Last partial update: June 2019 - Please read disclaimer before proceeding
Allergic disease
The rates of both asthma and allergic rhinitis increased significantly in Australia in the 1980s and 1990s. The cause of this increase is unknown but suspects include increasing pollution, reduced ventilation in modern homes and changes in diet causing increased exposure to food allergens.
Food allergies
Many people have adverse reactions to foods but most of these are not true allergic reactions (i.e. immune system mediated reactions). Having said this, food allergy has increased dramatically in western countries over the past 20 years and unfortunately the cause of this increase is not clear. This increase has resulted in up to 10% of one year old children having a true food allergy (IgE mediated) on testing.
Allergic food reactions usually occur with the first exposure to the food, which is often before the age of two. Up to 4% of the population have an allergy to at least one food, with most of these being mild in extent. For example, symptomatic peanut allergy occurs in about 1% of children while severe anaphylsctic / life-threatening reactions only occur in about 10% of this group (i.e. about 0.1% of all children). It is important to note that significantly more people have a positive allergy test for a particular food (i.e. they are sensitised to the food) but have no symptoms. In the case of peanut allergy, about 3% of all children test positive for peanut allergy but, as stated above, only 1% have symptoms.
Most food allergies can be divided into three groups; IgE mediated, non-IgE mediated and a mixture of both.
1. IgE mediated: IgE mediated reactions usually occur within 5 to 10 minutes after ingestion (but can be up to a few hours). Only small amounts of the food are required to produce the reaction. Common reactions include skin symptoms such as itching, redness and swelling and reactions in the mucosa of the mouth and throat. About 4% of the general population have an IgE mediated food allergy of some sort but the rate is much higher in people who have eczema (about 33%) and significantly higher in people with asthma. Peanut allergy is an example of an IgE mediated food allergy.
Anaphylactic reactions are a severe form of this type of IgE mediated allergic response where symptoms develop quickly soon after the food is eaten, and is associated with cardiovascular and respiratory (breathing) systoms that can be fatal. The occurence of these severe reactions has also increased significantly in recent years.
2. Non-IgE mediated (cell mediated): Non-IgE mediated reactions cause delayed symptoms, usually occuring more than 24 hours after ingestion of the food. Usually larger amounts of the food are required to produce the reaction. An example is food protein enteropathy (a food protein allergic reactions in the bowel). Thus, symptoms are not asociated with eating the problem food. Symptoms can also be vague and thus the condition is often mistaken for other illnesses.
3. Mixed reactions due to both IgE and non-IgE mechanisms: Atopic resposes (e.g. eczema) can be IgE mediated or non-IgE mediated or, as in eczema, a combination of both. The symptoms are chronic in nature and delayed and the patient thus has difficulty associating them with intake of the causal food. Allergy skin testing can often usueful in identifying allergens in these people.
Symptoms of food allergy |
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Skin |
Gastrointestinal |
Respiratory |
Cardiovascular |
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Acute (IgE mediated) |
Urticaria, itch, redness | Tongue swelling, vomiting, diarrhoea, abdominal pain | Runny nose, cough, wheeze, stridor | Pallor, low blood pressure, fast &/or irregular pulse. |
Chronic (non-IgE mediated) |
Vomiting, diarrhoea, reflux, failure to thrive, haematochezia, abdominal distension | |||
Mixed (IgE & non-IgE mediated) |
Eczema, recurrent urticaria / angioedema | Difficulty swallowing, reflux symptoms, abdominal pain, failure to thrive. | Recurrent wheeze / asthma (asthma is rarely caused by an isolated food allergy and other factors are also usually present) | |
Non-allergic food reactions
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Common causes of food allergy
Ninety per cent of food allergies that occur within a couple of hours of exposure involve one of the eight most common causal foods; cows milk, hens egg, soy, peanuts, tree nuts (and seeds), wheat, fish and shellfish. Children often develop tolerance to cows milk, egg, soy and wheat by school age, whereas allergies to nuts and shellfish are more likely to be life-long.
Symptoms of food allergies
Symptoms include acute skin rashes such as hives (especially around the mouth), diarrhea, irritability, vomiting and wheezing, and are usually consistently related to exposure to the food. Poor weight gain is a longer-term symptom. Atopic dermatitis (eczema) and asthma may also be present.
Delayed-onset reactions (occurring within several hours to days after ingestion) do occur and are often difficult to diagnose. They usually do not give a positive skin prick test and elimination or challenge protocols are needed to make a diagnosis. Symptoms of delayed reactions include atopic dermatitis, infantile colic, gastro-oesophageal reflux, oesophagitis, diarrhoea and constipation.
