more undigested peptides may reach the mucosal lining of the intestines, allowing for more absorption of these peptides and an increased likelihood of immune reaction. Reduced digestive efficiency could also result from low stomach acid and chronic stress or infection.

The immune system and allergies

In a classic Type A food allergy, the immune system is triggered by the presence of antigens in the foods that we eat. Normally these antigens form part of proteins. The antigens are recognized by surface receptors on B lymphocytes, which then produce antibodies known as Immunoglobulin type E -  IgE. The IgE molecules attach to mast cells, which are found in the connective tissue beneath most epidermal layers in the body, typically in the nose, ears, mouth, throat, lungs, skin and gastrointestinal tract. The mast cells then release inflammatory chemicals, including histamine, that cause blood vessels to dilate and become leaky, allowing immune cells and fluid to leak into the interstitial spaces causing redness and swelling.

In a type 3 (delayed) food allergy it is thought that other components of the immune system, namely Immunoglobulin type G - IgG antibodies, are produced. In addition secretory immunoglobulin A – sIgA, found on most mucosal surfaces of the body, is often found to be deficient in people with food intolerances. IgA prevents antigens from binding to mucosal surfaces, limiting their entry into the body. Deficiency of IgA is also associated with increased gut permeability.

The endocrine system and food allergies

The endocrine system includes various hormones which play a role in determining the strength of an inflammatory response during allergy. The most important hormones are histamine, cortisol and epinephrine.

  • Histamine is the key chemical involved in creating an inflammatory response by causing vasodilation of blood vessels, making capillary walls leaky and causing smooth muscles to contract in the lungs. It also stimulates increased mucus production. It is synthesized from the amino acid histidine by mast cells, which are found in connective tissue beneath most epithelial surfaces.
  • Cortisol is secreted by the adrenal glands in response to allergic reactions. Cortisol dampens down the inflammatory response by neutralising histamine. If the adrenal glands are not working properly then allergic reactions may worsen.
  • Epinephrine is also produced by the adrenal glands and counters all the effects of anaphylactic shock in a type I allergic reaction. In serious cases the body can’t produce enough and it is administered intravenously to resuscitate victims of bee stings, snake bites etc.

There is some evidence that people can be allergic to hormones themselves. This is considered to especially affect women whose levels of hormones fluctuate throughout the menstrual cycle. This aspect of allergy is however not yet part of the mainstream of allergy science.

The most common causes of food allergy

The most common causes that predispose a person to food allergy include the following:

  • Absence of  breast milk in infancy. Consumption of breast milk not only protects a baby from infection, due to bacteriostatic substances such as the protein, lactoferrin, it also helps establish a healthy population of gut bacteria. A healthy population of gut bacteria is associated with reduced incidence of allergies.
  • Being born prematurely. Premature birth exposes the newborn to external microbes and molecules, which it wouldn’t otherwise have been. However recent peer reviewed studies by the American Academy of Allergy do not suggest it is a significant factor in the likelihood of developing childhood allergies. This suggests that exposure to certain allergens in early life may actually be helpful. It could be a more complicated picture than we think.
  • Having a leaky gut. If gut wall permeability increases then more peptide fragments can come into contact with immune cells inside the body. As a result, the chance of the immune system developing hypersensitivity reactions to certain proteins in foodstuffs is increased. This is especially so in the case of infants whose digestive tract in the first 6 months will not have fully developed.
  • Various drugs. Many drugs have an immuno-suppressive effect. These include HIV and AIDS drugs, drugs used in chemotherapy, alcohol and the non-steroidal anti-inflammatory drugs – NSAIDs.

Some of the conditions provoked by food allergy

  • Allergic Rhinitis or hay fever.
  • Anaphylaxis – sudden constriction of breathing passages and drop in blood pressure. Potentially fatal.
  • Arthritis – inflammation of the joints.
  • Asthma – inflammation of the bronchial tubes.
  • Conjunctivitis - eye inflammation.
  • Dermatitis including eczema and contact dermatitis.
  • Irritable bowel – non-inflammatory bowel disorder.
  • Otitis media – middle ear inflammation.
  • Peptic ulcers – symptoms can worsen.
  • Sinusitis – inflammation of the nasal sinuses.
  • Urticaria or hives – red itchy weals on the skin.

Treatment of delayed-onset food allergy

Delayed onset food allergy is not always easy to treat however the following methods can be effective.

  • An elimination diet followed by careful re-introduction of suspected foodstuffs one at a time. If foodstuffs are identified that cause problems then these can be eliminated from the diet. Appropriate dietary adjustments can then be made to ensure that the allergy sufferer still maintains a balanced diet containing all the essential nutrients and micronutrients in ample amounts. This kind of diet requires attention to detail as many food substances are present in multiple sources. For instance gluten found in bread is also used throughout the baking industry and is also used as a thickening agent in soups and other processed foods.
  • Avoidance of drugs that have an immuno-suppressive effect such as NSAIDs, smoking and alcohol.
  • Prioritise the treatment and recovery from low level infections that stress the body and can exacerbate food intolerance symptoms. For instance echinacea could be used to shorten the duration of colds.
  • It may be worth including supplements in the diet if deficiency is either suspected or proved. Also some micronutrients could be beneficial in improving the condition. For instance the minerals zinc, copper and selenium all play a role in immune function, while the amino acids glutamine (essential for energy production in lymphocytes and macrophages) and to a lesser extent tyrosine can also boost immune health. (See below).

Nutrients for someone with multiple food allergies

Someone with multiple food allergies should adopt an hypoallergenic diet. Added to this would be various nutrients, from both foods and supplements, intended to reduce the persons susceptibility to allergy. Such nutrients include:

  • Glutamine – which can be found in fermented foods such as miso and yoghurts as well as in supplement form stimulates the immune system. It does this in a number of ways including:

    • Reducing gut permeability in the colon. (Enterocytes use glutamine as a respiratory fuel).

    • Maintaining secretory IgA in the gut, which prevents pathogens attaching to gut walls.

    • Supporting production of anti-inflammatory cytokines such as IL-2 and interferon gamma.

    • Enhancing phagocytosis by neutrophils and monocytes.

    • Relieving oxidative stress by boosting production of the body’s antioxidant enzyme, glutathione in the liver.

  • Tyrosine – affects a number of neurotransmitters produced by the elements of the endocrine system. It may also, in conjunction with vitamin B3 and B6, affect allergic reactions by damping down symptoms of urticaria and hay fever.

  • ACE vitamins – Vitamins C can act in ways similar to antihistamines, reducing allergy symptoms, while vitamin E can also reduce symptoms.

  • Immune enhancing minerals – Zinc, selenium and copper can also help allergic food reactions by modulating the immune system. For instance zinc helps create prostaglandins, some of which have a stabilising effect on the immune system.

  • Water – to maintain hydration levels. This ensures that the mucosal surfaces of the body that come into contact with allergens remain lubricated and are able to function most effectively.

  • Enzymes – eaten soon after a meal to enhance the breakdown of food particles in the gut. Would be effective only in cases where enzyme insufficiency was present such as with lactose intolerance or cystic fibrosis.