More and more people are experiencing adverse reactions to food but not everyone who experiences them will be diagnosed with an allergy.

The words ‘allergy’ and ‘intolerance’ are often mistakenly interchanged when referring to a reaction to food; when in reality food allergies are much rarer than food intolerances.

Some of the symptoms might initially seem similar, however there are some important differences.

Food allergy

An allergic reaction to food occurs when the body’s immune system views a food substance as a threat, much in the same way as it would view an infection.

In order to tackle the presumed threat the body may react in a number of ways.

In immediate allergic reactions the body releases immunoglobulin E (IgE) antibodies that trigger a release of histamine. The presence of this chemical can cause numerous allergic symptoms such as breathing difficulties, skin rash, swelling, diarrhoea and vomiting.

The body can also produce non-IgE-mediated responses that tend to be less severe and often delayed. A white blood cell known as a T-cell tends to be behind the response which can lead to eczema, skin problems and digestive difficulties.

A severe and systemic reaction to foods is known as anaphylaxis and can lead to death if not treated efficiently.

Food intolerance

An intolerance is caused by an inability to process a particular food substance which often irritates the digestive system.

The reaction does not trigger an immune response and tends to cause a different set of symptoms.

The symptoms may not appear immediately but they can last from several hours or several days. They can vary greatly from bowel and skin problems through to a general feeling of fatigue, headaches and bloating.

Food intolerances can be instigated by a number of factors including enzyme deficiency, irregular food intake, a diet high in refined foods or fat, poor nutritional choices or not enough fibre.

Living with a food intolerance can be difficult especially if you are unsure what is causing your reaction.

Some foods produce natural chemicals that can have a negative effect on some people. One example of this might be amines found in certain cheeses.

Living with a food intolerance does not necessarily mean you will have a negative reaction to the food every time you eat it. It may be that you need to consume over a certain amount before you notice any symptoms.

However, depending on the severity of the condition you may wish to alter your diet accordingly. Your doctor can discuss this with you to ensure that you are not missing out on vital nutrients.

The subject of food intolerance is still an uncertain one for experts, as while symptoms may be present to the person experiencing them, the body may not produce any medical abnormalities upon examination.

Lactose intolerance

An intolerance to lactose is one of the most common types of food intolerance. It occurs when the body lacks the enzyme needed to break down the natural sugar found in dairy.

In such cases, lactose cannot be absorbed into the bloodstream, which results in it being transferred to the large intestine where it ferments.

This process can lead to uncomfortable symptoms such as abdominal pain, sickness, diarrhoea and flatulence.

It is thought that your genetic makeup can determine how likely you are to develop lactose intolerance. You can be born with a lactase deficiency or you can develop it at any stage in your life.

The severity of the condition can vary greatly from person to person and some lactose intolerants might be able to avoid symptoms if they limit their intake to one glass of milk per day, whereas others might react badly to a small amount of lactose.

Lactose-free products are available to buy from many supermarkets and those with the condition are usually able to enjoy a relatively unaffected diet.

Coeliac disease

Gluten is a protein found in various foodstuffs including wheat, barley and rye.

Coeliac UK states that one person out of 100 people is not able to digest gluten.

Those who cannot process gluten may be given a diagnosis of coeliac disease or non-coeliac gluten sensitivity. You can use a home gluten sensitivity test to find out whether the antibody IgA tTG is present in your blood, a positive result may indicate coeliac disease. 

It is important to note that coeliac disease is neither an intolerance nor an allergy but is in fact an autoimmune disease.

If gluten is consumed by a coeliac the body reacts by attacking itself and potentially damaging the small intestine’s lining. The resulting damage can alter the structure of the intestine so that it is not able to absorb nutrients efficiently.

Non-coeliac gluten sensitivity may produce similar symptoms but it does not result in damage to the intestines.

Following a gluten-free diet is currently the only treatment for the condition. It can give your gut time to heal and eventually relieve symptoms.


Food additives such as preservatives, sweeteners and colourings can cause adverse reactions in a small percentage of people. The majority of those diagnosed are thought to be intolerance-based rather than allergic.

It can be difficult to achieve a diagnosis when it comes to food additives as there are no specific tests for this type of intolerance.

Drug allergy and drug intolerance

You might not be able to tolerate the use of a particular drug due to other underlying health conditions, known as contraindications.

Another reason may be due to potential interactions with other medicines that you are taking or have recently taken. In these instances the doctor or healthcare professional will assess the risk that the drug poses and the chances of a reaction occurring.

Experiencing side effects when taking medication is normal and the majority are not classified as allergic reactions. However, it is possible to have actual allergic reactions to certain medications. Penicillin and contrast injections for x-rays can provoke such reactions.


Many types of alcoholic beverages contain varying levels of histamine, sulphites, additives and yeasts, which have the potential to cause a negative response.

However, true alcohol allergies are extremely rare.

Much like the other allergies listed above, an alcohol allergy causes the body to release IgE antibodies into the system. In turn this reaction can cause unpleasant symptoms such as difficulty breathing, rashes and collapse. It is also possible for alcohol to cause anaphylaxis.

Those who are intolerant to alcohol may notice symptoms such as skin flushing and nasal stuffiness. This type of response can be triggered when the body is unable to effectively break down alcohol molecules.

Some people experience a noticeable response to all forms of alcohol; whereas others only notice symptoms if they drink certain types. If you have either an alcohol allergy or intolerance you will be advised to avoid it.

Page last reviewed:  22/02/2021