From an allergological standpoint, cow’s milk is one of the most common allergy triggers in infants and toddlers. It is estimated that more than two per cent of children in industrialised countries are allergic to cow’s milk. The allergy is not as common in adulthood.
In a self-report survey, 2.3 per cent of Europeans claimed to have a milk allergy. However, according to the figures from 42 studies in which the patients underwent a medical diagnostic procedure, significantly fewer people were allergic. Provocation testing revealed that only 0.6 per cent of Europeans suffer from an actual cow’s milk allergy.
A cow’s milk allergy usually appears in infancy after the first few times milk is consumed. The symptoms can occur immediately or after a period of up to two days. But they can always be linked to milk consumption. If milk is occasionally tolerated, it is unlikely that the symptoms are caused by an allergy.
Cow’s milk contains many proteins that can trigger allergies. Those most commonly involved in allergic reactions are casein and the whey proteins beta-lactoglobulin and alpha-lactalbumin. Most allergic individuals react to several proteins at once.
Casein is heat stable and is not destroyed through cooking. On the other hand, the proteins beta-lactoglobulin and alpha-lactalbumin are heat sensitive. Therefore patients who only react to these heat-sensitive proteins may be able to tolerate products containing milk that has been cooked or baked.
Many people with a cow’s milk allergy are also allergic to sheep’s or goat’s milk. This is because the proteins in the milk of other animals are similar to those found in cow’s milk and can also be considered dangerous by the immune system.
In rare cases, human milk can also trigger an allergic reaction. This happens when breastfeeding infants react to proteins (usually cow’s milk proteins) consumed by the mother. The children pass bloody/slimy stools but otherwise appear healthy. The symptoms disappear when the allergen is identified and eliminated from the mother’s diet.
Symptoms occur within minutes, but may also appear up to 48 hours after milk consumption. The skin is most commonly affected, along with the gastrointestinal tract in many cases. Skin symptoms include redness, hives and itching. Facial swelling also occurs in some patients. In delayed reactions, atopic dermatitis can be triggered or worsened. Gastrointestinal symptoms include diarrhoea or constipation, nausea and vomiting. Infants may experience delayed growth.
As with other food allergies, the airways can be affected, resulting in allergic rhinitis or asthma symptoms. In rare cases, anaphylactic shock with difficulty breathing and circulatory collapse may occur.
Although cow’s milk allergies are among the most common food allergies in childhood, the prognosis is good. In many patients, the allergy subsides by the age of three. Around 80 per cent of children are symptom-free by the time they reach school age.
The allergist can perform a test 6 to 18 months following diagnosis to check whether the allergy is still present so that children may resume milk consumption as soon as possible.
As a first step in diagnosing a milk allergy, the doctor asks the patient about his or her eating habits and symptoms. If an allergy is suspected, skin and/or blood tests are conducted (depending on the patient’s age and symptoms) in order to confirm it. These tests reveal an allergic disposition to certain substances but do not provide evidence of an actual allergy. For this reason, an additional diagnostic procedure, the provocation test, is conducted to rule out any doubts. For this test, the patient eliminates the allergen from the diet for a certain period. He or she is then given small amounts of milk proteins under medical supervision. The results confirm whether milk triggers an allergic reaction.
The distinction must be made between a milk allergy and lactose intolerance, a non-allergic disease caused by insufficiency of the enzyme lactase, which breaks down lactose, the sugar in milk. Symptoms of lactose intolerance include bloating and diarrhoea, and can be improved by eliminating lactose from the diet. However, lactose-free products are not helpful for people with a milk allergy, since they still contain the milk proteins that trigger the allergy.
A difficult diagnosis
The diagnosis is not easy. One reason is because there are different ways that the immune system mounts a defence against certain proteins in cow’s milk. In two out of three cases, the body has a reaction referred to as type I hypersensitivity, [Bitte „type I hypersensitivity“ mit folgendem internen, in einem neuen Fenster öffnenden Link unterlegen: https://www.ecarf.org/en/information-portal/general-allergy-info/what-happens-in-my-body-when-i-have-an-allergy/] in which a certain antibody, immunoglobulin E, plays an important role. The resulting symptoms usually occur as soon as one to two hours after drinking milk. IgE-mediated allergies can be detected through blood or skin tests.