Cow's milk allaergy: Cow’s milk allergy is a reaction to the proteins in cow's milk and occurs in about 2% to 5% of infants, usually starting in the first few months of life. Most cases resolve by school age. Its onset should start within four weeks following the introduction of cow’s milk into the infant’s diet. Symptoms may occur soon after the ingestion of cow’s milk (e.g. rash or wheeze) or it may present with delayed onset symptoms. It normally responds to the replacement of cow’s milk with either soy-based formulas or hypoallergic formulas. Heating cow’s milk can also reduce symptoms by destroying most (but not all) of the proteins in the cow’s milk that are responsible for the allergic problem. It can be either IgE or non-IgE mediated or a combination of both.
- IgE mediated: Occurs after first or second exposure to cows milk and thus almost always starts in infants. As with all IgE mediated allergic reactions, symptoms come on abruptly soon after ingesting even a small amount of cow's milk and can be severe / life threatening.
- Non-IgE mediated: This is a group of conditions with symptoms dependant on where the allergy to the milk protein occurs. The reaction can occur in the oesophagus, causing relux; in various sites in the bowel causing vomiting, diarrhoea, bloating, poor feeding / food refusal, failure to thrive and anaemia, blood in the faeces. It can vary in severity and milder cases can present at any time in life. However, most cases present in infants soon after cows milk is introduced.
Peanut allergy: Peanut allergies seem to be increasingly common. It is important to actually document a suspected case by skin-prick testing as many foods contain peanut extracts e.g. chocolate and icecream. With regard to peanut allergy, recent evidece suggests that delaying exposure to peanuts in the diet actually inceases the incidence of peanut allergy while introducing after solids have been successfully introduced (well before 12 months) is protective. Most peanut allergy seems to be present by 12 months so if early introduction is going o be beneficial, then peanut needs to be given well before this time.) This has changed dietary food recommendations for infants (see below).
Correct diagnosis (preferably by a specialist allergist) is important to avoid unnecessary dietary restrictions
In all food allergies, the best treatment is to correctly identify the food concerned and avoid its consumption. Because this involves the inconvenience of long-term dietary manipulation, it is important to make the diagnosis correctly. Many children are unnecessarily placed on inconvenient (and potentially harmful) restrictive diets; especially children with chronic eczema. Thus, a diagnosis of food allergy is best made by a specialist in allergies. (A GP will know one.)
It is important to understand that a positive food allergy test, either skin prick or blood, is not sufficient to diagnose a food allergy. Diagnosis also requires the food in question to be shown to cause symptoms in the individual. (Many people have postive tests but no symptoms.)
Food avoidance and allergy prevention
in the past, parents of infants at high risk of developing allergic disease (i.e. those with a family history of allergic disease) have been advised to adopt dietary manipulation (usually food avoidance) in the hope that it will prevent food allergies in their children. These measures involved either the pregnant or breast feeding mother or the infant. Evidence has proven that this advice has been incorrect and now all infants are treated the same with regard to the introduction of solids.
Introducing solids to infants - Normal solids and allergic solids
There is now general aggreement that the best way to avoid allergies in all children, whether they are at high or low risk of allergy, is to do the following
- Introduce solids at around six months but not before four months. This is the NHMRC recommendation. The Australian Society of Clinical Immunology recommend between 4 and 6 months.) Foods that commonly cause food allergies such as eggs and peanuts should be introduced gradually starting with very small amounts. For example, smearing a small amount of peanut butter on the gums of a child. Food should always be given in the mouth, not on the skin.
- Introduce allergenic solids once normal solids have been successfully introduced at around the same time (6 months ) and well before 12 months. These foods include egg (best introduced cooked, such as boiled egg), peanut pastes, wheat products, and dairy. This has been shown to be the best way to redice the risk of developing allergies to these foods. (Introducing eggs between 4 and 6 months reduces the incidence of egg allergy by about 40%.) This is a significant change to previous advice and applies to both high risk and low risk infants. In fact, high risk infants are the ones who are most likely to benefit from this earlier introduction of allergic solids as they were the ones who are most likely to avoid developing allergic disease. It is hoped that this approach to the introduction of allergic foods will halve the rate of food allergy in the community.
- Obviously, if you are worried that your baby has had a reaction to a particular food, do not give that food again and seek the advice of your doctor.
Infant formulas
- There is no evidence that hydrolysed milk formulas offer any benefit with regard to reducing the incidence of allergic disease in either high-rish or low-risk infants and their use is not recommended. A standard cow's milk formula is the preferered option for all infants.
- Soy formula is generally not recommended as a replacement where the mother cannot or chooses not to breastfeed.
Maternal restrictions in pregnancy
- Studies have not shown dietary restrictions (including peanuts, cow's milk and eggs) during pregnancy to be effective and thus should not be recommended. (in the past the American Academy of Pediatrics did recommend avoiding peanuts.)
Maternal food restrictions while breast feeding
- Generally, studies have not shown dietary manipulation in lactating women to be of benefit in preventing childhood allergic disease, especially in children over the age of two years.
- In breast-fed children who already have allergic symptoms due to a particular food, reduction in exposure can be beneficial and restricting maternal intake of the food while breastfeeding may be of benefit, depending on the individual situation. (Mothers should discuss this with their doctor before restricting their intake.)
- The consumption of prebiotic or probiotic supplements by mothers during pregnancy or while breastfeeding has not been shown to be beneficial. (This is also the case for infants.)
Diagnosis and Management of food allergies
The diagnosis and management of food allegies is beyond the scope of this prevention oriented health web site.
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Penicillin / antibiotic allergy.
About 25% of adults say that they have an allergy to an antibiotic, but in probably half of these people this is not true. People are incorrectly labeled as having an antibiotic allergy primarily because either;
- a minor side effect associated with taking the medication, such as some nausea, was incorrectly labelled as an allergic reaction, or
- a symptom caused by the infection being treated was incorrectly attributed to the antibiotic. This most commonly occurs when children get a viral rash at the same time as they are prescribed the drug and the rash is incorrectly attributed to the antibiotic. This is often the case with penicillin.
Such incorrect labeling should be avoided as it is carried throughout life and means that, when the person requires an antibiotic, the choices are restricted and perhaps the best choice is not used. It also may mean that antibiotics usually reserved for resistant infectiosn are used more often and this may increase bacterial resistance to these drugs in general.
Interestingly, an allergy to a type of antibiotic, such as penicillin, is not as simple yes or no concept. Sometimes, the alleggyis to th particular e type of penicillin taken (there are several types) and the person is not allergic to all types of penicillin.
The implication here is that, when you are asked whether you are allergic to a medication, rather than saying just yes or no, it is best to give a description of what actually happened when you took the drug. And if you were just told by a parent that you are allergic to penicillin and can't remember the circumstances, you should say that. This will allow your doctor to assess whether you are truly allergic.
Anaphylactic reactions
Anaphylactic reactions are severe allergic reactions that can lead to death. The onset of symptoms is usually rapid, within seconds or minutes of exposure, with symptoms including itch, tingling, hives, restlessness, faintness, palpitations, coughing, wheezing, change in voice, lump in the throat or difficulty breathing.
This is followed by swelling in different parts of the body (termed angioedema) that may cause airway obstruction, swollen tongue, face and lips, and hive-like skin rashes. Lower blood pressure and high pulse rate (shock) may also occur.
Common causes include drugs (e.g. penicillin), foods (especially peanuts, which cause about 90 per cent of life-threatening food reactions) and stings (bees and wasps). Injected allergens (e.g. drugs or stings) present the greatest problem usually.
Deaths from anaphylactic reactions are increasing and mostly occur in adolescents / young adults (due to food and insect bites, esp bees) and adults (mostly due to reactions to medications). Also, people with asthma have a greater risk of anaphylaxis and of dying from anaphylaxis.
Deaths from anaphylactic reactions to foods in children (including peanuts) are quite rare, with about two deaths occurring every ten years. Peanut allergy is increasing world-wide but the number of people with an allergy to peanuts is still small; about two per cent in Australia. The cause of the increase is not known.
Seeing a specialist: It is important to realise that anaphylactic reactions often occur in people who have previously had only mild reactions. Thus, anyone who has had an allergic reaction should have the cause accurately diagnosed by an allergy specialist and have a plan in place in case a severe reaction occurs in the future. Adolescents often delay seeking treatment and this increases the risk of death.
Epipen: An Epipen that is a pen-shaped instrument containing adrenalin that can be administered (injected) by the patient in the event that an anaphylactic reaction occurs. It can be a lifesaver in these situations. An Epipen should always be carried by a person who has had a previous serious allergic reaction, either an anaphylactic-like event or a significant airway restriction. (About one in 150 school children have had at least one such reaction.) They should not be given to people who have had mild allergic reactions ‘just in case’. They are available in both adult and child doses. The pen should not be stored away in a schoollocker etc as it can be needed urgently and people can collapse while trying to get to the pen.
Asthma
See section on respiratory disease
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