A more complex physical defence occurs in the remaining third of the cases. The immune response is triggered through type II-IV hypersensitivity, [Bitte „type II-IV hypersensitivity“ mit folgendem internen, in einem neuen Fenster öffnenden Link unterlegen: https://www.ecarf.org/en/information-portal/general-allergy-info/what-happens-in-my-body-when-i-have-an-allergy/] which does not involve all of the reaction pathways. Symptoms are mainly gastrointestinal (e.g. vomiting, bloating, diarrhoea, cramps). Allergic skin rashes are not as common. This often makes it difficult to diagnose the allergy. The only thing that usually helps is to exclude dairy products for two to six weeks. If the child has no symptoms while abstaining from milk (elimination trial), milk is then reintroduced in increasing doses – for example, starting with a drop on the lower lip under medical supervision (Sackesen et al. 2019).
Not everything is off limits
If a cow’s milk allergy is detected, the essential nutrients from milk, such as calcium, proteins, vitamins and iodine, can be obtained from other foods. In addition, most of the children are still able to consume certain dairy products.
High temperatures can change the proteins in cow’s milk in such a way that immunoglobulin E no longer reacts to them. Three out of four children with IgE-mediated allergy can tolerate dairy products that have been heated for 30 minutes or longer at a minimum of 180 degrees Celsius. Stephanie Leonard from the Rady Children’s Hospital in San Diego, California, analysed the most important studies on this topic. She came to the conclusion that the ideal solution for infants with cow’s milk allergy would be to consume baked dairy products. This is not only because they would avoid an allergic reaction, but also because the allergic reactions decrease over time: “Regular ingestion appears to accelerate the development of tolerance to regular milk products,” said the allergy specialist (Leonard 2016).
The British Society for Allergy and Clinical Immunology (BSACI) provides specific guidelines on how to proceed with desensitisation using these products (Luyt et al. 2014). With the four-stage ‘milk ladder’, children with cow’s milk allergy are exposed step by step to increasing amounts of dairy protein:
- Stage 1: Biscuits containing less than 1 gram of milk protein.
- Stage 2: Baked or heated cow’s milk products, for example, cakes, waffles or pancakes, and butter or margarine.
- Stage 3: Products containing cooked cheese or heated milk, for example, cheese sauce, rice pudding, pizza.
- Stage 4: Uncooked cheese, non-yoghurt desserts, for example, ice cream or chocolate mousse, UHT milk.
The BSACI recommend this approach for children with an IgE-mediated allergy to cow’s milk proteins who have had no symptoms within the last six months. The quantity should be gradually increased each time a new product is introduced. For example, the ‘biscuit dose’ should be increased from a single crumb to a whole biscuit over a period of five weeks.
The best way to reduce the symptoms of a milk allergy is to avoid milk and other dairy products such as butter, cheese, yogurt and curd cheese. Milk ingredients are often used as additives in industrially processed foods such as sausages or ready meals. These additives must be clearly labelled as required by European food regulations.
Allergic infants and children cannot eliminate cow’s milk without a replacement, since milk is the most important source of calcium at this age and provides high-quality protein and B-vitamins. If a milk allergy is diagnosed, nutritional counselling is recommended. Infants are given extensively hydrolysed formulas, a special form of nutrition in which the milk protein is broken down to such an extent that it is no longer allergenic. As an alternative, amino acid formulas can be used. These do not contain any cow’s milk and provide only individual amino acids as the protein source. After the first year, soya milk can also be given if the child does not have a soya allergy. Children less than one year of age should not be given soya, since there is no clear evidence as to whether soya affects the human hormonal system. Oat milk, almond milk and rice milk are not suitable replacements for cow’s milk; children should only consume them once they are old enough to obtain essential nutrients from meat, grains, fruits and vegetables.
If the cow’s milk allergy is so severe as to trigger anaphylactic shock from exposure to even small amounts of milk protein, emergency medications must be kept on hand at all times in the form of an emergency kit containing an adrenaline auto-injector, a corticosteroid (in liquid or tablet form) and an antihistamine (in liquid or tablet form).
Prof. Dr. med. Dr. h.c. T. Zuberbier
Last changes made: July 2016
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